ASBI-Construction-Practices-Handbook-for-Concrete-Segmental-and-Cable-Supported-Brdiges.pdf

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES Published June 2008

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AMERICAN SEGMENTAL BRIDGE INSTITUTE 9201 N. 25"' Avenue, Suite 150B. Phoenix. Arizona 85021-2721 Tel: (602) 997-9964 Fax: (602) 997-9965 e-mail: [email protected] web: www.asbi-assoc.org

©Copyright 2008 by the American Segmental Bridge Institute. All Rights Reserved. Printed in the United States of America. This book, or parts thereof may not be reproduced in any form without permission of the publisher.

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Billinger Berger lngeniEurbau GmbH Bibliothek

MASTER TABLE OF CONTENTS

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CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTERS 1.0-17.0 FHWA Post-Tensioning Tendon Installation and Grouting Manual

CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION

)

1.0

Introduction and Overview of Segmental Construction

3

1.1

Purpose

3

1.2

Advantages of Segmental Construction

3

1.3

Structure Types

3

1.3.1

Precast Segmental Span-by-Span

3

1.3.2

Precast Segmental Balanced Cantilever Bridges

5

1.3.3

Precast Segmental Progressive Placement

6

1.3.4

Precast Segmental Arches

7

1.3.5

Cast-In-Place Segmental Balanced Cantilever Bridges

8

1.3.6

Cast-In-Place Segmental Arches

1.3.7

Cast-In-Place Segmental Incremental Launching

10

1.3.8

Precast and Cast-in-Place Segmental Cable-Stayed Bridges

11

1.3.9

Heavy Segmental

13

1.3.9.1

Confederation Bridge, New Brunswick- Prince Edward Island, Canada

1.3.9.2 San Francisco- Oakland East Bay Skyway Bridge 1.4

Documentation of Design Assumptions in Contract Documents

9

13 15 17

CHAPTER 2.0 TERMINOLOGY

2.0 Terminology

3

2.1 General Terminology

3

2.2 Post-Tensioning and Grouting Terminology

8

CHAPTER 3.0 CONSTRUCTION OF PRECAST SPAN-BY-SPAN BRIDGES

3.0

Construction of Precast Segmental Span-by-Span Bridges

3

3.1

3

3.2

Introduction Advantages of Segmental Span-by-Span Bridges

6

3.3

Typical Span-by-Span Erection Sequence

8

3.4

Special Considerations

3.5

Safety

18

3.6

Summary

20

17

) Table of Contents, Chapters 1.0- 17.0 and Post-Tensioning Tendon Installation & Grouting Manual

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CHAPTER 4.0 CONSTRUCTION OF PRECAST BALANCED CANTILEVER BRIDGES 4.0

Construction of Precast Segmental Balanced Cantilever Bridges

4.1

Overview

3

4.1.1

Basics of the Technique

3

4.1.2

Typical Segments Configurations

4

4.1.3

Segment Details

5

4.1.3.1

Cantilever Tendon Anchorages

6

4.1.3.2 Continuity Anchors

7

4.1.3.3 Temporary Post-Tensioning

7

4.1.3.4 Permanent Ducts

7

4.1.3.5 Web Keys

9

4.1.3.6 Flange Keys Casting Yard and Transportation 4.2

9

4.2.1

9

Forms

'

3

9

4.2.2

Detailing and Workmanship

10

4.2.3

Geometry Control

13

4.3.4

13

4.3

Lifting Details Typical Erection Cycle

4.3.1

Overview

14

14

4.3.2

Epoxy

15

4.3.3

Temporary PT

16

4.3.4

Tendon Installation and Jacking

17

4.3.5

Grouting

18

4.4

Erection Equipment and Methods

19

4.4.1

20

4.4.2

Crane Beam and Winch

4.4.3

Erection Gantry

22

4.4.4

Hauler

27

4.5

Special Topics Surveying and Deflections

27

4.5.1 4.5.2

Pier Segments

28

4.5.2.1

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21

27

Cast-in-Place

28

4.5.2.2 Precast Pier Segment

30

4.5.2.3 Precast Shell Expansion Joints 4.5.3

31 33

4.5.4

Mid-Span Closure

37

4.5.6

Temporary Access Openings

38

4.6

Engineering

38

4.6.1

Built-in Loads

38

4.6.2

Erection Loads

39

4.6.3

Cambers and Deflections

39

4.6.4

Temporary Post-Tensioning

39

Table of Contents, Chapters 1.0- 17.0 and Post-Tensioning Tendon Installation & Grouting Manual

2 of9

CHAPTER 5.0 CONSTRUCTION OF CAST-IN-PLACE BALANCED CANTILEVER BRIDGES

5.0 5.1 5.2

Construction of Cast-in-Place Balanced Cantilever Bridges Introduction Construction Methods

3 3 6

CHAPTER 6.0 INCREMENTAL LAUNCHING SEGMENTAL BRIDGES

6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7

Construction of Incremental Launching Segmental Bridges

3

Introduction

3

Advantages of Incremental Launching Segmental Bridges Characteristics of Incremental Launching Segmental Bridges Typical Construction Sequence Launching System and Equipment Summary Reference

4 6 12 13 18 18

CHAPTER 7 Special Requirements for Construction of Concrete Segmental Cable-Stayed Bridges

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7.0 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.5. 7.5.1 7.5.2 7.5.3 7.5.4 7.6 7.7 7.8 7.8.1 7.8.2 7.9

Cable-Stayed Bridges Introduction Cable-Stayed Structure Critical Construction Phases Deck, Stay Cable Stresses Unbalanced Loads Other Critical Construction Loads Geometry Control Casting Curves Geometry Control for Prescast Box Girder Segments Geometry Control for Cast-in-Place Box Girders Geometry Control for Cast-in-Place Flexible Decks Stay-Cable System Quality Control Stay-Cable Types Bearing Plate, Recess Pipe Installation Stay-Cable Pipe Installation Installation of Other Stay-Cable Components Control of Stay-Cable Forces Fatigue Testing Extradosed Bridges Design Concept Construction of Extradosed Bridges

Conclusion References

Notable Concrete Cable-Stayed Bridges in the United States

3 3 3 5 5 11 13 14 14 15 20 20 20 20 20 22 23 24 26 26 26 28 29 29 29


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CHAPTER 8.0 SEGMENTAL SUBSTRUCTURES

8.0 8.1 8.2 8.3 8.4 8.5

Segmental Substructures Introduction Project Examples Precasting Operations

Erection Operations Summary

3 3

3 7 10 11

CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS

9.0 9.1 9.1.1 9.1.2 9.1.2.1 9.1.2.2 9.1.2.3 9.1.2.4 9.1.3 9.1.3.1 9.1.3.2 9.1.3.3 9.1.3.4 9.1.3.5 9.1.4 9.1.4.1 9.1.4.2 9.1.5 9.1.5.1 9.1.5.2 9.1.5.3 9.1.5.4 9.1.6 9.1.9.1 9.1.9.2 9.1.9.3 9.1.9.4 9.1.9.5 9.1.7 9.1.7.1 9.1.7.2 9.1.7.3 9.1.7.4 9.1.7.5 9.1.7.6 9.1.7.7 9.1.7.8

Segment Production

Casting Yard Planning and Setup Introduction Location Acreage Utilities Existing Buildings Water Access Existing Site Conditions Soil Conditions

Drainage/Storm Water Plan Wetlands Issues

Security Slip or Dock Conditions Receiving/Delivery Delivery of Segments Material Deliveries Site Preparation Local Permits-Developer Fees Grubbing and/or Clearing Grading-Drainage, Runoff Foundations

Procurement Forms Batch Plant Steam Generator

Cranes (Gantry Cranes, Tower Cranes and Segment Haulers) Auxiliary Equipment

Facilities Office Trailer Locations Form Locations

Rebar Jig Locations Warehouse, Material Storage Location

Steam Generator Location, Piping Requirements Portable Toilet Locations Temporary Fuel Storage Trash, Scrap, Recyclables

3 3 3 6 6 6 6 7 7 7 8 8 8 8 8 8 9 10 10 10 10 10 12 12 15 15 16 17 20 20 21 23 24 24 24 24 25

Table of Contents, Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual

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CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS Continued

9.1.8 9.1.9 9.2 9.2.1 9.2.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.14.1 9.14.2 9.14.3 9.14.4 9.14.5

Post Casting Summary- Casting Yard Planning and Setup Long Line and Short Line Forms Long Line Casting Bed Short Line Casting Bed Match Casting Casting Curve Fabrication of Rebar Cage with Post-Tensioning Ducts and Hardware Installation of Post-Tensioning Ducts Handling the Prefabricated Rebar Cage Rebar Cage in Casting Cell Setting the Match Cast Segment Placing Concrete Finishing the Top Surface Curing

Forms

~ ~')\A. "'-~

J fri ~.s

Special Situations- Elevated Light Rail Construction Rail Construction LRT Electrification

Crossover Construction Grounding Requirements LRT Conclusion

25 26 27 27 33 37 38 39 41 41 42 42 43 45 46 47 50 50 52 52 53 55

CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS

10.0 10.1 10.1.1 10.1.2 10.1.3 10.2 10.2.1 10.2.2

Procedures for Handling, Transporting and Erecting Precast Segments

3 Methods of Lifting Precast Segments 3 Lifting Holes Cast in the Top Slab of Segments 3 Inserts Embedded in the Segment Webs and Protruding Above the Top Slab 4 Lifting Slings or C Hook Frame 5 Handling and Transporting of Precast Segments in Precast Yard 6 Handling precast segment from the new-cast position to the match-cast position 6 Handling and Transporting of Precast Segments from the Casting Area to the Storage Area

10.3 10.3.1 10.3.1.1 10.3.1.2 10.3.1.3 10.3.2 10.3.2.1 10.3.2.2 10.3.2.3 10.3.3 10.4 10.4.1

Transporting Precast Segments from the Precast Yard to the Erection Site Transporting Precast Segments via Water Using Barges Loading Transport

Unloading Transporting Precast Segments Off-site via Land Loading Transport Unloading Transporting Precast Segments On-site via Land Erection of Precast Segmental Bridges Factors for the Selection of Precast Segmental Bridge Erection Methods

6 11 11 11 12 12 14 14 14 15 15 19 19


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CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS Continued

10.4.2 10.4.2.1 10.4.2.1.1 10.4.2.1.2 10.4.2.1.3 10.4.2.1.4 10.4.2.1.5 10.4.2.1.6 10.4.2.2 10.4.2.2.1 10.4.2.2.2 10.4.2.2.3 10.4.2.2.4 10.4.2.3

Erection Methods for Precast Segmental Bridges Erection Methods for Span-by-Span Type Bridges Underslung Trusses with Crane on Ground or Barge Mounted on Water Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck Erection with an Overhead Gantry Full Span Erection wtlh Winches I Strand Jacks Full Span Carrier I Erector Full Span Erection on Shoring Falsework Erection Methods for Balanced Cantilever Bridges Balanced Cantilever Erection by Crane on Ground or on Water Balanced Cantilever Erection by Overhead Gantries Balanced Cantilever Erection with Beam and Winch/Strand Jacks Balanced Cantilever Erection with Special Erectors Erection Methods Conclusion

21 22 22 24 25 27

28 29 30 30 32 34 36 37

CHAPTER 11.0 ERECTION DETAILS

11.0 11.1 11.1.1 11.1.1 11.1.2 11.1.2 11.1.3 11.1.3 11.1.4 11.1.4 11.1.5 11.1.5 11.1.6 11.1.6 11.1.7 11.1.7 11.1.8 11.1.8 11.2 11.3 11.4 11.5 11.6 11.7

Erection Details Permanent Post-Tensioning Anderson Technology Corporation- Transparent Sheathing Anderson Technology Corporation- Super Corrosion Protective (Supra Strand) AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Multi Plane AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Flat Anchorage DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental Construction DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental and CIP Construction Freyssinet Post-Tensioning Systems- Freyssinet Post-Tensioning Hardware for Segmental Bridges/G-Range Post-Tensioning Systems Freyssinet Post-Tensioning Systems- Freyssinet F-Range Post-

3 3 4

Tensioning Systems

11 12 13 14

Mexpressa -Jacks and Pumping Units Mexpressa -Anchorages and Couplers SDI Post-Tensioning Systems and Services SDI Type C Multistrand Anchorage/Type C4.6 Multistrand Anchorage/ Type D Multistrand Anchorage VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type ECI/Type ES/Type E/PT-Pius Duct System VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type SAIVSLAB+® System Williams Form Engineering Corporation- The Williams System Williams Form Engineering Corporation-150 KSI All-Thread Bar Temporary Post-Tensioning Post-Tensioning Safety Issues Lifting Segments for Erection Temporary Supports Midspan Closure Construction Schedule and Sequence


5 6 7

8 9 10

15 16 17 18 19 20 23 30 31 32 33

6 of9

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CHAPTER 12.0 EPOXY JOINTING, DUCT COUPLER DEVICES, AND PREPACKAGED GROUT 12.0 Epoxy Jointing, Duct Coupler Devices, and Prepackaged Grout

Purposes of Epoxy Types and Application of Epoxy

12.3 12.3.1

FREYSSINET Post-Tensioning Systems

6 7

12.3.2 12.3.3 12.4 12.4.1

VSL Segmental Duct Coupler

8

12.4.1

BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction

12.4.2 12.4.3

SIKA Corporation Epoxy Resin for Segmental Bridge Construction

14 15

SIKA Corporation Prepackaged Grouts for Segmental Bridge Construction

16

Duct and Duct Coupler Devices

General Technologies, Inc. Precast Segmental Duct and Duct Coupler Prepackaged Grout

CHAPTER 13.0 GEOMETRY CONTROL 13.0 Geometry Control

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.9.1 13.9.2

General Casting Cell Geometry Control System Tools Used for Geometry Control Geometry Control of the First Pier Segment Field Survey Checking During Erection Systematic Error Achieved Profiles Pier Shaft Segments Temperature Effects Temperature Expansion and Contraction Temperature Gradient

CHAPTER 14.0 BEARINGS AND EXPANSION JOINTS 14.0 Bearings and Expansion Joints

14.1

Bearings

14.1.1 14.1.2 14.1.3

Bearing Installation

14.1.4 14.1.5

Temperature Adjustment

14.2 14.2.1 14.2.2 14.2.3 14.2.4 14.2.5 14.2.5 14.2.6 14.2.6 14.2.7 14.2.7

Mortar Pads Horizontal-Position of Bearings Direction of Movement Expansion Joints

,-'

9 10 13

3 3 7 12 13 13 14 15 15 15 15 18

3 3 3 6 6 6 6

Expansion Joints Supplied by Freyssinet LLC

7 7 8 9 10 12 13 14 15

Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation

16

Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation

17

Strip Seal Systems Molded, Steel Reinforced Rubber Cushion Bolt-Down Systems (Transfiex or Wabofiex) Modular Joint Systems Finger Joints Bearings and Expansion Joints Supplied by The D.S. Brown Company Bearings and Expansion Joints Supplied by The D.S. Brown Company Expansion Joints Supplied by Freyssinet LLC

Table of Contents,' Chapters 1.0 - 17.0 and Post-Tensioning Tendon Installation & Grouting Manual (

3 3

BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction

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3

12.1 12.2

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CHAPTER 15.0 LESSONS LEARNED

15.0

Lessons Learned

3

15.1.0

General

3

15.2.0

Design Lesson Learned

4

15.2.1

Reinforcing Details

4

15.2.2

Tendon and Duct Detailing

4

15.2.3

Cracking

6

15.2.4

Designing for Construction Tolerance

7

15.2.5

Principal Stresses and Web Shear

7

15.2.6

Flange Shear Stresses

7

15.2.7

Asymmetric Sections and Rotated Principal Axes

9

15.2.8

Shear Distribution of Multiple Webs

9

15.2.9

Shear Lag

9

15.2.10 Combination of Transverse Bending and Shear

10

15.2.11 Built-in Loads

10

15.2.12 Tendon Losses

10

15.2.13 Bottom Slab Drainage Details

10

15.2.14 Inspection Access

11

15.3.0

Construction Lesson Learned

12

15.3.1

12

15.3.2

General Equipment Requirements

15.3.3

Construction Loads

12

15.3.4

Truss Stability

13

15.3.5

Bearing of Truss Supports Warping Under Concentrated Loads

14

15.3.6 15.3.7

Out-of-Balance Moments

14

15.3.8

Alignment and Geometry Problems

14

15.3.9

Geometry Control in Gore Regions

15

12

14

15.3.10

Fit of Match Cast Segments

15

15.3.11

Steam Curing and Warping

15

15.3.12

Short Tendon Elongations

16

15.3.13

Tendon Blockages

16

15.3.14

Tendon Pop-out

16

15.3.15 Epoxy Not Setting

18

15.3.16 Freezing of Water in Ducts and Recess Pockets

18

15.4.0

19

References

CHAPTER 16.0 CONSTRUCTION ENGINEERING & INSPECTION (CEI) OF SEGMENTAL CONSTRUCTION

16.0

Project Site Roles

2

16.1

Motivation of Stakeholders

3

16.2

CEI Early Involvement

4

16.3

Remote Precast Yard

4

16.4

16.7

Preconstruction Conference Engineering Submittals, Shop Drawings, RFis Technical Workshops I Submittals I Format Critical Issues early on at Precast Yard

16.8

Concrete Mix Designs

16.5 16.6

4 4 5 5

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CHAPTER 16.0 CONSTRUCTION ENGINEERING & INSPECTION (CEI) OF SEGMENTAL CONSTRUCTION Continued

16.9 16.10 16.11 16.12 16.13 16.14 16.15 16.16 16.17 16.18 16.19 16.20

Casting Yard Quality Control/ Geometry Control

Review of Erection Procedures Confirmation of Erection Procedures Post Tensioning and Grouting

Bearings, Expansion Joints and Seismic Devices Highway vs. Rail Bridges Record Keeping I As-Builts Safety

Environmental Issues Claims and Changes Successful Project Ingredients Summary

5 6 6 6 7 7 7 7 8 8 8 9

CHAPTER 17.0 CONSTRUCTION INSPECTION GUIDELINES FOR SEGMENTAL CONCRETE BRIDGES

)

17.1 17.1.1 17.1.2 17.2 17.3 17.4 17.5 17.6 17.7 17.8 17.9 17.9.1 17.9.2 17.9.3 17.10 17.11 17.12 17.13 17.14 17.15 17.16 17.17 17.18 17.19 17.20 17.21 17.22 17.23

Recommended Practice for Initial Inspection of Forms

Form Dimensions and Tolerances Form Operation Recommended Practice for Daily Inspection of Forms Recommended Practice for Inspection of Cut and Bent Rebar Recommended Practice for Inspection of Rebar Cages

3 3 5 7 8 11

Recommended Practice for the Initial Inspection and Storage of Post-Tensioning Hardware 15 Recommended Practice for Inspection of Post-Tensioning Hardware In the Reinforcement Cage 17 Recommended Practice for Resolution of Rebar Conflicts

18 Recommended Practice for Inspecting Post-Tensioning Hardware in the Form 20 Recommended Practice for Inspection of the Setting of Matchcast Segments 21 On-Site Hardware 21 Measuring Instruments 22 Observations in the Casting Cell 23 Recommended Practice for Concreting Segments 26 Recommended Practice for Inspection of Curing of Segments 28 Recommended Practice for Inspection of Stripping Forms and Bond Breaking 29 Recommended Practice for Inspection of Segment Handling in the Casting Yard 30 Recommended Practice for Inspection of Repairs Made to Segments 31 Recommended Practice for Inspection of Segment Storage 33 Recommended Practice for Inspection of Segments for Payment 34 Recommended Practice for Inspection of Segment Transportation 35 Recommended Practice for Inspection of Erection Equipment 36 Recommended Practice for Inspection of Falsework 37 Recommended Practice for the Inspection of Epoxy Joints 38 Recommended Practice for Tendon Stressing 40 Recommended Practice for Inspection of Grouting 40 Recommended Practice for Inspection of Cast-in-Place Segmental Structures 40

FHWA Post-Tensioning Tendon Installation and Grouting Manual


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Construction Practices Handbook For Concrete Segmental and Cable-Supported Bridges ACKNOWLEDGEMENTS In addition to the acknowledgements of individuals who were primary authors of chapters of the First Edition, the following individuals were primarily responsible for writing or revising chapters of the second edition: Chapters 2 & 11

Post-Tensioning Terminology and Post-Tensioning Safety Shahid Islam, Dywidag-Systems International USA, Inc.

Chapter 3

Construction ofPrecast Segmental Span-by-Span Bridges Jim Schneiderman, PCL Civil Constructors, Inc.

Chapter 4

Construction ofPrecast Segmental Balanced Cantilever Bridges Ben Soule, International Bridge Technologies, Inc. David Goodyear, T. Y. Lin International, Inc. Scott McNary, McNary, Bergeron Associates, Inc.

Chapter 5

Construction of Cast-in-Place Balanced Cantilever Bridges Sean Bush, PCL Civil Constructors, Inc.

Chapter 6

Construction of Cast-in-Place Incrementally Launched Bridges Marco Rosignoli, HNTB Corporation Takahiro Kakuta, PSM Construction, USA, Inc.

Chapter 7

Special Requirements for Construction of Concrete Segmental Cable-Supported Bridges Daniel Tassin, International Bridge Technologies, Inc.

Chapter 9

Production ofPrecast Segments Arthur Palmer, Consultant

Chapter IO

Procedures for Handling Transporting and Erecting Precast Segments Elie Homsi, Flatiron Constructors, Inc. Riccardo Castracani, DEAL/Rizzani De Becher USA

Chapter 13

Geometry Control Alan Moreton, Corven Engineering, Inc.

)

Lessons Learned

Chapter I5

Chapter I6

)

Cliff Freyermuth, ASBI Ben Soule, International Bridge Technologies, Inc. Ralph Salamie, Kiewit Pacific Company Construction Engineering Inspection ofSegmental Construction Ian Hubbard, Parsons Brinckerhoff, Inc. Thomas DeHaven, FIGG John W. Jordan, Earth Tech, Inc.

Acknowledgements (First Edition)

"A Guide to the Construction of Segmental Bridges" developed by and for the Florida Department of Transportation; October 1989, was used by the American Segmental Bridge Institute Construction Practices Committee as a source document in the development of the "Guidelines for Construction of Segmental Concrete Bridges" presented in this publication.

Contributions to the Handbook by individuals who were primary authors of chapters of this section of the manual are acknowledged as follows:

Chapter 3

Construction of Precast Segmental Span-by-Span Bridges - R. Kent Montgomery, FIGG

Chapter4

Construction of Precast Segmental Balanced Cantilever Bridges -David Jeakle, URS Corporation

Chapter 5

Construction of Cast-in-Place Balanced Cantilever Bridges -Teddy Theryo, Parsons Brinckerhoff, Inc.

Chapter 13

Segmental Substructures - R. Kent Montgomery, FIGG

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ASBI Construction Practices Committee May2008

)

JOHN D. ARMENI, Chair Anneni Consulting Services, LLC Crossings at Three Bridges 4411 Suwanee Dam Road, Suite 750 Suwanee, GA 30024 Phone: (770) 904-4178 Fax: (770) 904-3671 Cell (404) 414-3743

DAVID GOODYEAR Vice President T. Y. Lin International 1115 W. Bay Drive NW, Suite 206 Olympia WA 98502 (360) 754-0544 Fax: (360)754-1714 e-mail: [email protected]

e-mail: [email protected] SEAN BUSH PCL Civil Constructors, Inc. 2804 E. Jackson Street Orlando, FL 32803 Cell: (407) 896-5960 (407) 896-5963 e-mail: [email protected]

ELIE H. HOMSI Vice President Engineering Services Flatiron Constructors, Inc. 100901-25 Frontage Road Longmont CO 80504 (720) 49+8134 Fax (720) 494-8150 e-mail: [email protected]

DAN CABELLO

IAN HUBBARD

Bayshore Concrete Products Corporation

Parsons Brinckerhoff Construction Services

POB230 Cape Charles, VA 23310 (757) 331-2300 (757) 331-2501 e'mail : [email protected]

15430 35th Ave, South Tukwila, WA98!88 (206) 3705555 (206) 444-6371 E-mail: [email protected]

RICCARDO CASTRACANI DEAL/Rizzani de Eccher, USA 2999 NE 191st Street, Suite 901 Aventura, FL 33180 (305) 932-9700 Fax: (305) 932-9550

SHAHIDUL ISLAM, PH.D. Dywidag-Systems International USA. Inc. PT Engineering Unit 320 Marmon Drive Bolingbrook, IL 60440 ( 630) 972-4028 Fax: (630) 739-1405 E-mail: Shahid.islam@dsiamericacom

e-mail: rcastracani@rdeusanet TOM DeHAVEN FIGG 1585 Thomas Center Drive, Suite 106 Eagan, MN 55122 (651) 251-3444 Fax: (651) 251-3445 e-mail: [email protected] GOWEN DISHMAN HNTB c/o 3408 S. Lakeshore Drive Lake Village, AR 71653 662-347-6506 [email protected] ANDREW A. GHOFRANI, P.E. Design/Build Manager Granite Construction, Inc. 585 W. Beach Street, Building #I Watsonville, CA 95076 (831)728-7548 Fax: (831) 728-7513 e-mail: [email protected]

) "

TAKAHIRO KAKUTA PSM CONSTRUCTION USA, INC. 111 Anza Blvd., Suite 415 Burlingame, CA 94010 (650) 344-9109 Fax: (650) 344-9199 e-mail : [email protected] KEEFER, MARK VSL 282 Alpine Drive Front Royal, VA 22630 Fax: (703) 451-0862 Mobile: (571) 437-3399 e~mail: [email protected] RICKLAIL Southern Fonns. Inc. 445 Hales Bar Road Guild, TN 3 7340 (423) 942-7000 Fax: (423) 942-1902 e-mail: [email protected]

ASBI Construction Practices Committee May2008 MYINTLWIN

FHWA Office ofBridge Technology lllBT, Room 3203, 400 7"' Street, SW Washington, DC 20590 (202) 366-4589 Fax: (202) 366-3077

ARTIIUR PALMER 603 Hudson River Road POBox248 Waterford, NY 12188 (H) 518-235-3647 (C) 518-810-6886 e-mail: [email protected]

e-mail: [email protected] RALPH SALAMIE SCOTT MCNARY McNary Bergeron & Associates 565 Burbank Street Suite A Broomfield, CO 80020 (CO .office only) (860) 388-2267 Fax: 860-388-2268

e-mail: [email protected] SAM! MEGALLY PBS&J 9275 Sky Park Court, Suite 200 San Diego, CA 92123 (858) 514-1035 Fax: (858) 514-1001 e-mail: [email protected]

MARK MILICI Dywidag Systems International, USA, Inc. 525 Wanaque Avenue, Suite LLI Pompton Lakes, NJ 07442-1833 (973) 276-9222 Fax: (973) 276-9292 e-mail: [email protected] ALAN J. MORETON

Corven Engineering, Inc. 2882 Remington Green Circle Tallahassee, FL 32308 (850) 386-6800 Fax: (850) 386-9374

e-mail: [email protected] STEVE PABST

Watson Bowman Acme-Corporation - A BASF Company 95 Pineview Drive Amherst, NY 14228 (716) 691-7566 Fax: (716) 691-9239 e-mail: steve.pabst@basfcom

Kiewit Pacific 2200 Columbia House Blvd. Vancouver, W A 98661 (360) 693-1478 Fax: (360) 693-5582 e-mail: [email protected] JIM SCHNEIDERMAN PCL Civil Constructors, Inc. 3810 Northdale Blvd., Suite 200 Tampa, FL 33624 (813) 264-9500 Cell: (813) 781-0047 e-mail: [email protected] BEN SOULE

Intemationa1 Bridge Technologies, Inc. 9325 Sky Park Court, Suite 320 San Diego, CA 92123 (858) 566-5008 Fax:.(.858) 566-1220

e-mail: [email protected] EDWARD TRIPODI ETIPTC 3430 Tumingwind Lane Winter Garden, Fl. 34787 (612) 328-7778 e-mail: [email protected] JOHN WHITE

Williams Form. Engineering Corp. 8165 Graphic Drive, N.E. Belmont, MI 49306-9448 (616) 866-0815 Fax: (616) 866-1810

e-mail: [email protected] CLIFFORD L. FREYERMUTH, Facilitator ASBI 9201 N. 25th Avenue, Suite 150B Phoenix, AZ 85021 (602) 997-9964 Fax: (602) 997-9965 e-mail: [email protected]

) 2

DISCLAIMER This publication is intended for the use of professionals competent in evaluating the significance and limitation of its contents and who will accept responsibility for the application of the materials it contains. American Segmental Bridge Institute makes no warranty regarding the recommendations contained herein, including warranties of quality, workmanship or safety, express or implied, further including, but not limited to,. implied warranties or merchantability and fitness for a particular purpose.

THE

AMERICAN SEGMENTAL BRIDGE INSTITUTE SHALL NOT BE LIABLE FOR ANY

DAMAGES,

INCLUDING

CONSEQUENTIAL

DAMAGES,

BEYOND

REFUND OF THE PURCHASE PRICE OF THIS PUBLICATION. The incorporation by reference or quotation of material in this publication in any specifications, contract documents, purchase orders, drawings or job details shall be done at the risk of those making such reference or quotation and shall not subject the American Segmental Bridge )

Institute to any liability, direct or indirect, and those making such reference or quotation shall waive any claims against the American Segmental Bridge Institute.

American Segmental Bridge Institute 9201 N. 25th Avenue, Suite 150-B Phoenix. AZ 85021 Tel: 602-997-9964 Fax: 602-997-9965 Email: [email protected] Website: www.asbi-assoc.org

)

)

TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION

1.0

Introduction and Overview of Segmental Construction

3

1.1

Purpose

3

1.2

Advantages of Segmental Construction

3

1.3

Structure Types

3

1.3.1

Precast Segmental Span-by-Span

3

1.3.2

Precast Segmental Balanced Cantilever Bridges

5

1.3.3

Precast Segmental Progressive Placement

6

1.3.4


7

1.3.5

Cast-In-Place Segmental Balanced Cantilever Bridges

8

1.3.6

Cast-In-Place Segmental Arches

9

1.3.7

Cast-In-Place Segmental Incremental Launching

10

1.3.8

Precast and Cast-in-Place Segmental Cable-Stayed Bridges

11

1.3.9

Heavy Segmental

13

1.3.9.1 Confederation Bridge, New Brunswick- Prince Edward Island, Canada

13

1.3.9.2 San Francisco- Oakland East Bay Skyway Bridge

15

1.4

17

Documentation of Design Assumptions in Contract Documents

Chapter 1.0 Introduction and Overview of Segmental Construction

1 of 17

TABLE OF FIGURES CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 1.0 INTRODUCTION AND OVERVIEW OF SEGMENTAL CONSTRUCTION

Figure 1.1

Erection Truss in Place to Receive Segments

4

Figure 1.2

Erecting Segments on the Glenwood Canyon Project

4

Figure 1.3

Common Segment Installation Methods

5

Figure 1.4

Erection of Cantilever N-E5 with Segment Erector. Cantilever W-N 10 in the Foreground

5

Figure 1.5

Erection Scheme for Progressive Placement

6

Figure 1.6

Construction of the Linn Cove Viaduct, NC

6

Figure 1.7

Construction of Natchez Trace Arch Bridge

7

Figure 1.8

Placement of Keystone of Natchez Trace Arch Bridge

7

Figure 1.9

Construction of Cast-in-Place Balanced Cantilever Bridges

8

Figure 1.10

Construction of the Crooked River Bridge Arch, OR

9

Figure 1.11

Hoover Dam Bypass Arch Bridge Rendering

9

Figure 1.12

Incremental Launching

10

Figure1.13

Launching Nose on Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)

10

Launching Equipment for the Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)

11

Figure 1.15

C & D Canal Bridge, DE

12

Figure 1.16

Sunshine Skyway Bridge, Tampa, FL

12

Figure 1.17

Dames Point Bridge, Jacksonville, FL

13

Figure 1.18

Confederation Bridge Casting Yard

13

Figure 1.19

Erection of 660 feet, 7,500 ton Cantilever

14

Figure 1.20

Long Line Casting Form- San Francisco-Oakland

Figure 1.14

East Bay Skyway Bridge Figure 1.21

Figure 1.22 Figure 1.23

15

800-ton Segment Transporter- San Francisco Oakland East Bay Skyway Bridge

15

Segment Storage- San Francisco-Oakland East Bay Skyway Bridge

16

San Francisco-Oakland Skyway Bridge, Erection of First Segment, July 26, 2004

16

) Chapter 1.0 Introduction and Overview of Segmental Construction

2ofl7

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES 1.0 1.1

Introduction and Overview of Segmental Construction Purpose The purpose of this handbook is to provide guidance for construction of segmental concrete bridges. Although the segmental construction concept is generally very simple, the construction technology involved is in numerous ways more demanding than that required for other types of bridge construction. The use of segmental concrete bridge construction has grown rapidly, which has sometimes led to involvement of personnel with limited experience with segmental technology in the construction process. This handbook is intended to provide a basic understanding of segmental construction technology with the goal of facilitating the construction process, avoiding some problems previously encountered, and reducing delays and costs caused by concern over non-critical construction issues, or lack of understanding of critical issues.

1.2

Advantages of Segmental Construction Segmental concrete bridge construction offers the advantages of industrialized, repetitive construction procedures, which contribute to reductions in cost and construction time, as well as improved quality control. Segmental bridge construction offers maximum protection to the bridge environment, and provides for maintenance of highway and railway traffic at the construction site. Segmental bridges are easily adaptable to curved highway aligument and also provide aesthetic advantages. The advantages of segmental bridges have led to their widespread use for urban viaducts and interchanges, rapid transit bridges, bridges over water, and for very long bridges built using span-by-span construction. Finally, segmental construction extends the span range of concrete bridges to 550 feet using precast segments, and to over 800 feet using cast-in-place segments. Use of cable-stayed bridge construction (not covered in this handbook) permits the use of concrete segmental spans of more than 1,500 feet.

1.3

Structure Types

1.3.1

Precast Segmental Span-by-Span Precast segmental span-by-span bridges have normally been used for a span range of 80 to 150 feet. When segments can be transported by water spans of 180 feet are feasible. Span-by-span bridges provide very high speed of construction, and can be constructed over or parallel to existing highways with little or no impact on traffic. Span-by-span bridges are most often constructed using an erection truss under the segments as shown in Figures 1.1 and 1.2. Overhead erection gantrys have also been used for span-by-span construction.


3 of 17

Figure 1.1- Erection Truss in Place to Receive Segments

Figure 1.2- Erecting Segments on the Glenwood Canyon Project

J Chapter 1.0 Introduction and Overview of Segmental Construction

4 of 17

')

1.3.2

Precast Segmental Balanced Cantilever Bridges Precast segmental balanced cantilever bridges are presently used in the U.S. for spans up to 440 feet When circumstances permit the use of "heavy" segmental construction, spans as long as 820 feet have been built in balanced cantilever. The balanced cantilever construction process involves placing segments progressively on alternate sides of a pier. As shown in Figure 1.3, segments can be erected by land or barge-mounted cranes, by deck-mounted lifting equipment, or by an overhead gantry. Erection speed using cranes typically varies between 2 to 4 segments per day per crane. A mobile rubber-tired segment erector used in 2002 in construction of the Dallas High Five Interchange is shown in Figure 1.4.

'.' = II I

II I I I =

!

!

I

,.

I! l

''1''1'''1'1~

Figure 1.3- Common Segment 1nstallation Methods

)

Figure 1.4- Erection of Cantilever N-ES with Segment Erector. Cantilever W-N 10 in the Foreground


5 of 17

1.3.3

Precast Segmental Progressive Placement Precast segmental progressive placement may be used for spans ranging from I 00 to 300 feet. This method

of construction has been applied or considered in environmentally sensitive locations where construction access is restricted to one or both ends of the bridge. A sketch of the erection scheme is shown in Figure 1.5, and a construction view of the Linn Cove Viaduct is presented in Figure 1.6.

Figure 1.5- Erection Scheme for Progressive Placement

Figure 1.6- Construction of the Linn Cove Viaduct, NC


6 of 17

. \

1.3.4


I

Construction of the precast segmental arch spans of the Natchez Trace Parkway Bridge in Tennessee is illustrated by Figures 1.7 and 1.8. The arch spans range to 582 feet. Segment erection is supported by tiebacks to piers, or tie-backs anchored at ground anchors at the abutments. The Natchez Trace Parkway Bridge deck was constructed utilizing balanced cantilever construction with spans ranging from 90 to 246 feet.

Figure 1.7 - Construction of Natchez Trace Arch Bridge

Figure 1.8- Placement of Keystone of Natchez Trace Arch Bridge Chapter 1.0 Introduction and Overview of Segmental Construction

7 of 17

1.3.5

Cast-in-Place Segmental Balanced Cantilever Bridges Cast-in-place balanced cantilever bridges are used for spans ranging from 350 to 850 feet, although spans in excess of 700 feet are rare. Typical cast-in-place cantilever bridge construction is illustrated in Figure 1.9. As shown in the figure, the construction of cast-in-place cantilever bridges is based on the use ofform travelers which support the concrete for segments that typically vary between 10 and 20feet long, although longer lengths are possible. An average form traveler, for a single-cell box girder weighs approximately 160-180 kips. Extreme weights for large form travelers can exceed 250 kips. Typically, segments are constructed in each form traveler on a 5-day cycle. However, 2-, 3- and 4-day cycles per segment have been achieved in some cases. As illustrated by Figure 1.9e, cast-in-place segmental construction utilizing tie-backs can be used for construction of segmental arches.

d)

Figure 1.9- Construction of Cast-in-Place Balanced Cantilever Bridges


8 of 17

1.3.6

Cast-in-Place Segmental Arches Cast-in-place segmental construction for the 535 feet arch span of the Crooked River Bridge in Oregon in 2000 is shown in Figure 1.1 0. A rendering of the Hoover Dam Bypass Bridge with a segmental arch span of 1,090 feet is presented in Figure 1.11. Construction of the Hoover Dam Bypass Bridge began in the Fall of 2004. The construction schedule calls for completion in June of 2008. The Hoover Dam Bypass Bridge design includes an alternate for precast segmental construction of the arches.

FiJ?ure 1.10- Construction of the Crooked River BridJ?e Arch, OR

)

Figure 1.11- Hoover Dam Bypass Arch Bridge Rendering


9 ofl7

1.3.7

Cast-in-Place Segmental Incremental Launching Cast-in-place segmental incremental launching involves construction of segments in a casting bed at one or both abutments, and pushing the segments across the piers by means of hydraulic jacks. Spans may range to about 350 feet, but longer spans may require use of temporary mid-span supports. The principle of incremental launching is illustrated in Figure 1.12. Figures 1.13 and 1.14 illustrate incremental launching of the Bellaire Beach Bridge in Tampa, Florida in 2008. Detailed description of construction of incrementally launched concrete bridges is presented in Chapter 6.0. A steel launching nose is attached to the first segment to reduce moments and stresses during launching as shown in Figure 1.13 with reference to the Bellaire Beach Bridge in Tampa, Florida. Launching equipment for the Bellaire Beach Bridge is shown in Figure 1.14.

l Figure 1.12 -Incremental Launching

Figure 1.13 -Launching Nose on Bellaire Beach Bridge, Tampa, FL (Photo courtesy of VSL)


10 of 17

Figure 1.14 -Launching Equipment for the Bellaire Beach Bridge, Tampa, FL (Photo courtesy ofVSL)

1.3.8

Precast and Cast-in-Place Segmental Cable-Stayed Bridges Precast and cast-in-place cable-stayed bridges are discussed in Chapter 7.0. In addition, both precast segmental construction technology and cast-in-place segmental technology as discussed in this Handbook are applicable to construction of concrete cable-stayed bridges. Examples of U.S. cable-stayed bridges are the C&D Canal Bridge in Delaware with precast segments and a main span of750 feet (Figure 1.15), the Sunshine Skyway Bridge in Tampa, Florida with precast segments and a main span of I ,200 feet (Figure 1.16), and the Dames Point Bridge in Jacksonville, Florida with cast-in-place segments (edge girder, deck and floor beam) and a main span of I ,300 feet (Figure 1.17).


11 ofl7

Figure 1.15- C & D Canal Bridge, DE

Figure 1.16- Sunshine Skyway Bridge, Tampa, FL


12ofl7

Figure 1.17- Dames Point Bridge, Jacksonville, FL

1.3.9

Heavy Segmental

1.3.9.1 Confederation Bridge, New Brunswick- Prince Edward Island, Canada For the Confederation Bridge between New Brunswick and Prince Edward Island, Canada, massive segmental cantilevers 660 feet long and weighing 7,500 tons were assembled at a casting yard adjacent to the bridge site (Figure 1.16), and erected by a huge floating catamaran in one piece (Figure 1.17).

)

Figure 1.18 - Confederation Bridge Casting Yard

Chapter \.0- Introduction and Overview of Segmental Construction

13ofl7

Figure 1.19- Erection of 660 foot, 7,500 ton Cantilever

\


14ofl7

1.3.9.2 San Francisco - Oakland East Bay Skyway Bridge The Skyway portion of the San Francisco Oakland Bay Bridge, East Span Replacement consists of dual precast segmental concrete structures, measuring 6,900 feet in length, and two times 82 feet in width. The typical span length is 525 feet, and 28 cantilevers will be constructed using 452 precast segments. Typical segments are 25 feet long, 82 feet wide, and the maximum segment weight is 800 tons. Figure 1.18 shows the long .line casting form for the segments, Figure 1.19 shows the 800-ton segment transporter, and segment storage is illustrated in Figure 1.20. Segments are delivered on barges since the entire structure is over water. The erection equipment consists of self-launching beams and hydraulic winches. The size and weight of these segments has made the design and fabrication of this erection equipment unique and challenging. All lifting and hydraulic equipment has been factory tested and calibrated. In addition, each SLED will be load tested to 125 percent of the heaviest segment weight. The Skyway Structure consists of 28 cantilevers, and each cantilever has up to nine segments on each side. The speed of moving from cantilever to cantilever is more important than the lifting and launching speed for each segment. The two lifters that make up a SLED are fully self-contained, and each lifter can be moved to the next cantilever in a single pick as a complete unit. Figure 1.21 shows erection of the first segment on July 26, 2004.

Figure 1.20- Long Line Casting Form- San Francisco-Oakland East Bay Skyway Bridge

) .. /

Figure 1.21 - 800- ton Segment Transporler- San Francisco Oakland East Bay Skyway Bridge Chapter 1.0 Introduction and Overview of Segmental Construction

15 of 17

Figure 1.22- Segment Storage- San Francisco-Oak/and East Bay Skyway Bridge

Figure 1.23 - San Francisco-Oakland Skyway Bridge, Erection of First Segment, July 26, 2004


16 of 17

1.4

Documentation of Design Assumptions In Contract Documents Adequate documentation of the assumptions made during the design phase regarding the construction methods and erection loads is essential to contractors. To deliver a cost effective and successful project, the construction sequence, schedule, methodology and equipment assumed during the design phase should be clearly and thoroughly presented in the contract plans. Maximum leeway for contractor modifications with regards to means and methods of construction should be provided in specifications; however, the basic system should be clearly presented to facilitate the receipt of accurate and responsive bids. Given the traditional method of separating design from construction, and further considering the relatively short bid preparation time, contractors must be presented with a scheme that works and has no hidden costs that become evident after the project has been awarded. Problems have occurred on segmental projects where construction loads were underestimated or misrepresented. The results were that the required strengthening of the permanent structure for temporary conditions led to additional costs and claims. When designing a segmental bridge, it is the designer's responsibility to outline the design, method of constructions f!Ild equipment used as the assumption for the design. With the assumptions clearly stated, the contractor tan re-engineer the structure, if need be, to suit his needs/experience with confidence, which leads to competitive bids.


17 of 17

)

)

TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 2.0 TERMINOLOGY 2.0 Terminology

3

2.1 General Terminology

3

2.2 Post-Tensioning and Grouting Terminology

8

) Chapter 2.0- Terminology

Page I of 10

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 2.0 TERMINOLOGY

Figure 2.1 -Segmental Bridge Components

5

Figure 2.2 - Segment Features

5

Figure 2.3- Diabolo Details

6

Figure 2.4- Deviation Trumpet Details

7

Figure 2.5 Tendon Details

10


Page 2 of 10

2.0 Terminology 2.1 General Terminology Anchorage Block- Build-out io the web, flange, or web-flange junction to provide area for one or more tendon anchorages (Figure 2.2). Balanced Cantilever Erection - This is an erection method where segments are erected alternatively on either side of the pier in cantilever up to the point where a cast-io-place closure is made with the previous cantilever or existing side span structure (Chapter 4.0) Beam and Winch - Custom made erection equipment consisting of a longitudinal beam fitted with lifting pulleys, tackle and winches which is attached to the end of a cantilever and lifts up the segments. After erecting a segment, the equipment is advanced for erection of the next segment. This equipment is used with balanced cantilever or progressive cantilever erection (Figure 4.3). Box Girder or Box Pier- Box shaped structural member used for bridge superstructures and piers as shown in Figure 2.2. Cantilever Tendons - Longitudinal post tensioniog installed in the top slab of segmental bridges built io balanced cantilever. Cast-in-Place Segmental Bridge- A Bridge constructed with cast-in-place segments. Casting Curve - This is the geometric profile to which the segments must be made in order to achieve the required theoretical bridge profile after all final structural and time-dependent (creep and shrinkage) deformations have taken place. Closure - Cast-in-place concrete segment or segments used to complete a span.

Continuity Tendons- Longitudinal post tensioning installed in the bottom slab of segmental bridges built io balanced cantilever. Diabolo - Details for continuous duct placement through deviation saddles, and for connection at diaphragms (Figure 2.3)

Deviation Saddle -Build-out in the web, flange, or web-flange junction to provide for change of direction of an external tendon.

Deviation Trumpet- Detail for tendon connection of deviation saddles and diaphragms to provide tolerance for angle of tendon connection (Figure 2.4). External Tendon - Tendon located outside the flanges or webs of the structural member, generally inside the box girder cell. Erection Truss Span-bv-Span - This is a custom built truss which rests underneath a span on supports connected to the pier and/or previously erected superstructure onto which a complete span of segments is

placed by crane or other device. Such trusses may be self launching to the next span or may be moved by cranes.

Form Traveler - Equipment utilized for construction of Cast-in-Place segmental bridges. Major components include the structural frames (horses), the upper work platform, the lower work platform, and the trailing work platform. The form traveler is used to advance the forms from segment to segment. It also supports the leading edge of the forms throughout the "form-rebar-pour" cycle.

Chapter 2.0- Terminology

Page 3 of 10

Launching Gantry - Custom built erection equipment which is used to take delivery of the segments, lift, move and place them in their fmal erected locations in the superstructure. After completion of a cantilever or span, the gantry is capable of launching itself forward into a position ready to construct the next cantilever, or span. Internal Tendon - Tendon located within the flanges or webs (or both) of the structural member. Long Line Casting - Method of casting segments on a long casting bed which makes up the complete cantilever or span between field closures. Match Cast- Method of casting segments whereby a segment is cast against an existing segment to produce a matching joint. When the segments are separated and re-assembled in the structure, the mating surfaces fit together and reproduce the "as cast geometry." Permanent Post Tensioning- Post tensioning that is required as part of the completed structure. Pier Table- The portion of a cast-in-place segmental bridge that is built atop the piers prior to assembly of the form travelers. In fact, a key factor in the pier table design process is the decision about whether to only provide space for assembly of one form traveler or to provide adequate space for concurrent fabrication of two form travelers. Precast Segments - Box shaped precast concrete elements which can be assembled to form a bridge superstructure or pier (see Figure 2.1). Precast Segmental Bridge - A bridge constructed with precast segments. Common types described in Article 1.3 of Chapter I. Progressive Erection in Cantilever - Segments are erected in cantilever in one direction only from one pier to the next using temporary intermediate piers or temporary cable stays or both to support the advancing cantilever. Segmental Constrnction - the fabrication and erection of a structural element (superstructure and/or substructure) using individual elements, which may be either precast or cast-in-place. The completed structural element acts as a monolithic unit under some or all design loads. Post-tensioning is typically used to connect the individual elements. For superstructures, the individual elements are typically short (with respect to the span length) box-shaped segments with monolithic flanges that comprise the full-width of the structure.

Short Line Casting - Method of casting each segment in a special form called a casting cell using a fixed bulkhead at one end and a previously cast segment at the other as shown in Figures 6.10, 6.11, and 6.12. The form is only one segment long, hence the term "short line. 11

Span-bv-Span Erection - This is an erection method where all the segments for one span are placed on a temporary support truss, aligned, jointed, and longitudinally post-tensioned together in one operation to make a complete span. See Chapter 3.0.

Temporary Post Tensioning- Post tensioning installed solely for erection purposes.

Transverse Tendons- Post tensioning installed in the top deck and perpendicular to the centerline of the bridge, typically to strengthen the cantilevered wings of the segments.


Page 4 of 10

Pier segment /Jiitphl'tiltin

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....._......----- ...

-~~-~-~--r~---~

"'"'· Lu»gitudiJl.tJI ~antJJe:w::r

past-le;nsinning T.rans1o>~r.se

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pot bearings

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Figure 2.1 -Segmental Bridge Components

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irl recess

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~~~~~~i~~~~~~~~s~;~~~:~~~:::J

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ftir lc:mporat'y

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Figure 2.2- Segment Features


Page 5 of!O

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Page 7 of 10

2.2

)

Post-Tensioning and Grouting Terminology

Anchorage Assembly- An assembly of various hardware components which secures a tendon at its ends after it has been stressed and, imparts the tendon force into the concrete (Figure 2.5). Anticipated Set- The wedge set assumed to occur in the design calculation of the post-tensioning forces at the time ofload transfer. Bar- Post-tensioning bars are high strength steel bars, normally available from 5/8 to 2 1/2 inch diameter and usually threaded with very coarse thread. Bearing Plate - Any hardware that transfers the tendon force directly into a structure or the ground. Bleed- The autogenous flow of mixing water within or its emergence from, newly placed grout, caused by the settlement of the solid materials within the mass. Bursting Force- Tensile forces in the concrete in the vicinity of the transfer or anchorage of prestressing forces.

Coupler- A device used to transfer the prestressing force from one partial length prestressing tendon to another. (Strand couplers are not permitted.) Deviation Saddle - A concrete block build-out in a web, flange, or web-flange junction used to control the geometry of, or to provide a means for changing direction of external, tendons.

Duct- Material forming a conduit to accommodate prestressing steel installation and provide an annular space for the grout which protects the prestressing steel.

Effective Prestress - The stress or force remaining in the prestressing steel after all losses (short-term and long-term) have occurred. Family of Systems- Group of post-tensioning tendon assemblies of various sizes which use common anchorage devices and design. All components within the family of systems shall be furnished by a single supplier and shall have a common design with varying sizes.

Fluidity- A measure of time, expressed in seconds necessary for a stated quantity of grout to pass through the orifice of a flow cone. Grout- A mixture of cementitious materials and water with or without mineral additives or admixtures, proportioned to produce a pumpable consistency without segregation of the constituents, when injected into

the duct to fill the space around the prestressing steel. Grout Cap - A device that contains the grout and forms a protective cover sealing the post-tensioning steel at the anchorage.

Heat Shrink- Heat welding techniques to make splices between sections of plastic duct, in accordance with the duct manufacturers instructions. Heat shrink sleeves having unidirectional circumferential recovery

manufactured specifically for the size of the duct being coupled consisting of an irradiated and cross linked high density polyethylene backing for external applications and linear-density polyethylene for internal applications.

Inlet (also inlet pipe or grout injection port) - Tubing or duct used for injection of the grout into the duct. Jacking Force - The force exerted by the device that introduces tension into the tendon. Outlet (also ejection pipe or grout outlet vent or vent)- Tubing or duct to allow the escape of air, water, grout and bleed water from the duct.


Page 8 ofiO

J

Post-tensioning- A method of prestressing where tensioning of the tendons occurs after the concrete has reached a specified strength. Pre-stressing Steel- The steel element of a post-tensioning tendon, which is elongated and anchored to provide the necessary permanent prestressing force. Post-Tensioning Scheme or Layout- The pattern, size and locations of post-tensioning tendons provided by

the Designer on the Contract Plans.

Prepackaged Grout- grout with anti-bleed, low permeability, and thixotropic characteristics Post-tensioning System -An assembly of specific models of hardware, including but not limited to anchorage assembly, local zone reinforcement, wedge plate, wedges, inlet, outlet, couplers, duct, duct connections and grout cap, used to construct a tendon of a particular size and type. The entire assembly must me'et the system pressure testing requirement. Internal and external systems are considered independent of one another. Pressure Rating - The estimated maximum pressure that water in a duct or in a duct component can exert

continuously with a high degree of certainty that failure of the duct or duct component will not occur (commonly referred to as working pressure).

Set (Also Anchor Set or Wedge Set) - Set is the total movement of a point on the strand just behind the anchoring wedges during load transfer from the jack to the permanent anchorages. Set movement is the sum of slippage ofthe wedges with respect to the anchorage head and the elastic deformation of the anchor components. For bars, set is the total movement of a point on the bar just behind the anchor nut at transfer and is the sum of slippage of the bar and the elastic deformation of the anchorage components. Special Anchorage Device- Anchorage device whose adequacy should be proven in standard acceptance test. Most multiple anchorages and all bond anchorages are special anchorage device. Strand- An assembly of several high strength steel wires wound together. Strands usually have six outer wires helically wound around a single straight wire of a similar diameter. Stressing Jacks and Gauges - Each jack will be equipped with a pressure gauge for deterruining the jacking pressure. The pressure gauge will have an accurate reading gauge with a dial at least 6 inches in diameter. Temporary Corrosion Protection- The introduction of a substance into the post-tensioning ducts subsequent to installation and stressing of post-tensioned tendons and prior to grouting for purpose of preventing or mitigating the initiation or propagation of corrosion of post-tensioned steel. Tendon - A single or group of prestressing steel elements and their anchorage assemblies imparting prestress forces to a structural member or the ground. Also, included are ducts, grouting attachments, grout and corrosion protection filler materials or coatings. Tendon Size - The number of individual strands of a certain strand diameter or the diameter of a bar. Tendon Type- The relative location of the tendon to the concrete shape, internal or external.

Thixotropic - The property of a material that enables it to stiffen in a short time while at rest, but to acquire a lower viscosity when mechanically agitated. Transfer- The operation of imparting the force in a pre-tensioning anchoring device to the concrete. Vacuum Grouting- grout injection used for repair of voids in ducts and anchorages after generating a vacuum in the void space.

Chapter 2.0- Terruinology

Page 9 of 10

Vacuum-assisted Grouting- normal grout injection after generating a vacuum in the duct containing the tendon.

Wedge Plate- The hardware that holds the wedges of a multi-strand tendon and transfers the tendon force to the anchorage assembly. (Commonly referred to as anchor head) Wedge- A small conically shaped steel component placed around a strand to grip and secure it by wedge action in a tapered hole through a wedge plate. Wire- A single, small diameter, high strength steel member and, normally, the basic component of strand, although some proprietary post-tensioning systems are made up of individual or groups of single wires.

Grout Inlet Grout Outlet

Grout cap Trumpet

Duct

Anchorage

3-part wedge

Strand

Figure 2.5 Tendon Details


Page 10 of 10

TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 3.0 CONSTRUCTION OF PRECAST SPAN-BY-SPAN BRIDGES

3.0


3

3.1

Introduction

3

3.2

Advantages of Segmental Span-by-Span Bridges

6

3.3

Typical Span-by-Span Erection Sequence

8

3.4

Special Considerations

17

3.5

Safety

18

3.6

Summary

20

)

) Chapter 3.0- Construction of Precast Segmental Span-by-Span Bridges

Page I of20

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 3.0 CONSTRUCTION OF PRECAST SPAN-BY-5PAN BRIDGES

Figure 3.1

Underslung Truss During Erection of Ernest Lyons Bridge

3

Figure 3.2

Underslung Truss During Erection of the Mid Bay Bridge

4

Figure 3.3

Overhead Gantry During Erection of Seattle Sound Transit Project

4

Figure 3.4

Overhead Gantry During Erection of the C&D Canal Bridge

5

Figure 3.5

Lifting an Entire Span of the Jamestown Bridge

5

Figure 3.6

Maintenance of Traffic for the Ernest Lyons Bridge Project

6

Figure 3.7

Maintenance of Railway Traffic for 1-11 0 Biloxi Project

7

Figure 3.8

Maintenance of Traffic for San Antonio Y Project

7

Figure 3.9

Advancing Trusses into Span to be Erected

8

Figure 3.10

Advancing Trusses on the MARTA Project

9

Figure 3.11

Erecting Segments onto Trusses

9

Figure 3.12

Erecting Segments at Lee Roy Selmon Crosstown Expressway

10

Figure 3.13

Erecting Segments onto Trusses at the Evans Crary Sr. Project

10

Figure 3.14

Erecting Segments on the Glenwood Canyon Project

11

Figure 3.15

Applying Epoxy for Joining of the Segments

12

Figure 3.16

Applying Temporary Post-tensioning for Epoxy Squeeze

13

Figure 3.17

Closure Joints and Draped Longitudinal Tendons

14

Figure 3.18

Casting Closure Joints

14

Figure 3.19

Stressing Permanent Post-tensioning

15

Figure 3.20

Stressing Crew working on a Stressing Platform

16

Figure 3.21

Typical Span-by-Span External Post-tensioning Tendons

16

Figure 3.22

Temporary Supports being Lowered After Span is Complete

17

Figure 3.23

Typical Conditions of Trusses After Erection of Final Span

18

Figure 3.24

Personnel Working Near Leading Edge with Safety Harness

19


Page 2 of20

3.0


3.1

Introduction Of all the types of segmental bridges, span-by-span bridges are possibly the simplest, and are often the most cost effective. They are typically utilized for moderate span lengths up to approximately 150 feet, although the construction method has been extended to spans upwards of 180 feet. For spans longer than approximately 150 feet to 180 feet, other erection methods typically become more attractive. Even at span lengths of 160 to 180 feet, span-by-span construction begins to lose much of its appeal. This is because the erection trusses become larger and the construction method begins to lose cost effectiveness. Serious consideration should be given to using span-by-span construction for any span length greater than 160 feet. Span-by-span construction can be defined as construction where an entire span is erected and becomes selfsupporting, before erecting the next span. Typically, this involves supporting an entire span of precast segments on a temporary erection truss. The segments are epoxy joined and the post-tensioning is stressed

to make the span self-supporting. The erection truss is then moved ahead to the next span and the erection process repeated. The erection truss (or trusses) most often supports the segments under the wings, or bottom soffit. Overhead erection trusses have also been utilized. Typical span-by-span construction can be

seen in Figures 3.1 and 3.2. There are several variations to the typical span-by-span construction method. Entire spans of precast segments can be constructed on the ground, or on barges, and then lifted into position. Similarly, entire spans can be cast-in-place on the ground, or on barges, and then lifted into position. (The lifting of an entire span can be seen in Figure 3.3.) It is also possible to utilize the previously completed spans to transport segments up the bridge deck and erect them from the "top-down". Another variation is to castin-place each span on the temporary erection trusses.

While many variations on the basic technique have been utilized, the common feature is that an entire span is erected and becomes self-supporting, before erecting the next span.

Figure 3.1 - Underslung Erection Truss during Top-Down Erection of the Ernest Lyons Bridge (Photo courtesy ofPCL Civil Constructors, Inc.)

Chapter 3.0- Construction of Precast Segmental Span-by-Span Bridges

Page 3 of20

Figure 3.2- Undendung Truss During Erection of the Mid Bay Bridge (Photo courtesy of Figg Engineering Group)

Figure 3.3- Overhead Gantry during erection of the Seattle Sound Transit Project (Photo courtesy of PCL Civil Constructors, Inc.)


Page 4 of20

)

Figure 3.4- Overhead Gantry during Erection of the C&D Canal Bridge (Photo courtesy of Figg Engineering Group)

Figure 3.5- Lifting an Entire Span of the Jamestown Bridge (Photo courtesy of Figg Engineering Group)


Page 5 of20

3.2

Advantages of Segmental Span-By-Span Bridges There are many advantages to precast segmental span-by-span construction, including: •

Low construction cost

• • •

High speed of construction Easy maintenance of traffic High durability

Of all the types of segmental construction, span-by-span constructed bridges are typically the most cost effective. Historically, precast segmental span-by-span bridges have competed successfully in alternate bids with cast-in-place concrete bridges, bulb-T bridges and steel bridges. Most of the work associated with span-by span bridges is done in the precasting operations. The precasting occurs in a casting yard and typically has no impact on highway or railway traffic occurring at the site of the new bridge. Once the segments are cast, span-by-span bridges can be erected quickly. This minimizes the time that construction impacts the site around the new bridge. It should be noted that traffic can be maintained under the temporary erection trusses, once they are in position for erection of a span. Typically the only restriction is that traffic is halted during the placement of each segment, which takes only a small amount of time (typically 15-30 minutes). Although traffic can be maintained under the trusses during erection, it should also be noted that care must be taken to protect vehicular traffic from epoxy squeeze. This can be accomplished using various methods, the most common

of which is using tarps that hang underneath the segments during the epoxy operation. Examples of traffic being maintained under and around spans being erected are illustrated in Figures 3.6 through 3.8.

Figure 3.6- Maintenance of Traffic for the Ernest Lyons Bridge Project (Photo courtesy ofPCL Civil Constructors, Inc.)


Page 6 of20

Figure 3. 7- Maintenance of Railway for I-1 10 Biloxi Project (Photo courtesy of Figg Engineering Group)

)

Figure 3.8- Maintenance ofRailway Traffic for San Antonio Y Project (Photo courtesy of Figg Engineering Group)


Page 7 of20

Segmental superstructures are highly durable for the following reasons. First, the entire superstructure is comprised of precast high performance concrete, cast in a controlled factory-like setting. Secondly the deck is post-tensioned in the transverse direction, which minimizes cracking of this most exposed of bridge structural elements. Finally, the superstructure is continuously post-tensioned in the longitudinal direction.

3.3

Typical Span-By-Span Erection Sequence The erection of a given span begins with moving the temporary erection trusses into position for erection of the span as is illustrated in Figures 3.9 and 3.10. For simple trusses, this is often accomplished with a crane to pull the trusses forward, or, more preferably, by a beam-and-winch system. More sophisticated trusses and overhead gantries are typically self-launching.

Closure Joint

Launching Truss

Figure 3.9- Advancing Trusses into Span to be Erected (Drawing courtesy of Figg Engineering Group)


Page 8 of20

Figure 3.10-Advancing Trusses on the MARTA Project (Photo courtesy of Figg Engineering Group) Once the trusses have been advanced to the next span, the segments are then loaded onto the trusses as illustrated in

Figures 3.11 through 3.14. Typically, all but one segment is loaded onto the trusses before epoxy joining begins. This is done because the truss deflections need to occur before the segments are epoxy joined, or else there is the

possibility that the deflections could crack a previously epoxied joint.

Figure 3.11- Erecting Segments onto Trusses (Drawing courtesy of Figg Engineering Group)


9 of20

Figure 3.12- Erecting Segments onto Trusses at Lee Roy Selmon Crosstown Expressway (Photo courtesy ofPCL Civil Constructors, Inc.)

Figure 3.13- Erecting Segments onto Trusses at the Evans Crary Sr. Project Chapter 3.0- Construction of Precast Segmental Span-by-Span Bridges

Page 10 of20

)

Figure 3.14- Erecting Segments on the Glenwood Canyon Project (Photo courtesy ofFigg Engineering Group) Figure 3.15 shows epoxy being applied to segments as a part of the joining process. Normally, temporary post-tensioning bars are used to apply the pressure for epoxy squeeze. These are often located in small anchor blocks located inside the segments, as shown in Figure 3.16. The number and location of temporary Tendon anchor blocks should consider the number of segments that can be glued at one time. Epoxy is typically applied to groups of segments that are then stressed together using temporary anchor blocks and post-tensioning bars. Even with slow-set epoxies, three to four segments may be a practical maximum before there is a risk that the epoxy will set before the group is stressed together. If the epoxy does set prior to stressing the temporary bars, costly repairs will be required.


Page II of20

Figure 3.15- Applying Epoxy for Joining of the Segments (Photo courtesy of Figg Engineering Group) When groups of segments are stressed together, a significant amount of epoxy squeezes out of all sides of the segment, including the top deck. If this epoxy is not swabbed down flush with the deck, problems could arise later in the project during the deck grinding operation (required by most specifications). Deck grinders will often only cut grooves through the hardened epoxy rather than completely remove it as one might think. This in turn causes the back wheels of the grinding machine to ride up onto the epoxy thus causing the front of the machine to grind deeper into the deck. A dip is then created in the traveling surface of the structure which is considered unacceptable by most standards. Swabbing of the epoxy on the top deck prior to it hardening will make deck grinding easier and ultimately produce a better product. Similarly, it is important to swab the insides of the permanent post-tensioning ducts of the pier segments after the epoxy operation. If epoxy squeezes into the post-tensioning ducts and swabbing is not performed, crews could have difficulty installing the permanent post-tensioning cables.


Page 12 of20

Figure 3.16- Applying Temporary Post-tensioning for Epoxy Squeeze (Photo courtesy of Figg Engineering Group) Once all but the final segment is in place and epoxied, the one remaining segment is installed, epoxy joined and temporarily stressed. Small concrete spacer blocks are then placed in the closure joints between the typical segments and the pier segments, and approximately 5 percent to 8 percent of the permanent longitudinal post-tensioning is stressed. This locks the geometry of the span in-place. It should be noted that the spacer blocks used to maintain the closure joint opening can either be precast concrete blocks or cast-in-place high strength grout blocks. If cast-in-place blocks are used, there are products on the market today that can achieve the required strength in approximately 2 hours. The closure joint concrete is then placed using high strength concrete, as illustrated in Figures 3.17 and 3.18. Closure joints are typically placed at the end of a shift to allow for curing of the concrete. Even using high early strength concrete, it can take 10-12 hours to achieve the required strength for stressing (depending on the ambient temperature). After the closure joints achieve a nominal strength (typically 2500 psi to 3000 psi), the longitudinal post-tensioning is stressed to the final force, as illustrated in Figure 3.19. Draped external tendons that run the length of one span and overlap across a pier segment with the tendons from the previous span (Figure 3.19) are commonly utilized to create continuous span units. It should be noted that construction loads (i.e. fully loaded concrete trucks, etc.) on adjacent spans

are sometimes prohibited until closure joints have been cured to a specified strength and final stressing is complete. This is often a requirement because construction loads in adjacent spans can cause vibration and movement to be transferred across the closure joint. If the closure joint has

not been properly cured, this vibration could jeopardize the structural integrity of the joint.


Page 13 of20

Closure Joints

Closure Joints

Temp. Supports

Figure 3.17- Closure Joints and Draped Longitudinal Tendons (Drawing courtesy ofFigg Engineering Group)

Figure 3.18- Casting Closure Joints (Photo courtesy of Figg Engineering Group)

) ~


Page 14 of20

Stressing of the permanent post tensioning tendons is usually performed from a specially fabricated stressing platform that is attached to the pier segment. The purpose of the stressing platform is to provide a safe access for personnel to efficiently perform stressing operations. The stressing platform is often equipped with chain-falls that are used to support the stressing jacks from above. Figure 3.19 shows a stressing jack being supported from above by a chain-fall during stressing operations.

Figure 3.19- Stressing Permanent Post-tensioning (Photo courtesy ofPCL Civil Constructors, Inc.) When designing a stressing platform, consideration should be given to the amount of working room required to thread the stressing jack over the strand "tails" extending from the anchor head. If the length of tails is not taken into account, crews will not have sufficient room on the platform to insert the strand tails into the jack without leaning over the edge of the platform, thus creating an unsafe condition. Figure 3.20 shows a stressing crew safely working on a stressing platform.


Page 15 of20

Figure 3.20- Stressing Crew working on a stressing platform

Figure 3.21- Typical Span-by-Span External Post-tensioning Tendons (Photo courtesy of Figg Engineering Group)


Page 16 of20

3.4 Special Considerations In order to ensure an efficient construction plan using the span-by-span method, it is critical that special attention be given to certain activities. For example, sufficient clearance must be allowed between temporary truss supports and the bottom of the completed structure to allow for removal of temporary supports. Figure 3.22 shows a temporary support being lowered through the completed deck above using steel rods.

Figure 3.22- Temporary Supports being lowered after span is complete

It is also important to consider how and when construction materials and equipment are placed inside the bridge structure. As with all segmental bridge construction, the span-by-span method requires a significant portion of the work to take place from inside the bridge structure. This work requires tools, equipment and materials to be transferred into and out of the bridge structure. Once

a span has been completed and the trusses have been advanced, it can be extremely difficult to place bulky materials such as HOPE ducts, strand, temporary post-tensioning bars, etc. inside the bridge structure. It is often easiest to place construction materials inside the bridge through the open end of the structure (leading edge of construction) when crews have access from the trusses and stressing platforms. Likewise, it is always best to dispose of waste materials as each individual span is

completed rather than waiting until the end of the project when access is not readily available.


Page 17of20

Finally, a well thought out plan must be in place to remove the erection trusses after the fmal span is complete. Many structures require that special erection sequences be used during the final span to allow for removal of the trusses. If the fmal span to he erected is at an abutment, blockouts may be required in the back wall to allow for permanent stressing or truss removal. Figure 3.23 shows a typical situation in which the trusses must be removed from underneath the structure with very little vertical clearance.

Figure 3.23- Typical Conditions of Trusses after Erection of Final Span

3.5

Safety Safety is of paramount concern for all types of bridge construction. In addition to the typical safety concerns on all construction projects, the span-by-span method of segmental bridge construction has several unique safety challenges of its own.

As with all segmental construction, the leading edge of the structure during span-by span construction is constantly changing. It is not uncommon for site conditions to change drastically within one shift. For this reason, it is essential that strict procedures be in place to communicate

all hazards and protect site personnel. While a span is being erected on the truss, it is common to require all personnel working on the individual segments to be tied off I 00% of the time. This becomes extremely critical during the epoxy joining operation when segments are being pulled together, thus creating gaps between adjacent segments. All employees working inside and on top of the segments during this phase must be tied off.

Once all segments have been epoxied together and all gaps have been closed, it is possible for personnel to work inside the bridge and on the top deck without being tied off, provided that all leading edges are properly delineated per OSHA guidelines. Figure 3.24 shows a typical situation in which personnel are required to work near a leading edge (note all workers have harnesses and

are tied off to cables anchored to the bridge deck).


Page 18of20

Figure 3.24- Personnel working near leading edge with safety harness In addition to fall protection, another safety concern includes procedures for post-tensioning the temporary and permanent post-tensioning tendons. Temporary post-tensioning bars and bar jacks used during the epoxy squeeze operation are often heavy and awkward and must be lifted very near the ceiling of the segment, many times in the corners. This activity is often very difficult and can easily cause back injuries or muscle sprains if not well planned. If possible, temporary stressing blocks should be designed to allow for easy access of personnel and equipment.

Permanent post-tensioning operations are performed using jacks with extremely high forces (in excess of 500 tons). As a result, personnel working around this operation should be well trained in the hazards associated with post-tensioning. For example, no personnel should be allowed directly behind either end of the post-tensioning tendons when the stressing operation is taking place, in case one or more strands should break. In addition, prior to starting the stressing operation, all personnel in the area should be made aware that the operation is underway so that they know to take the proper safety precautions. This is often communicated with a siren or an air horn. In addition to the above mentioned concerns, thought should also be given as to how the leading edge of the structure will be delineated after erection of a certain span is complete and the trusses have been advanced forward. Several other crews are required to follow behind the erection crew and it is important that the leading edges of the bridge structure be maintained until the permanent traffic barrier or railing is in place.


Page 19 of20

3.6 Summary Span-by-span constructed bridges are one of the most simple and cost effective forms of segmental construction. They have successfully competed in alternate bids with cast-in-place concrete bridges, bulb-T bridges and steel bridges. They are erected very rapidly. Due to the speed of erection, and the fact that traffic can be maintained under the erection trusses (except during times when segments are being placed on the truss), the use of span-by-span construction can result in significant savings in maintenance of traffic costs and reduction in user delays. Spanby-span bridges incorporate high performance concrete and a biaxially, post-tensioned deck, resulting in a very durable structure.

\

.) Chapter 3.0- Construction of Precast Segmental Span-by-Span Bridges

Page 20 of20

TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 4.0 CONSTRUCTION OF PRECAST BALANCED CANTILEVER BRIDGES

)

4.0 Construction of Precast Segmental Balanced Cantilever Bridges 4.1 Overview 4.1.1 Basics of the Technique 4.1.2 Typical Segments Configurations 4.1.3 Segment Details 4.1.3.1 Cantilever Tendon Anchorages 4.1.3.2 Continuity Anchors 4.1.3.3 Temporary Post-Tensioning 4.1.3.4 Permanent Ducts 4.1.3.5 Web Keys 4.1.3.6 Flange Keys 4.2 Casting Yard and Transportation 4.2.1 Forms 4.2.2 Detailing and Workmanship 4.2.3 Geometry Control 4.3.4 Lifting Details 4.3 Typical Erection Cycle 4.3.1 Overview 4.3.2 Epoxy 4.3.3 Temporary PT 4.3.4 Tendon Installation and Jacking 4.3.5 Grouting 4.4 Erection Equipment and Methods 4.4.1 Crane 4.4.2 Beam and Winch 4.4.3 Erection Gantry 4.4.4 Hauler 4.5 Special Topics 4.5.1 Surveying and Deflections 4.5.2 Pier Segments 4.5.2.1 Cast-in-Place 4.5.2.2 Precast Pier Segment 4.5.2.3 Precast Shell 4.5.3 Expansion Joints 4.5.4 Mid-Span Closure 4.5.6 Temporary Access Openings 4.6 Engineering 4.6.1 Built-in Loads 4.6.2 Erection Loads 4.6.3 Cambers and Deflections 4.6.4 Temporary Post-Tensioning

Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

3 3 3 4 5 6 7 7 7 9 9 9 9 10 13 13 14 14 15 16 17 18 19 20 21 22 27 27 27 28 28 30 31

33 37

38 38 38 39 39 39

Page I of39

TABLE OF FIGURES

)

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 4.0 CONSTRUCTION OF PRECAST BALANCED CANTILEVER BRIDGES Figure 4.1-1 Figure 4.1-2 Figure 4.2 Figure 4.3 Figure 4.4 Figure4.5 Figure 4.6 Figure4.7 Figure 4.8 Figure 4.9 Figure 4.10 Figure 4.11 Figure 4.12 Figure 4.13 Figure 4.14 Figure 4.15 Figure 4.15A Figure 4.16 Figure 4.17 Figure 4.18 Figure 4.19 Figure4.20 Figure 4.21 Figure 4.22 Figure 4.23 Figure 4.24 Figure 4.25 Figure 4.26 Figure4.27 Figure 4.28 Figure 4.29 Figure 4.30 Figure 4.31 Figure 4.32 Figure4.33 Figure4.34 Figure 4.35 Figure 4.36 Figure 4.37 Figure 4.38 Figure 4.39 Figure 4.40 Figure 4.41 Figure 4.42

Three Span Example, 1 of 2 (Courtesy of URS) 4 Three Span Example, 2 of 2 (Courtesy of URS) 5 6 Wide Cross Sections (Courtesy of URS) Bulkhead Details 7 Anchorage Configurations (Courtesy of URS) 8 Typical Tendon Layout 9 Typical Form and Fixed Bulkhead 11 Detailing 1 12 12 Detailing 2 12 Detailing 3 Detailing 4 13 Detailing 5 13 Casting Direction 14 15 Typical Lifting Methods (Courtesy of URS) 15 Typical Erection Cycle Epoxy Application 16 16 Epoxy Protection Temporary PT Blisters 17 Internal Temporary PT (Courtesy of URS) 18 Stressing Platforms on the Otay River Bridge (Courtesy of Otay River Constructors) 19 Common Erection Methods (Courtesy of URS) 20 Segment Erection by Crane on PR181 (Courtesy of Las Piedras Construction) 21 Deck Mounted Crane Erection- Sound Transit Tukwila Line 22 Beam and Winch Erection (Courtesy of KiewiVFiatiron/Manson JV) 22 23 Mobile Lifter, Dallas Hi-5 (Courtesy of DEAL) 24 Erection Gantries (Courtesy of URS) Segment Rotated 90 degrees Between Truss Chords 25 Erection Gantry Launched Forward (Courtesy of Otay River Constructors) 26 Self-Launching Dual Erection Gantry (Courtesy of 27 Trader Construction Corp.) Launching Gantry for Hanging Lake Viaduct (Courtesy of Flatiron Construction Corp.) 28 Cast-in-Place Pier Segment, Otay River Bridge 29 First Precast Segment Supported Prior to Casting Closure Joint (Courtesy of Parsons) 30 Blockout for Ducts at Construction Joint (Courtesy of Parsons) 30 Placing Precast Pier Segments (Courtesy of Las Piedras Construction) 31 Methods for Additional Stability (Courtesy of URS) 32 Precast Shell Installation 32 Installation of Precast Shell, Vancouver Millennium Line (Courtesy of DEAL) 33 Installation of Supplemental Rebar inside Precast Shells (Courtesy of DEAL) 34 Quarter-Span Hinge Erection Sequence 35 Quarter-Span Hinge Installation, H3 Viaduct 35 Mid-Span Hinge Schematic 36 Mid-Span Beam Installation (Courtesy of Parsons) 37 Column Expansion Joint Erection Schematic 38 Strongback Beams at Closure Joint Pour (Courtesy of Las Piedras Construction) 39

) Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 2 of39

4.0

Construction of Precast Segmental Balanced Cantilever Bridges

4.1

Overview

4.1.1

Basics of the Technique While precast balanced cantilever construction shares many features of precast segmental span-byspan construction, it is a distinct construction method that requires a unique set of details and

procedures. In balanced cantilever construction, erection progresses outwards from a central pier, until adjacent cantilevers meet at mid-span. Segment erection generally progresses by erecting symmetric pairs of segments, with one segment of each pair secured on opposite ends of the previously completed structure with post-tensioning bars. Each pair of segments is then stressed against the structure with cantilever tendons. These tendons are located in the top flanges of the segments, and run from one cantilever tip to the other. As segments are added, the cantilever tendons become progressively longer. A typical sequence for a three-span bridge is illustrated in Figure 4.1.

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Page 3 of39

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Figure 4.1-2- Three-Span Example, 2 of2

Balanced cantilever spans are generally considered in situations where span-by-span erection is impractical. Span lengths greater than 150' are typically prohibitive for span-by-span construction, while precast balanced cantilever construction is effective for span lengths from !50' to 450', and has been implemented for spans in excess of 500' in response to special circumstances. Balanced cantilever construction is well adapted for alignments with tight curvature. Erection gantries used for span-by-span erection, and particularly underslung gantries, may not be able to simultaneously place an entire span when the transverse offsets due to curvature are significant. With balanced cantilever erection, segments are placed individually, bringing more flexibility and extended reach.

4.1.2

Typical Segments Configurations The majority of balanced cantilever construction is performed using a single-cell trapezoidal box girder. Most of the examples and illustration in this section will focus on this configuration for the sake of simplicity. However, single-cell sections are limited to a width of about 60', and several different methods have been successfully implemented to achieve wider bridge decks. Examples are shown in Figure 4.2.


Page 4 of39

~ooro MULTI-CElL BOX

G ,_

14

SECTION A-A

~Rib 14

SECTION 8-8

SJNGlE-<:ElL BOX WITH TRAJISVERSE RIBS

SECTION

SINGlE -<:ElL BOX WITH STRUTS

\~

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PARAlLEL SINGlE-CElL BOXES

SECTION D-D

Figure 4.2 - Wide Cross Sections

4.1.3 Segment Details There are several features common to precast balanced cantilever segments that are best illustrated by examining a typical bulkhead drawing shown in Figure 4.3. The notable features include:


Page 5 of39

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Figure 4.3 -Bulkhead Details

4.1.3.1

Cantilever Tendon Anchorages.

These anchor the cantilever tendons that permanently secure each pair of tendons to the cantilever. They are typically located in the top flange, in close proximity to the web/flange junction. There are several different configurations for locating the cantilever tendons, illustrated in Figure 4.4. Considerations for choosing the location of an anchorage include the maximum tendon size, thickness of the top flange, interference with web stirrups, and cost and complexity of the forms. An additional consideration that is growing in importance is the role of grouting and anchorage protection. This area has seen new developments in recent years, and it is important that the anchorages are detailed to accommodate the project grouting, inspection and anchorage protection requirements.

Chapter 4.0 -Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 6 of39

Top Slab CantflwtJf Tendrm

" - Cantllwer Tendon

Blister~ Bottom Slab ~

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Top Slob ContiiENer Tendon

Contlfwer Tendon

Contloolfy Tendon

Figure 4.4- Anchorage Configurations

4.1.3.2

Continuity Anchors.

When two cantilevers are joined, continuity tendons are stressed across the completed construction joint. At this stage, there is no access to the segment face, so the continuity tendons are anchored in internal blisters. These are concentrated in the bottom flange, at the web/flange interface. Often there are a limited number of continuity tendons in the top flange as well.

4.1.3.3

Temporary post-tensioning.

During a typical erection cycle, the segments are secured against the cantilever with post-tensioning bars until the permanent tendons have been stressed. The various methods of accommodating these bars are discussed below, but it is important that they are anticipated from the earliest stages.

4.1.3.4

Permanent ducts.

Precast segments for balanced cantilever construction are notable for the number of holes on the face of the segment. Because each cantilever tendon stretches from end to end of the cantilever, segments near the pier must accommodate nearly one set of tendons for each segment in the cantilever. Figure 4.5 illustrates a typical longitudinal post-tensioning layout, showing the concentration of tendons in the top flange near the pier, and in the bottom flange near mid-span.


Page 7 of39

PLAN VlEW

Figure 4.5- Typical Tendon Layout

Balanced cantilever construction relies primarily on internal tendons, and attention to detail in the planning stages can simplify construction. In some cases, the contractor is permitted to adjust tendon layout and local details provided the post-tensioning force and eccentricity is maintained. Some typical considerations include: I.

Proper spacing of the ducts. Duct spacing is governed by the requirements of the AASHTO Specifications. and deserves careful attention. Ducts that are spaced too closely together are at an increased risk of a pull-through failure where transverse deviations occur. Ducts should be spaced at least one duct diameter apart. This limitation is generally increased, due to practical considerations. Duct holes in the bulkhead need W' or more between them to facilitate bulkhead manufacture and segment production.

Duct spacing is also important to prevent grout communication between ducts. It is also structurally necessary to have sufficient concrete between ducts to ensure proper transverse bending behavior in the top flange before the ducts are grouted. 2.

Ducts should be straight across all joints. When the segments are match-cast, an important consideration is alignment of the ducts across the segment joint. This is generally achieved by inserting a short, rigid mandrel in the ducts that cross the joint. When a duct is curved, a smooth transition is difficult to achieve, and can lead to unwanted kinks at the joint. It is frequently necessary to include tendons that run at a slight angle to the bridge axis. This is easily accommodated- it is only a curve that is to be avoided.


Page 8 of39

4.1.3.5

3.

Tendon and anchorage details should be standardized to the greatest extent possible. Duct placement is sometimes in areas with complicated and congested reinforcement, and standardized details are helpful in reducing conflicts and errors. Anchors generally require a small blockout behind the anchor plate to accommodate the geometry of the anchorage. If the orientation of the anchors can be standardized to one or two positions, the production efficiency is increased, and opportunities for confusion are eliminated.

4.

The integration of longitudinal ducts with transverse tendons should not be overlooked. The need for transverse tendons to avoid all longitudinal ducts can have an impact on the transverse.deck design.

Web keys.

Shear keys are indentations along the mating faces of the webs. Their purpose is to ensure the transfer of shear across the segment joint. As such, they should cover as much of the web as is achievable. 4.1.3.6

Flange keys.

Alignment keys are generally located in the top and bottom flanges of the segment. They are distinct from web keys, in that they are not explicitly designed to transfer global shear across the joint. Rather, their primary function is to ensure a proper fit-up between segments when they are erected in the field. They are also important in transferring local shear in the top flange at the joints. Balanced cantilever segments typically have large portions of the top and bottom flanges reserved for longitudinal ducts, so consideration should be given in design and construction to accommodating both ducts and alignment keys.

4.2

Casting Yard and Transportation

4.2.1 Forms As for most precast segmental construction, the casting cell bulkhead is a critical part of the set up. The basics of the bulkhead are covered elsewhere in this handbook, but there are a few features specific to balanced cantilever bridges that are worth noting. When span lengths are over 200 feet, it is frequently more cost effective to use a variable depth superstructure. This helps to provide peak shear and bending capacity where it is needed most. At the same time, it adds a layer of complexity to casting operations. Forms created for variable depth segments need to accommodate changes in depth, and to do so without interrupting the casting schedule. Common solutions include two-piece bulkheads, where the bulkhead can be lengthened or shortened by bolting together different pieces, adjustable soffit tables, and adjustable core forms. While one set of forms can accommodate a range of depths, it may be economical to have one set of forms that can accommodate the deepest segments, and another set to accommodate the shallowest. In this case, it is important to analyze the workflow to ensure the forms work together without interruption. While the fixed bulkhead is an important part of any casting cell, for a balanced cantilever bridge it takes on additional significance as the template for all longitudinal post-tensioning. All tendon ducts are secured to pre-existing holes in the bulkhead. This means that the bulkhead must include a hole at every location where a tendon crosses the joint- not just for that particular joint, but for all joints. It is beneficial to standardize and re-use duct locations in a post-tensioning layout, to

avoid unnecessary or overlapping holes in the bulkhead.


Page 9 of39

Figure 4.6- Typical Form and Fixed Bulkhead

Balanced cantilever designs make use of internal blisters for anchoring continuity tendons and temporary PT. While it is good to standardize the blister locations whenever possible, it is likely that the locations of internal blisters will vary. Core forms should be able to accommodate the addition or removal of an internal blister on a regnlar basis.

4.2.2 Detailing and Workmanship Proper attention to detail and good workmanship are always critical, but the stakes are raised in precast construction. Problems that would affect the structure during erection may not be discovered until much of the superstructure has been cast, and remedial action made more expensive. Many of the detailing issues for balanced cantilever segments are directly related to successfully integrating the internal tendons. Tendons can exert a significant force on the section wherever they deviate, be it by design or unintentional. Good workmanship is important in these areas. The topics listed below represent a partial list of areas specific to balanced cantilever bridges that merit close attention.

) Chapter 4.0 -Construction of Precast Segmental Typical Balanced Cantilever Bridges

Pagel0of39

The first location is where the ducts cross the segment joints. At this location, the two primary requirements are to create a smooth transition across the joint, and to eliminate the natural tendency for the ducts to sag (see Figure 4.7). The first is generally achieved by inserting a mandrel in the ducts of the match cast segment, which serves to align and seal the ducts. The second is achieved by ensuring the duct is firmly supported against the rebar cage at close intervals to as to maintain the duct in a tangent alignment at the joint.

BOTTOM FLANGE- SECTION

Figure4.7

Adequate duct support is important in other areas as well. One example is in the bottom flange, where continuity tendon ducts run the length of the segment. If the concrete is placed in a manner that requires a transverse flow (from web to centerline), ducts that are not adequately secured will tend to bow (see Figure 4.8). This can create small kinks at the bulkhead, where the duct is firmly attached. In general, proper duct support is the key to avoiding unwanted kinks.

-~"'=.," """""'
Figure4.8

Another area that requires particular attention is the toe of the anchorage blisters. This region typically includes a relatively tight curvature of the continuity tendon anchored in the blister (see Figure 4.9). As the tendon deviates, it exerts a radial force on the concrete, effectively trying to straighten. This deviation must be fit to the proper radius (not kinked) and tied back into the segment flange to avoid cracking. While it is the responsibility of the designer to provide adequate steel for this force, care should also be taken in the casting yard to ensure that the steel is well distributed along the full length of the deviation, and that the duct profile closely matches the radius shown in the plans. It is good practice to ensure that the curved portion of


BOTTOM FLANGE- SECTION

Fif!ure 4.9

Page II of 39

the duct is contained entirely within the toe of the blister, and it is important that the duct placement in the yard matches this requirement, when applicable.

HALF SE:Cr/ON

Figure4.10

The presence of numerous internal tendons raises the potential for certain types of delamination, where the tendon force causes a portion of the flange to peel away from the segment. The first is in the upper and lower flanges, where segments near the pier segment or midspan contain multiple closely spaced ducts. This translates to a significant portion of the flange that is effectively voided during erection, as grouting is generally not performed until the cantilever is complete. This is often mitigated by including "J" ties to secure the top and bottom mats of rebar (See Figure 4.1 0). These ties are typically evenly distributed along the length of the segment. Care should be taken to

place and develop any such ties as indicated on the plans.

Another area where delamination may occur is in the bottom flange of variable depth segments. The change in angle at the segment joint creates a natural deviation in the bottom flange tendons. This deviation has a tendency to pull out, delaminating the bottom flange. Supplemental stirrups are required in the vicinity to restrain the deviating tendons. A common configuration is shown in Figure 4.11. While seemingly minor, these stirrups play an important role and must be placed correctly.

Figure 4.11 These examples of common critical details do not constitute an exhaustive list. It is important that good engineering judgment be used in developing segment details, and that critical details are clearly shown in the plans and accurately implemented in the casting yard. Specific requirements for many of these details are given in AASHTO Specifications, their successful implementation begins with careful detailing during design.

J Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 12of39

4.2.3 Geometry Control In most respects, geometry control for short line casting is no different for balanced cantilever spans than it would be for any other precast span as discussed in Chapter I 0. There is one minor difference, however. Casting of balanced cantilever spans progresses from the pier to the cantilever tip. This means that the casting direction reverses for up- and down-station cantilevers. This is easily achievable, but requires additional care and attention to detail in determining casting coordinates, setting up the geometry control program, and determining the nomenclature for the casting coordinates. It is good practice to use a three dimensional CADD program to plot the casting coordinates for the entire bridge together, to check for any unintended kinks or

misalignments.

Figure 4.12- Casting Direction

4.3.4 Lifting details Many schemes have been developed for lifting segments for transport, some of which are illustrated in Figure 4.13. A common feature of many of these schemes are the holes in the top flange used to secure the lifting devices. For balanced cantilever segments, it is often difficult to identify a single lifting hole arrangement that will always avoid the cantilever tendon ducts in the top flange. It is preferable to design the lifting equipment at both the casting yard and erection site to accommodate a reasonable variation in pick points. It should be noted that sling supports are generally not compatible with balanced cantilever erection. This is because the segment has to be supported by the lifting equipment when the joint is closed. Also note that options 2 and 3 require

access outside the box for rem ova] during erection.


Page 13 of39

JJ Tcp s!ab S!JWJfl&i,!n carrt/lwers

Figure 4.13 - Typical Lifting Methods

4.3 Typical Erection Cycle 4.3.1 Overview \

Balanced cantilever erection is based around a standard two-segment cycle. The cycle begins when the first segment is lifted into position at the tip of the cantilever. Epoxy is applied to the segment face(s) immediately before they are joined together. The new segment is stressed against the existing structure by post-tensioning bars. These steps are repeated on the opposite end of the cantilever with the second segment. Cantilever tendons are stressed and anchored at the ends of the cantilever. At this point, the cycle begins again.

Figure 4.14- Typical Erection Cycle


Page 14of39

4.3.2 Epoxy Epoxy is now required for all segment joints, and has always been an AASHTO requirement for joints with internal tendons. In many jurisdictions, epoxy is required on both faces of the segments to be joined. The main purposes of the epoxy are to provide a strong, impermeable seal at the joint to prevent corrosion in the tendons, and to lubricate the joint during installation. For balanced cantilever construction, the epoxy can enter many of the empty ducts when the segments are stressed together if adequate measures to protect the duct are not taken. It is important to swab the ducts after erecting each segment, otherwise the epoxy can block the duct and hinder tendon installation for subsequent segments.

Figure 4.15- Epoxy Application

In addition, it should be noted that epoxy will frequently be squeezed out of the joint when the segments are initially stressed together with bars. It is likely that the uncured epoxy will drip from the bridge, both onto the ground and into the box interior. Precautions may be necessary to prevent epoxy from reaching the ground, for example in construction over active roadways or environmentally sensitive areas.

Figure 4.15- A Epoxy Protection

_) Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 15 of39

)

4.3.3 Temporary PT Temporary PT is generally a necessary part of a typical erection cycle. In most cases, the temporary PT will take the form of high-strength bars placed near the top and bottom flanges. The purpose of the temporary bars is twofold. First, they provide a means of securing the new segment to the cantilever, so that it may be released from the lifting equipment. Second, it provides a means of compressing the wet epoxy. The epoxy should be compressed to a minimum of 40 psi during the cure time, which can vary depending on product and temperature. The post-tensioning bars should provide a minimum compression both while the segment is supported only by the bars, and when the cantilever tendons have been stressed. There are three main methods of incorporating the temporary PT into the segment. The first is via small blisters cast on the interior of the box girder. They are typically located as shown in figure 4.16. This option allows easy access to both ends of the bars, so the bars can be removed andreused on later cycles. To be re-used, the bars must be stressed to a fairly low level, typically 50% of their ultimate strength. This method is very efficient during construction, and requires a limited quantity of bars. However, the forms and casting operations see a small impact due to the

inclusion of interior blisters.

Figure 4.16- Temporary PT Blisters The second method consists of using internal PT bars, incorporated into the segment cross section. Subsequent bars are coupled onto the previous set, and cannot be removed. Since the bars are permanent, they can be stressed to higher levels, and can be included in the design of the final structure. They must also be properly grouted and protected against corrosion. This method eliminates the need for internal blisters, which is beneficial for the casting yard. However, a greater number of bars is required.


Page 16 of39

Temporary PcstTenslonlrq Bar (lyp)

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Figure 4.17- Internal Temporary PT

The third method consists of using a bracket attached to the segment to anchor the bars. This functions much like the first option, but eliminates the blisters from the interior. However, careful attention must be paid to proper detailing of the brackets to avoid local spalling. Some operations are added to the typical cycle to secure the brackets in place for each segment.

4.3.4 Tendon Installation and Jacking In many ways, tendon installation is no different than a typical bridge. However, there are a few features that set balanced cantilever construction apart. The first is the frequency of tendon installation and stressing. With each cycle, at least two, and occasionally four or six tendons must be installed and stressed. This is a critical path activity, as the next pair of segments cannot be placed until the previous tendons have been completed. In some cases, three or four cycles are completed in a day, a rate that requires efficient posttensioning operations. Another is the location of the work. During cantilever construction, all of the post-tensioning installation and stressing is done from the end of the cantilever. In order to access the anchor heads, it is necessary to have post-tensioning platforms that provide access to each end of the cantilever. This platform must be removed and re-positioned with every cycle. Early efforts to integrate the stressing platforms with segment placement equipment and operations can have a positive impact on the speed of a typical cycle.


Page 17of39

Figure 4.18- Stressing Platforms on the Otay River Bridge

4.3.5 Grouting There is a growing recognition of the important role that grouting procedures play in the long-term performance of segmental bridges. For a balanced cantilever bridge, it is beneficial to refine the typical grouting operations. As noted above, tendons are installed and stressed on a daily basis during cantilever erection. However, it is generally best to wait until the entire cantilever is complete before grouting any of the cantilever tendons. This is because there is often an empty duct directly adjacent to each tendon when it is installed. If that tendon were grouted, there would be a risk of the grout crossing over to the empty duct. This would result in blockages when later tendons are installed if the empty ducts are not swabbed clear with each grouting operation

Depending on erection speed and local conditions, the allowable period for leaving a stressed tendon ungrouted may be exceeded. In this case, a corrosion inhibitor can be used to extend the period before grouting. In all cases, care should be taken to assure that water is not allowed to stand in the ducts during cantilever erection. In cases where roadway grade does not provide convenient drain points, grout inlets can be used to verify conditions in ungrouted tendons and blow out standing water if necessary.

Cantilever tendons are often very long and flat, with little variation in elevation other than roadway grade. This means that there are few high or low points where grout vents would be required. For longer tendons, it is worthwhile to install supplemental grout vents along the length of the tendons to improve grouting results.


Page 18 of39

4.4

Erection Equipment and Methods The defining task of balanced cantilever erection is delivering segments to the cantilever tip. The equipment chosen for this operation can have an important impact on the project cost and schedule. The three most common methods are with a crane, beam and winch, and erection gantry. Factors that can influence the choice of equipment include: • • • • • • •

Up-front cost Operating height Lifting capacity Terrain I Access Required safety factors (for example, when crossing a railway) Erection sequence Loads on the structure

•

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Page 19 of39

4.4.1 Crane Under the right circumstances, cranes can be used to place segments at the cantilever tips. This can be a very cost-effective option, as cranes are readily available. It also allows the possibility of erecting multiple cantilevers at once, offering savings on schedule.

However, the main constraint on crane erection is access. Balanced cantilever bridges are often selected in response to inaccessible terrain, be it over a highway, water, or an environmentally sensitive area. Since the crane will be used to place the segments in their final position, it must have access along the entire alignment.

Figure 4.20- Segment Erection by Crane on PR181

In some cases, this can be avoided by using a light crane positioned on the bridge deck. A ground based crane can be used to place segments on the deck, typically at the pier. The deck mounted crane then picks up the segments and carries it out to the tip. This technique was used on the Sound Transit balanced cantilever spans (Figure 4.21), and is generally only available for relatively light sections.


Page 20 of39

Figure 4.21 -Deck-mounted Crane Erection, Sound Transit Tukwila Line

4.4.2 Beam and Winch In this method, a beam and winch system is placed on each end of the cantilever. The segment is delivered below the tip, and the beam and winch lifts it into position. This option is often selected over water, where a custom built system can accommodate heavier segments. A notable example

of this is the San Francisco-Oakland Bay Bridge Approaches, pictured in Figure 4.22.

Figure 4.22 - Beam and Winch Erection


Page 21 of39

Some considerations for beam and winch systems include the access and the height. For a fixed system, access is required at every location along the alignment to deliver segments to the tip. In addition, hoisting segments over significant heights can be time consuming, and have a negative impact on the erection cycle. Some specialized equipment has been built to overcome these difficulties. Specialized lifters are able to move along the deck to hoist segments at an accessible location. They then deliver the segment to the cantilever tip for erection. These are generally custom built to suit a specific project. An example is the lifter used in the Dallas High-5 project, shown in Figure 4.23 below. It should be noted that this method may present some engineering challenges during erection, since the loaded hauler will occupy many different positions. Supplemental methods of reducing demand on the substructure, such as tie-downs or counterweights may be necessary.

\'

Figure 4.23 -Mobile Lifter, Dallas High-S

4.4.3 Erection Gantry Segmental construction is often chosen in response to limited access on the ground. This often drives the choice of erection method away from beam and winch or crane systems. and towards an erection gantry. The gantry enjoys the advantage of being able to work from the top down, with segments delivered over the completed spans. It can offer external stabilization for out of balance moments. which over the length of major structures can be a significant cost savings. Segments can also be lifted directly from the ground (or water) where conditions allow access. Site factors which may influence the decision concerning gantry use are the degree of horizontal curvature and the maximum grade which the gantry will be required to accommodate. Because the gantries in use today have evolved to a rather high level of sophistication and are genera1ly customized for a particular project, they represent a major investment in equipment. Their successful use is governed by the job's capacity to offset the up-front cost. This may be through increased speed of erection or in overcoming access restrictions. It is apparent that the cost impact of the gantry is reduced as the overall cost of the project becomes larger. Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 22 of39

The impact of schedule may also be a deciding factor in selecting an overhead gantry. Where the structure is relatively long and there is a reasonable repetitiveness of spans, a gantry can be a fast and efficient means of erecting cantilevers. However, gantries are restrictive, in that they impose a linear erection sequence on the project. It is not possible for a single gantry to erect on multiple piers, as would be the case with crane erection. With many of the gantries currently being designed and/or fabricated overseas, other issues should be considered including lead time, import challenges, quality control issues, design criteria and standards, replacement parts and equipment training.

~ -~ Rear Support

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Figure 4.24- Erection Gantries

After the pier segment is in place, either by setting it if precast or by casting it in place, the overhead gantry is positioned as shown in Figure 4.24 to begin typical segment erection. The gantry rests on two supports and is, therefore, statically determinate. The center support is anchored on the pier segment where the cantilever is being erected while the rear support is tied down at some point on the previous cantilever. The segments to be erected are either transported from the rear of the gantry along the completed structure or lifted directly from below depending on the conditions of ground or barge access at the site. In the former case, the gantry supports must be transversely spaced such that a segment, when rotated 90° to the bridge, may pass between them. A trolley which generally rides on the upper or secondary chords of the launching girder is used to transport the segment and to position it for erection.


Page 23 of39

\ Figure 4.25- Segment Rotated 90" between Truss Chords, Otay River Bridge After erection of a particular cantilever is completed and any span closures are made, the gantry is launched to begin cantilever erection on the following pier. The exact sequence involved depends largely on the gantry being used and the span configuration of the bridge under construction. If the gantry is of sufficient size relative to the forward span length, shown in Figure 4.24A, it may be possible to place the pier segment for the next cantilever without changing the longitudinal positioning of the gantry. If the nose section of the gantry is shorter than the forward span length as shown in Figure 4.24B, some sort of two-stage launch or temporary intermediate bent must be used. After the pier segment is in position, the gantry can be advanced until the central support is located over the pier segment. The support is then anchored to the pier to begin the next cycle of typical segment erection on the new cantilever.

The method by which a launching gantry advances relative to the bridge depends on the overall design of the gantry and the particular construction application. In some designs, the gantry is supported on temporary front and rear supports, and then prepared to launch by freeing the primary (center) support. The gantry rolls over the front (nose) support by means of a trolley fixed to the support. It may also roll over a similar trolley on the rear support, which has typically already been advanced and reattached to the deck near the center support. Alternately, for this type of gantry the rear support may be attached to the launching gantry itself. In this instance the rear support would actually roll over the completed deck on rubber tires or a rail system. In other gantry designs that feature two moveable primary supports, the gantry is supported on temporary supports only long enough to advance the two primary supports along the completed deck. Once the primary supports are repositioned and reengaged, the gantry rolls over trolleys fixed to those supports. Chapter 4.0 -Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 24 of39

)

Figure 4.26 ·Erection Gantry Launched Forward, Otay River Bridge Once the decision has been made to use an overhead gantry based on the constraints of the project, the type of gantry must be chosen. The total contract bid price, the availability of existing gantries. and the potential future use of the gantry on other projects are all factors that influence the ultimate design of the gantry. Of particular importance is the length of the gantry with respect to the typical span length. The earliest gantries were designed to be slightly longer than the span length of the bridge on which they were being used. A typical gantry of this classification is shown in Figure 4.24B. The length was sufficient to span between the previous cantilever and the present cantilever being erected while supported on the rear and center supports. By minimizing the distance between

gantry support points, it resulted in a least-weight gantry design. The disadvantages to this type of gantry, however, involve the position of the rear support on the previous cantilever during typical segment erection and the increased complexity of pier segment placement and girder launching operations. Figure 4.24B shows the gantry in position during typical segment erection. The proximity of the rear gantry support to the tip of the cantilever may result in a worst case scenario for the loads on the cantilever or the pier. This would require additional temporary post-tensioning for moment or shear consideration in the cantilever or bending reinforcement in the pier above the service level requirements. During launching operations, this type of gantry requires an intermediate step to position the temporary nose support over the pier to begin pier segment placement operations. Alternately, a temporary pier bent may be required to support the nose where a span is exceptionally greater in length than the typical span.

The evolution of launching gantries has recently been towards girders whose total lengths are equal or slightly greater than twice the typical span length (Figure 4.24A). This has been made possible largely due to the more efficient use of materials than the first-generation gantries, and due to a recognition that additional bridge reinforcing and associated labor is more expensive over the course of a large project than additional gantry length. As is demonstrated in the schematics in Figure 4.24A, the longer girders offer the advantage of ensuring that loads transmitted to the

)

superstructure remain over the piers or at ]east in the very near vicinity. Pier segment p1acement and girder advancement operations are simplified by allowing the simultaneous placement of the typical segments of a cantilever and the pier segment at the following cantilever pier location.


Page 25 of39

As a practical matter, the tendency is to size a gantry based on twice the "typical" span length. This keeps the gantry to a reasonable length to facilitate erection and launching operations for the majority of spans. For span lengths in excess of the typical span, special, though not necessarily complex, procedures will need to be carried out to allow the gantry to be launched from one pier segment to another.

Figure 4,27- Self-Launching Dual Erection Gantry for the H-3 Windward Viaduct, Oahu, Hawaii

! Chapter 4.0 -Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 26 of39

Figure 4.28 -Launching Gantry for Hanging Lake Viaduct Glenwood Canyon, Colorado

4.4.4 Hauler In some cases. a specialized segment hauler may be used to transport segments at the erection site. This is sometimes used to deliver segments over the completed structure to the erection gantry. When this is the case. it is advantageous to match the width of the hauler to the webs of the box girder. The loaded hauler places significant concentrated loads on the bridge. and local bending of the top flange should be minimized. Care should be taken to limit the path taken by the hauler to avoid overloading the structure.

4.5 Special Topics 4.5.1 Surveying and Deflections Surveying and geometry control are equally important during segment erection as during casting. Because of the cantilever length. a small error in orientation at the beginning of the cantilever can have a significant impact at the tip. Survey personnel should be experienced in this type of construction, and maintain good coordination with the site engineering staff to keep the bridge in proper alignment. Controlling cantilever geometry during erection can be complex for a balanced cantilever bridge. This is because the bridge will deflect many times during construction, due to unbalanced segment weights, closure sequence or unbalanced erection equipment.

Surveys should be carried out on a daily basis, and should always be performed before or near sunrise to avoid tip deflections associated with differential temperatures. The survey data should be used to compare the projected position of the cantilever tip to the target position for that stage. Note that the target position may vary from day to day as the structure is loaded -it will not necessarily coincide with the final alignment.


Page 27 of39

The construction engineer plays an important role in this effort. The construction engineer should calculate the deflected shape of the cantilever at multiple phases during erection. This may include the completion of each cycle, before and after stressing PT, and before and after major shifting major equipment (such as launching an erection gantry). These deflections can be combined with the actual casting data by the site personnel, and compared against the daily surveys.

4.5.2 Pier Segments Pier segments often demand special design and construction effort. They are the critical transition element from the super to the sub-structure, and as such can be relatively complex and congested. They are often the heaviest segments on the project. There are three main types of pier segments

in general use. 4.5.2.1 Cast in Place. In this case, the entire segment is cast as part of the substructure. The great advantage of this method is in weight. Since the segments with a thickened diaphragm can be the heaviest of the project, using a cast-in-place pier segment can reduce the heaviest load for transportation and erection equipment. This frees the designer to use a larger diaphragm, which is often advantageous in seismic regions with heavy column reinforcement that must be continuous into

the pier cap.

Figure 4.29 - Cast In Place Pier Segment, Otay River Bridge These advantages do not come without costs. Chief among them is the impact to the erection schedule. When the pier segment is cast-in-place, there is no match-castjoint with the first precast segment. Therefore, a small CIP closure is necessary between the two. This requires the first precast segment to be supported in its proper position while the closure pour is formed, poured and cured. This operation can take several days, where a match-cast segment cyc1e takes only a few hours.

J Chapter 4.0- Construction of Precast Segmental Typical Balanced Cantilever Bridges

Page 28 of39

Figure 4.30- First Precast Segment Supported Prior to Casting Closure ]oint, Otay River Bridge.

Furthermore, for a cast in place pier table, all of the rebar is tied and the concrete is poured in place. The reinforcement is often tightly congested. All of this work is performed away from the controlled conditions of the casting yard, and often at significant heights. Geometry control is another important consideration for a CIP pier table. Care must be taken to ensure that the pier segment is both in the correct position, and matches the cross section of the precast segments. Tendons ducts must also be in close alignment across the CIP joint. Additional space for coupling the ducts across the closure should be provided by including a small blackout on either side.

Fif(ure 4.31 - Blockout.for Ducts at Construction ]oint


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4.5.2.2 Precast Pier Segment In this case, the pier segment is part of the typical precasting operations. Precast pier segments are often not as long as typical segments, in order to reduce their weight. This and the thicker internal diaphragm often require a unique mold for the pier segment.

Figure 4.32- Placing Precast Pier Segments, PR181

There are two main advantages to precasting the pier segments. The first is that the exacting rebar placement and concrete operations take place in the casting yard, where the conditions are much more controlled. The second is in segment placement during erection. The need to have a CIP joint between the pier and first typical segment is eliminated, greatly enhancing the erection speed of a typical cantilever. In most cases, a precast pier segment is supported on bearings. This means that structure stability is an important consideration during construction. The large unbalanced loads that are a necessary part of balanced cantilever erection can be difficult to accommodate with a bearing connection in the absence of a gantry designed to provide stability. Supplemental towers, tie-downs, brackets, or combination are needed to provide global stability, as shown in Figure 4.33. The cost of these stability structures can become substantial as the unbalanced loads increase.


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BJ SING!£ TENSION AND COMI'RESS/ON f'ROI'

AJCOWUN FRAME SUPPORTED

I

I

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!

X

I I

X X

i i I

V'-'"'P{»rl Frame I

CJ 00081£ COUI'RESSION f'ROPS

Tomp Foollrg DHJJXIWAHY TENSION TIES

Figure 4.33 -Methods for Additional Stability

4.5.2.3 Precast Shell This is a hybrid of the CIP and precast pier segments. In this method, the exterior shell of the pier segment is precast in the casting yard. It is then transported to the site, and positioned over the continuous rebar coming up from the colunm. Supplemental rebar is then tied in place, and the internal diaphragm is cast, using the concrete shell as a portion of the formwork.

Figure 4.34- Precast Shell Installation


Page31 of39

This method brings with it both the advantages and drawbacks of conventional methods. The chief advantage is the ability to create a monolithic connection with the pier, while still maintaining a match-cast joint at the pier segment. This provides the global stability of a CIP pier table, without sacrificing the speed of segment erection. However, many of the challenges of CIP work remain. It is necessary to have continuous rebar between the precast shell and the CIP diaphragm. This often means a large number of rebar couplers on the interior face of the shell. Complex rebar and higher-strength concrete must be placed on site. An additional consideration is the degree of grade and crossfall. The precast shells must be supported accurately in order to set the alignment correctly for the entire cantilever. Placing the segment and tying the supplemental rebar can be a challenge when the segment is at a steep angle to the vertical column steel. In situations where these challenges can be met, the precast shell method can offer an advantage in erection speed.

Figure 4.35 -Installation of Precast Shel~ Vancouver Millennium Line


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Figure 4.36- Installation of Supplemental Rebar Inside Precast Shell, Dallas High-S

4.5.3 Expansion Joints For longer viaducts, it can be necessary to introduce expansion joints to alleviate the effects of creep, shrinkage and temperature. For span-by-span precast segmental construction, expansion joints are normally located at the piers. However, for balanced cantilever construction, there are three different possibilities. Each method places the joint at a different location within the span. The first is the quarter-span hinge. In this case, the hinge is located at the quarter point of the completed span, or halfway out one of the cantilevers. The hinge is a concrete seat type hinge, as is common for many viaducts cast in place on falsework. The challenge in this case is making this configuration compatible with balanced cantilever erection.

This is achieved by blocking the two halves of the hinge together during cantilever erection. The two hinge halves are effectively treated as a single segment, and temporary cantilever tendons are installed through them to erect the remainder of the cantilevered segments. Once closure has been

cast for that span, the temporary tendons holding the hinge together are severed, and the blocking removed. It should be noted that this method often requires tightly congested post-tensioning and reinforcement in the hinge segments. If this method is adopted, constructability should be an important consideration at every stage of design and construction.


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Figure 4.37- Quarter-Span Hinge Erection Sequence In its permanent configuration, this type of hinge only transfers shear across the joint, and relies on its location at an inflection point to avoid abrupt angle breaks under live loads. Important considerations for this method include the weight of the segments, which will affect the geometry of that cantilever, and the complex temporary post-tensioning operations that are necessary. A schematic of the system employed on the H3 viaduct in Hawaii is shown in Figure 4.37 above.

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Figure 4.38- Quarter-Span Hinge Installation, H3 Viaduct, Hawaii


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The second method is the mid-span hinge. In this method, the joint is located in the middle of the completed span, between two adjacent cantilevers. Continuity is created by steel beams that cross the joint, and are anchored in both sides. There are several possible configurations for the support of these beams, but they are all intended to transfer moment as well as shear, while allowing longitudinal movement. Transfer of moment is important, because without moment continuity the angle break under creep redistribution and live load would be unacceptable. The beam configuration for the Otay River Bridge is showo in Figure 4.39 below.

Figure 4.39- Mid-Span Hinge Schematic

) This method enjoys some advantages due to its compatibility with the balanced cantilever erection sequence. After an entire cantilever is erected, the beams can be lifted into position, and pushed back into the completed box girder. The adjacent cantilever is then built, and the beam is pushed back across the expansion joint and secured in its final position. This method does require special diaphragm segments, whose purpose is to anchor the steel beams to the concrete box girder. As with any diaphragm segment, weight is an important consideration. Beam installation is performed inside the concrete box girder, which can limit the space available for work. A generous allowance for construction tolerances for all of the various components (beam, segment, bearing, geometry) will help to avoid placement problems in the field. The beams serve as an important structural member, and their long term performance should be considered during design. This would include issues such as access and bearing replacement. Awareness of the maintenance requirements should persist during construction, when the long term impact of proposed modifications should be weighed against any gains to constructability.


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Figure 4.40 -Mid-Span Hinge Beam Installation, Otay River Bridge

The third method is to place the expansion joint at the columns. This can be achieved by building the spans adjacent to the expansion joint on falsework, when that option is available. However, balanced cantilever construction is often selected to avoid the need for falsework. In these cases, temporary post-tensioning can be used to erect the spans adjacent to the expansion joint in balanced cantilever. With this method, the pier segments at the expansion joints are blocked and secured together to create a monolithic pier segment. The segments on either side of the joint are equipped with ducts for temporary cantilever tendons. These spans can be built out from the expansion joint pier in typical balanced cantilever fashion, held in place by the temporary tendons. Once continuity has been achieved on both sides, the temporary tendons are cut, and the blocking removed. This method is generally applicable only for shorter spans.


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Figure 4.41- Column Expansion Joint Erection Schematic

4.5.4 Mid-Span Closure Typical balanced cantilever construction includes a small closure joint poured at mid-span, ranging from one to two feet in length. This closure is formed and cast in place, with the precast segments forming the respective bulkheads. For longer closure joints, one or two sets of the typical segment rebar may be required. The most important consideration with performing the mid-span closure is aligning and securing the opposite cantilever tips. It is likely that small adjustments in both vertical and horizontal alignment will be necessary. Even if there is no need for adjustment, the tips should be firmly held in position to avoid any relative movement during curing of the closure joint. This is generally achieved via strongback beams placed across the joints. The beams should be configured to transfer a moment to the box girder, so tension tie-downs are often necessary. The contractor should coordinate with the construction engineer to estimate the necessary strength and rigidity of the tie-down beams, and to verify that they will not damage the deck under anticipated loads. Provisions for securing the strongback beams to the deck should be developed early, so they can be easily integrated into the casting yard work.


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Figure 4.42- Strongback Beams at Closure Joint Pour

4.5.6 Temporary Access Openings As with all segmental construction, much of the work is performed on the interior of the box girder. However, moving people and equipment to the interior from the open end of the cantilever is impractical, and can be unsafe. In addition, there is a need to take the equipment out after completion of the mid-span closure. For these reasons, it is advisable to include temporary access openings at regular intervals along the bridge deck. Note that access to the interior will be convenient for the first segment (for example, for installing temporary PT bars), so some of the access locations should be located at or near the piers.

4.6

Engineering Construction engineering is an important feature of balanced cantilever construction. While construction schematics are typically included in a design, the wide variation in schedule, methods and equipment available make it unlikely that the contractor's chosen method will match the assumed conditions. Listed below are some of the tasks typically associated with construction engineering for a precast balanced cantilever bridge.

4.6.1 Built-in Loads Compared to other types of bridges, balanced cantilever bridges are more sensitive to built-in loads. Built-in loads are generally associated with a closure pour sequence. That is, loads that are present when a closure pour is cast are «locked in" to the completed structure. The sequence leading to built-in loads assumed for design should be indicated on the plans. This might include the sequence of closure pours, sequence of stressing continuity tendons, pre-loading or ballasting, or equipment loads. The construction engineer should have a good understanding of what is required in the design sequence, and identify and resolve any discrepancies in the contractor's proposed sequence.


Page 38 of39

4.6.2 Erection Loads Construction of a balanced cantilever bridge includes numerous different loading conditions, which are applied to a structure that is different after every stage. It is important that the full structure be checked at all critical phases and loading conditions. These may include the loads due to an unbalanced segment, reactions from an erection gantry, counterweights, post-tensioning, wind and miscellaneous equipment. In some jurisdictions, it is necessary to check the structure for a low-level seismic event for the governing temporary conditions. Erection with a gantry is generally the most complex in this regard. The typical segment erection and launching sequences will contain numerous steps, with the reactions placed at multiple locations. Close coordination between the truss supplier, contractor and construction engineer is necessary to identify the critical cases. Transverse eccentricity should always be considered, as the induced torsion can be significant when the gantry negotiates tight curves. In addition, it is often necessary to check the structure for segment delivery cases. When the completed portion of the deck is used to transport and stage the segments, large local loads can develop. The AASIITO Specifications provide guidelines for construction loads and load combinations, some of which are specific to balanced cantilever construction. These guidelines are often supplemented with additional loads to suit the project, such as seismic or collision loads. One load case that is defined by the Specification is the accidental release case. In this case, a dyuamic impact factor of 2.0 (twice the segment weight) is applied to approximate catching a lost segment load using lifting equipment. This is an ultimate load case, and is frequently a governing case among the construction loads.

4.6.3 Cambers and Deflections Related to the calculations of the critical erection loads are the development of camber and deflection data. Before segment casting can begin, the construction engineer must develop the camber that is to be included in the casting coordinates. This is a function of the construction sequence, the loads and equipment used, the concrete age at erection, and the properties of the concrete. Again, close coordination between contractor and construction engineer is necessary to create an accurate estimate of these parameters. For some projects, testing of the concrete is required in order to develop accurate creep and shrinkage characteristics. In these cases, testing should begin early, as tests of concrete behavior can take six months or more.

4.6.4 Temporary Post-Tensioning Calculations are necessary to verify that the segment joints are evenly stressed during installation, when the segment self weight and construction equipment are considered. For variable depth cantilevers, this can lead to variations in temporary PT forces along the length, as the segments become lighter towards the end of the cantilever. It is important to maintain compression on the epoxy joint throughout its cure time, since stress reversal during this period can destroy the bonding capacity of the epoxy. It is also important to maintain compression on the bottom flange after the cantilever tendons have been stressed, as the weight of the segment is often insufficient to keep the joints near the tip closed. This can lead to cracks in the cured epoxy, or to gaps and geometry errors in uncured epoxy.


Page 39 of39

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TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 5.0 CONSTRUCTION OF CAST-IN-PLACE BALANCED CANTILEVER BRIDGES

5.0

Construction of Cast-in-Place Balanced Cantilever Bridges

3

5.1

Introduction

3

5.2

Construction Methods

6

)

Chapter 5.0- Construction of Cast-in-Place Balanced Cantilever Bridges

Page I of28

TABLE OF FIGURES

)

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 5.0 CONSTRUCTION OF CAST-IN-PLACE BALANCED CANTILEVER BRIDGES Figure 5.1

Cantilevering Construction Method

3

Figure 5.2

Balanced Cantilever Construction Method

3

Figure 5.3

Lahn Bridge

Figure 5.4

Cast-in-Place Balanced Cantilever Bridge Design and Construction: Typical Cast-in-Place Balanced Cantilever Bridges

5

Figure 5.5

Pier Table Construction, Wakota Bridge, Minnesota

6

Figure 5.6

Pier Table Construction, Wakota Bridge, Minnesota

7

Figure 5.7

Strong Back Across a Closure Pour

7

Figure 5.8

Concept of Cantilever Post-Tensioning in Cast-In-Place Segmental

4

Construction and Concept of Continuity Post-Tensioning in Cast-In-Place Segmental Construction

9

Figure 5.9

Cast-in-Place Balanced Cantilever Bridge Design and Construction: Construction Out of Balance Loads

11

Figure 5.10

Temporary Supports During Construction, Puyallup River Bridge, Washington

11

Double-Walled Pier Superstructure Connection, Lower Screwtail Bridge, Arizona

12

Figure 5.12

Monolithic Column Superstructure Connection, Tsable River Bridge, Vancouver, BC

12

Figure 5.13

Cast-in-Place Balanced Cantilever Bridge Design and Construction: Un-symmetrical Pier Table

14

Figure 5.14

Cantilever Erection Sequence, Wakota Bridge, Minnesota

14

Figure 5.15

Deck Reinforcement and Tendon Ducts, Wakota Bridge, Minnesota

15

Figure 5.16

Cast-in-Place Balanced Cantilever Bridge Design and Construction: Special Form Traveler

15

Figure 5.11

Figure 5.17

Top View of 1-895 Form Travelers on Pier Table

16

Figure 5.18

1-895 Form Traveler & Pier Table

16

Figure 5.19

1-895 Form Traveler

17

Figure 5.20

1-895 Form Traveler Side Photo

17

Figure 5.21

1-895 Traveler Just Prior to Mid-span Closure

18

Figure 5.22

End view of Traveler looking from the leading end of construction

20

Figure 5.23

Elevation of Form Traveler Detailing Major Components

21

Figure 5.24

The launching rams [G2] have pushed the traveler forward to the leading edge of construction. The front bogey assembly [G4] is on the main rails

Figure 5.25

22

Rear tie-down system for one main frame [G3], rear bogy assembly [H1], rear tie-down bars, and pull-down ram [H2]

23

Figure 5.26

End view of Form Traveler

25

Figure 5.27

Repetitive Casting Cycle

26

Figure 5.28

Sequence of Concrete Placement

27

Figure 5.29

Abutment Segment

28 /


Page 2 of28

I

5.0 5.1

Construction of Cast-In-Place Balanced Cantilever Bridges Introduction Free cantilevering is a method of construction to build outward from a fixed poiot to form a cantilever structure, without temporary support, using staged construction as shown in Figure 5.1. Definition of "cantilever" from Webster's Dictionary is: "A rigid structural member projecting from a vertical support, especially one io which the projection is great in relation to the depth, so that the upper part is in tension and the lower part in compression". Another meaning of "cantilever" is "bracket".

Fll(EQ POINT

Figure 5.1 - Cantilevering Construction Method

When two opposing free cantilever structures are attached as a single structure and erected at the same step, it is termed "balanced cantilever construction method" as shown in Figure 5.2.

,r- FORM TRAVEI,ER

1-----"---l_

FORM TRAVElER

--'---_-.....,._'r-_--'-_

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Figure 5.2- Balanced Cantilever Construction Method

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Page 3 of28

In basic terms, cast-in-place (c.i.p) construction denotes a construction process where the segments are progressively cast on site at their final position in the structure. In comparison precast construction the

segments are prefabricated at a casting plant, either on site or at a remote facility, transported to the project site and erected as a completed unit in the final position. With cast-in-place construction the bridge segments are built in place, in progressive increments; one

segment at a time. The manufacturing switches from a controlled enviromnent (a casting yard) to the superstrocture itself. The segment forms cantilever from the previously cast segment and remain in place until the new concrete segment has achieved sufficient strength so that it can be post-tensioned and permanently held in place to the previous segments cast behind it.

The application to cast-in-place reinforced concrete bridges took place for the first time with the constroction of a 68 meter span bridge across the Rio de Peixe in Brazil in 1930. However, the cantilevering method for reinforced concrete never gained popularity due to excessive deflection and

heavy reinforcing. Dr. Ulrich Finsterwalder of the firm Dyckerhoff & Widmann AG (DSI International) successfully applied post-tensioning to a cast-in-place concrete bridge using the balanced cantilever method with constroction of the Lalm Bridge at Balduinstein in Germany in 1950-1951, after World War II (see Figure 5.3). The bridge is fixed at both ends and has a span length of203.65 feet (62.09m). This bridge is considered the pioneer of modern long span segmental concrete bridge constroction.

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Figure 5.3 - Lahn Bridge (Drawing Courtesy ofDywidag Systems International, Inc.) After successful completion of the Lahn Bridge, the system was improved over the years and gained popularity for constroction oflong span bridges across the world (see Figure 5.4). Castin-place balanced cantilever bridges are especially suitable for construction or long spans over

deep valleys and rivers where placing temporary supports is not possible of cost prohibitive. The only drawback of the system is the time required for superstructure construction. While the time required

for constroction of a typical segment (usually about 5 days, however this can vary considerably depending on the learning curve) is much longer than precast segmental construction, this should be considered in the context of the longer span lengths for which cast-in-place balanced cantilever construction is used. The span length for cast-in-place segmental bridges is a function of several

different factors; the economical range is about 70 to 250m (230 to 820ft) with major cost factors being the large pier tables and the specialized equipment required to construct the segments. At the beginning of superstructure construction, there is a learning curve for the construction crew which results in a much slower pace of construction. The learning curve effect may be particularly apparent during construction of the first pier table. Sufficient consideration should be incorporated in the

project schedule for the learning curve of the first pier table and initial segment casting cycle.


Page 4 of28

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Figure 5.4- Cast-in-Place Balanced Cantilever Bridge Design and Construction: Typical Cast-in-Place Balanced Cantilever Bridges

) Chapter 5.0- Construction of Cast-in-Place Balanced Cantilever Bridges

Page 5 of28

5.2

Construction Methods In cast-in-place balanced cantilever construction, a starter segment is first constructed over a pier

colwnn as shown in Figure 5.5 and Figure 5.6. The starter segment over the pier is called a piertable. From this starting point, the bridge can be built from a single pier or multiple piers at the same time using form-travelers moving toward mid-span. At mid-span, the two adjacent cantilever tips are connected to make a continuous structure with a closure pour segment. Typically a formtraveler or steel strong backs are attached to both cantilever tips to prevent differential movement during the closure pour. These attachments can also correct any horizontal misalignment as well as elevation ofboth tips (see Figure 5.7).

Figure 5.5- Pier Table Construction, Wakota Bridge, Minnesota (Photos and graphics courtesy ofParsons)

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Chapter 5.0 ~Construction of Cast-in-Place Balanced Cantilever Bridges

Page 6 of28

)

)

)

Figure 5.6 ~Pier Table Construction, Wakota Bridge, Minnesota (Photos courtesy of Parsons)

Figure 5. 7- Strong Back Across a Closure Pour (Photo courtesy of Parsons Brinckerhofl)


Page 7 of28

In classical cantilever bridge construction, segments are placed symmetrically from the pier table with typical segment lengths ranging from 10'-0" to 16'-0". Segment lengths longer than 16'-0" are rarely used due to longer segments producing large out ofbalance loads during construction. In addition, 16'0" segment form-travelers are widely available on the market, and can often be reused without ordering a new one. In special cases, cantilevering with form-travelers longer than 16'-0" has been accomplished. The cantilevering process is not possible without the use of a specialized piece of equipment; a form traveler. The form travelers are a self-launching structural system that is supported off the leading cantilever tip and is used to support the segment formwork and weight of the newly cast segment. The form traveler remains in place until the new segment has gained sufficient strength to be posttensioned to the previous cantilever segments where the segment will remain in its final structural position. Provisions are made that allow the form traveler to move forward, at an increment of one segment length at a time, as the cantilever is constructed. A detailed discussion of form travelers is provided in this chapter The balanced cantilever method of construction is the most common technique for cast-in-place segmental bridges. Several advantages have contributed to the success of the balanced cantilever method. One of the most important advantages is the repetitive cycle that is used to construct each segment, which leads to efficient and rapid construction of the superstructure. This method is very feasible for long span bridges which are located high above the ground, eliminating the use of extensive falsework. Access from the ground is only necessary for construction of the abutments and piers. Several creative and cost saving methods for constructing the superstructure are available when terrain under the structure is inaccessible or particularly difficult to build from. Long span balanced cantilever bridges require post-tensioning for support during construction and under service loading after the structure is completed. During construction the cantilever am1 increases in length with the casting of each additional segment and large tension stresses are applied to the top deck of the segment. The stresses are smallest at the cantilever tip and increase to a maximum adjacent to the pier. A series of post-tensioning tendons, called cantilever tendons, are located in the

top deck to resist the tension and keep the cantilever tip from sagging. These tendons tie back a newly cast segment to the existing structure and must be stressed from the leading cantilever tip each time a new segment is cast. This concept is best illustrated with the diagram provided in Figure 5.8. The majority of tendons are located at the point of maximum stress and decrease at the end of a completed cantilever ann. Each cantilever tendon passes through a thin metal conduit, referred to as a duct, that stretches from one end of the cantilever tip to the other; each tendon is located in a separate duct. The cantilever tendons increase in length with the addition of new segments and reach their maximum with a completed cantilever.

When two adjacent cantilever arms are connected with a closure segment a span is complete and continuity is provided from pier to pier. After continuity is achieved a redistribution of stresses takes place reducing the values applied during construction. The span must withstand the self-weight of the structure combined with design loads such as vehicles, temperature, future overlays and snow. Large tension stresses are now applied to the bottom deck of the cross-section. The stresses are smallest adjacent to the pier and increase to a maximum at mid-span. Continuity tendons are located in the bottom slab to balance the tension stresses. Higher concentrations of continuity tendons are required at the location of maximum tensile stress and decrease towards the piers. Continuity tendons are stressed at concrete anchor blocks inside the box segment after the closure pour is made. Figure 5.8A illustrates this principle.

Chapter 5.0- Construction of Cast-in-Place Balanced Caotilever Bridges

Page 8 of28

Bottom slab of closure

A pair of continuity tendons is anchored at a concrete block cast

Figure 5.8 Concept of Cantilever Post-Tensioning in Cast-In-Place Segmental Construction A pair of cantilever tendons ties back a new segment to the

existing structure

Maximum number of tendons is at the point of maximum stress

L

The cantilever tendons increase in length with

the addition of new segments

Figure 5.8 Concept of Continuity Post-Tensioning in Cast-In-Place Segmental Construction


Page 9 of28

Major construction loads considered in cantilever construction are as follows (see Figure 5.9): •

Segment dead loads, including fresh concrete

•

Form-travelers

•

Construction equipment

•

Construction materials

•

Construction live loads •

Windloads

•

Seismic loads

•

Accidental loads, such as loss of one form-traveler

For horizontally curved superstructures, out of balance loads also occur in the transverse direction. For this reason, a three-dimensional structural model is required for horizontally curved structures. Columns, footings, and foundations are critical elements of the cantilever structure to be checked and designed for construction loads. In addition to serviceability and strength, the stability of the overall structure must be checked. Due to large out of balance loads, it is common practice to provide temporary supports to resist out of balanced forces. Temporary supports provide the required structural stability during construction as shown in Figure 5.10. Stability during construction may also be provided by double-walled piers as shown in Figure 5.11, or by a monolithic connection between the pier and superstructure as shown in Figure 5.12.

\,


Page 10 of28

II#/

Figure 5.9- Cast-in-Place Balanced Cantilever Bridge Design and Construction: Construction Out ofBalance Loads

Figure 5.10- Temporary Supports During Construction, Puyallup River Bridge, Washington


Page II of28

Figure 5.11- Double-Walled Pier Superstructure Connection, Lower Screwtail Bridge, Arizona

Figure 5.12 -Jl1onolithic Column Superstructure Connection, Tsable River Bridge, Vancouver, BC


Page 12 of28

)

Construction Sequence Segment dead load is a large source of out of balance moment during construction of the substructure. These loads can be reduced using an asymmetrical pier-table as shown in Figure 5.13. The same result may be obtained by using a symmetrical pier table and construction of one-half segment on one side of the pier table as shown in Figure 5.5 and 5.14. The difference in cantilever length is about half of one typical segment length. In turn. full segment lengths will be constructed on each side of the pier table, producing out-of-balance loads at each stage of about half the segment. In addition, the out-of-balance load due to the form-traveler is also reduced, due to a shorter lever arm.

Once the pier table has been placed, cured and formwork removed the assembly of the first traveler can take place on top of the pier table. It typically takes approximately 2 weeks to assemble the first traveler for one end of the cantilever and another 2 weeks to assemble and attach all of the associated soffit, side and ceiling forms with hardware to the traveler prior to beginoing the initial casting cycle. The casting of the initial segment takes another 2 to 3 weeks (depending on the amount of reinforcing steel and posttensioning to be installed). Once the first segment has been cast and the traveler is advanced out on the cantilever at this point in time this will provide sufficient room on top of the pier table to allow the assembly of the second traveler on the opposite end of the cantilever. Again, the similar time of2 weeks must be allowed to assemble the second traveler and another 2 weeks to attach all of the associated forms and hardware prior to the beginoing of the casting cycle. Typically one working cycle can be accomplished in one week after the learning curve has passed. It is noted that the cycle can vary and is dependent on many variables. ) .. Pier tables are normally constructed in three to four months. One advantage to this type of construction is the repetition of activities over and over until the bridge is completed. Over the course of these cycles, the contractor has the opportunity to correct and improve procedures. The minimum pier table length is approximately 32 feet. However, NRS ofNorway has designed a special form-traveler which can accommodate a minimum length pier-table of 10'-0" as shown in Figure 5.16. The weight of a typical form-traveler including formwork ranges from 160 to 180 kips for a single cell box, and can reach 280 kips for wider twin cell boxes. The single cell box consists of two traveler frames while a two-cell box has three frames . .Form travelers are usually obtained from subcontractors, and are provided with a detailed checklist of the steps involved in operation of the form traveler. This checklist must be consistently observed during the construction process.

Form traveler installation and operation on the 1-895 Bridge over the James River in Virginia is illustrated in Figure 5.17 through 5.21. The main span length is 672 feet.


Page 13 of28

Figure 5.13- Cast-in-Place Balanced Cantilever Bridge Design and Construction: Un-symmetrical Pier Table

Figure 5.14- Cantilever Erection Sequence, Wakota Bridge, Minnesota (Photos and graphics courtesy ofParsons)


·)'

Page 14 of 28

Figure 5.15- Deck Reinforcement and Tendon Ducts, Wakota Bridge, Minnesota (photo courtesy ofParsons)

j

~

I

lC'..V(M\1:1) (3m MIN}

I

P!iASE_1

{CO_NS_T/WCl'fMWlE!lSj

PHASE3 (SPunllltl OF TIIAVELERS)

PHASE4 (READY FOR NORWJ. PROCEot/RE)

Figure 5.16- Cast-in-Place Balanced Cantilever Bridge Design and Construction: Special Form Traveler

)


Page 15 of28

···~

Figure 5.17- Top View ofl-895 Form Travelers on Pier Table (Photo courtesy ofCondotte America, Inc.)

Figure 5.18-1-895 Form Traveler & Pier Table (Photo eourte.\y ofCondotte America, Inc.)


Page 16 of28

Figure 5.19-1-895 Form Traveler (Photo courtesy ofCondotte America, Inc.)

Figure 5.20 -1895 Traveler just prior to Mid-Span Closure (Photo courtesy ofCondotte America, Inc.)

Chapter 5.0 --Construction of Cast-in-Place Balanced Cantilever Bridges

Page 17of28

Figure 5.21 -1-895 Traveler Just Prior to Mid-span Closure (Photo courtesy of Condotte America, Inc.)


Page 18 of28

Form Traveler Operation Form travelers are a specialized piece of construction equipment limited to balanced cantilever bridge construction. Most projects in the United States have been completed with two types of travelers: Hosveis travelers originally built in Norway and Dywidag travelers. They consist of two main structural frames, often referred to as horses. The front and rear trusses connect the two main frames and provide overall stability. An end view of the form traveler facing the leading end of construction is provided in Figure 5.22. An elevation of the form traveler detailing the major components is provided in Figure5.23, which will assist in the explanation and operation of the system.

Vertical Suspension System The vertical suspension system is the structural system for supporting the leading end of the bottom platform, interior soffit formwork, overhang, and wall formwork. Vertical channel hangers are suspended from the front truss connected to a series of horizontal spreader beams. The function of the spreader beams is to distribute the applied loads equally to the front truss. The front truss is supported in turn by the main frames held securely to the existing concrete segment. Each one of the formwork components is suspended from high strength bars connected to the spreader beams on top and to a secondary structural support on bottom. The purpose and operation of each component will be briefly explained.


Page 19 of28

~

~ ,...,

~

.~ --

------

!"~:-.:.: \

I

\

~

'

'

~\

\

\ \ '

''

:'

~

! !

[g Traveler Components ~- Primary structural system 1. front truss ~main frame or rails not shown in this view

B. Vertical suspension system 1. spreader beam ll. hanger channel pinned to front truss

E. Bottom platform 4. front suspension bars ~bottom platform framework and side work platform 6. exterior wall formwork

D. Interior formwork assembly $. front suspension bars B. interior framework J. interior wall formwork 3. top deck crown formwork H. Cantilever form work assembly 4. front suspension bars ~-

6. F..

supporting framework overhang formwork and work platform

Work platforms 1. upper work platform

Figure 5.22- End view of traveler looking from the leading end of construction

Bottom Platform

Bottom platform carries the concrete weight for the bottom slab and walls, and provides a safe staging area to work from. The bottom platform is held in place on the trailing end to the previous segment with a set of 4 high strength bars that pass through sleeves in the bottom slab. The leading edge is supported with 4 bars suspended from the inside spreader beams. It is noted that when the bottom platform is ready to be moved ahead the trailing end must be released from the existing segment or else it would be restrained from moving. A secondary set of bars, one each side, are suspended from the rear truss and connected to the bottom platform allowing it to move freely during launching to the next position.


Page 20 of28

l~ ::! ~

__________________________ ------------------ ::::{., ,,,, '

! ! ! ------::::::::::::::::::::::::J' Next segment to be cast

Traveler Components A. Primary structural system I. front truss 2. main frame 3. rear truss

B. Vertical suspension system I. spreader beam 2. hanger channel pinned to front truss C. Bottom platform 1. front suspension bars 2. bottom platform framework 3. rear tie-down tbrough concrete D. Interior formwork assembly 1. interior framework rail and roller system 2. rear tie-down bars through concrete

F.

Workplatforms I. upper work platform witb post-tensioning jack in place 2. lower work platform 3. rear trailing platform

G. Launching system 1. main rails and rear tie-down bars 2. hydraulic launching cylinders 3. rear bogey assembly 4. front bogey H. Tie-down system 1. rear tie-down bars through concrete slab 2. pull-down ram to release tie-down bars

Figure 5.23: Elevation ofForm Traveler Detailing Major Components Interior Formwork Assembly

Interior formwork assembly supports the concrete load between the web walls. Two high strength bars are suspended from a set of spreader beams. These bars are connected to a framework running longitudinally inside the box segment. The rear end of the frame is tied down to the previous segment with 2 bars similar to the bottom platform. The interior beams are a two-part system: they provide vertical support for the crown form and provide a rail for the interior wall support. The interior walls are supported on a frame suspended on rollers that slide independently along the interior beams. When the form traveler is launched to the next position it is necessary to leave the interior wall forms at the previous location. The web walls Chapter 5.0- Construction of Cast-in-Place Balanced Cantilever Bridges

Page 21 of28

of the segment contain heavy vertical reinforcing that can only be installed from the interior of the girder, which would not be possible with the wall panels in place. When reinforcing installation is completed the interior wall panels can be advanced forward on the roller assembly. Cantilever Formwork Assembly Cantilever formwork assembly supports the cantilevered portion of the top deck outside each web wall and provides access for construction activities such as post-tensioning of the transverse tendons. Two bars on the front end of the traveler are suspended from a spreader beam and connected to the front end of a frame running longitudinally under the overhang. The cantilever assembly includes a system for supporting the exterior web wall form. The trailing end of the assembly is supported at two locations. It is tied down to the previous segment and is suspended from the rear truss with a high strength bar.

Launching System The complete traveler assembly is supported on a pair of rails located directly above the girder web walls for direct load transfer into the superstructure. The rails provide a smooth surface to roll the traveler forward removing any irregularities of the concrete deck. Launching the form traveler system forward is a two step process: first the rails are 'pulled' forward 5.0m to the next segment position stopping just short of the leading edge at the cantilever tip, next the complete assembly is 'pushed' forward 5.0m over the rails. Details of the launching components are provided in Figure 5.24. The system is moved forward in 900mm increments with a set of hydraulic cylinders pinned between the main frame of the traveler and rails. The traveler and rails are launched with the same set of cylinders. The length of the launching cylinders limits the distance traveled with each increment.

I

Figure 5.24: The launching rams [G2] have pushed the forward to the leadin!g edge of construction. The front bogy assembly [G4] is on the main rails During launching, the traveler is top heavy and must be restrained from tipping over the leading edge. A rear bogey assembly includes rollers that grip under the flanges of the rails to restrain the rear end from tipping as detailed in Figure 24. The trailing ends of the rails must be tied down to the existing segment with high strength bars. Sleeves are cast through the top slab of the segment to accommodate these bars. The leading edge of the traveler is supported on the front bogey assembly, incorporating a Hillman roller. When the form traveler is launched to the next segment position all components move simultaneously.


Page 22 of28

Tie-Down System When the traveler is advanced to the next segment position, 5.0m away, it must be restrained from tipping over. The rear tie-down system is the main structural support that will restrain any tipping forces during concrete placement. Details of this system are provided in Figure 5.25. The rear tie-down assembly is restrained with 4 high strength bars, one set for each main frame. The tie-down bars are preloaded to a specified force to prevent the traveler from moving during concrete placement. The front end of the traveler must be lifted off the rails so it will not roll forward. Located at the front edge of the cantilever tip and below the front bogey is the front leveling ram. This rani lifts the front rollers off the rails and supports the traveler weight during concrete placement. With the traveler secured, adjustments are made to set the segment formwork to the correct elevation. Elevations are calculated with the geometry control manual by determining the segment number and construction step at that particular phase in construction. The project surveyor under strict tolerances surveys the new position. Adjusting the length of the front suspension bars changes the leading formwork position. Center hole jacks are used to make large adjustments and turning the appropriate nut with a wrench can set final elevation. Additional task-specific operations are required to complete casting cycles that are not directly related to operation of the form traveler; these activities are discussed later in this report.

Figure 5. 25 - Rear tie-down system for one main frame [G3] rear bogey assembly, [HI] rear tiedown bars, and pull-down ram [H2]

)


Page 23 of28

The following steps summarize the launching process; (the numbered components are referenced in Figures 5. 22 and 5.23):

I.

Launch the main rails to next 5.0m segment position, flush with tip of cantilever [Gl]

2.

Tie down rear end of rails with high strength bars [Gl]

3.

Lower front leveling ram so that front bogey rollers are in contact with rails [G4]

4.

Release all rear ties of the bottom platform and top deck form support [C3, D2]

5.

Actuate rear pull-down ram to engage safety clamp and release 8 tiedown bars [HZ]

6.

Release pull-down ram to transfer tipping load to rear bogeys [G3]

7.

Launch traveler forward, install and pre-load 8 tiedown bars at next segment position [HI]

8.

Install and stress rear ties of bottom platform, overhang and iop· deck form [C3, D2]

9.

Interior form system is left behind and rolled forward later to facilitate reinforcing installation [Dl]

Work Platforms An upper wmk platform is suspended from the front truss by a series of high strength bars and a lower work platform is supported from a fixed channel support to the bottom platform. The work platforms provide access for construction of segment bulkheads, post-tensioning from the leading edge and access to the traveler components. Figure 5.26 provides an end view of the traveler.


Page 24 of28

-·~ I

Figure 5. 26: End View ofForm Traveler

Segment Casting Cycle The casting cycle for a typical cantilever segment is described in the following paragraphs. Figure 5.27 provides a schematic representation of the casting cycle based on the principles discussed previously.


Page 25 of28

Day 5: Survey fmal

Overnight: Cure

elevations. Cast new segment with

concrete to achieve

crane and bucket using chutes from upper work platform.

sufficient strength

Day I: Stress transverse tendons in top slab. Stress cantilever tendons.

Day I: Release formwork and traveler tie-down

s. Launch main

~lo •~ no•• n~o;,;~n Day4: Install longitudinal tendon ducts and tendons. Install

Day 4: Advance interior formwork, install wall ties and rebar in top slab

Day 3: Install bulkhead. Install rebar in bottom slab and web walls.

Day2: Advance and anchor form traveler to existing concrete at next

segment position. Survey new segment elevations.

Figure 5.27- Repetitive Casting Cycle A casting cycle begins after placing concrete for a new segment. The first step in a new cycle is to stress the transverse post-tensioning tendons located in the top slab. It was specified in the contract documents

that the transverse tendons must be stressed prior to stripping the traveler formwork. The traveler formwork must be stripped before the traveler assembly can be launched forward. As a result, the first step can not begin until the new segment concrete has reached sufficient strength so it will not crack under the large compressive force from post-tensioning.

)

The curing of concrete thus becomes a time sensitive activity that has the potential to delay the critical path of the project. High early strength concrete is typically used to avoid a potential delay. Since it is critical that the proper concrete strength has been achieved prior to post-tensioning and launching the traveler test cylinders were used to verify the in-place strength. Day I of the casting cycle begins with the post-tensioning crew (4 members) stressing the transverse tendons while the form traveler crew (4 members) simultaneously releases the formwork and traveler tiedown bars preparing to advance to the next segment. The cantilever tendons are stressed at this time if they terminate at this location. Day 2 the traveler crew (4 of 8 members, crew is divided between the each traveler) advances the form traveler to the next segment position, trim the exterior wall form to the new height and align the formwork to the correct elevation with the assistance of the project surveyor. A carpenter installs the prefabricated bulkheads on the segment face. Day 3 the reinforcing crew (5 members) begins installation of the bottom slab and web walls of the box girder. All reinforcing steel for the segments is tied in place as the form traveler bracing and framework did not provide enough space to lift a preassembled cage into place. Day 4 when the reinforcing installation is completed on the bottom slab and walls, the crew begins installation on the top deck. In addition, the longitudinal and transverse post-tensioning ducts and tendon strands are installed, but left unstressed. Coordination of the different crews is essential in the confined area of the segment. The interior walls are rolled out, cut to the correct dimensions and form ties are

installed. Day 5 consists of final preparations for casting of the segment and placement of the concrete. The day begins early: the project engineer determines the final elevation of the new segment with any required corrections. The project surveyor must then check the final position within an hour of sunrise to eliminate any false readings caused by thermal movement of the cantilever. Concrete is typically placed in the following sequence: outside comer of the bottom slab and web wall, bottom slab, web walls and top deck Chapter 5.0- Construction of Cast-in-Place Balanced Cantilever Bridges

Page 26 of28

\_)

as illustrated in Figure 5.28. The concrete is consolidated with internal concrete vibrators. Field personnel must exercise careful quality control when placing the concrete. The first placement at the outside corner must be delivered with a low slump to 'plug' the bottom of the open wall form from the added pressure of placing the web walls above. Subsequent concrete placed must have a high slump to be placed in the congested areas of reinforcing steel and post-tensioning ducts.

Figure 5.28- Sequence of Concrete Placement

)


Page 27 of28

Abutment Segments Situated at each end of the bridge is an Abutment Segment. Abutment segments make the fmal connection between a completed cantilever and the abutment substructure. The segment depth at this point in the structure is typically constant. The abutment segments usually contain massive thick diaphragms situated over the bridge bearings to transfer the vertical load of the end span and provide anchorage for the continuity tendons. This area of the abutment segment usually contains a high concentration of reinforcing steel take require significant time to construct. Abutment segments are typically constructed in three separate lifts: bottom slab, web walls and diaphragm, top slab and deck overhang supported on shoring. Abutment segments are supported on steel falsework that remains in place until a closure segment is cast connecting to the end cantilever. Figure 5.29 shows an abutment segment under construction with the falsework in place.

Figure 5.29- Abutment Segment


Page 28 of28

TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-sUPPORTED BRIDGES CHAPTER 6.0 INCREMENTAL LAUNCHING SEGMENTAL BRIDGES

6.0


3

6.1

Introduction

3

6.2

Advantages of Incremental Launching Segmental Bridges

4

6.3

Characteristics of Incremental Launching Segmental Bridges

6

6.4

Typical Construction Sequence

12

6.5

Launching System and Equipment

13

6.6

Summary

18

6.7

Reference

18

)

Chapter 6.0- Incremental Launching of Segmental Bridges

Page I ofl8

TABLE OF FIGURES

···~

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 6.0 INCREMENTAL LAUNCHING SEGMENTAL BRIDGES

Figure 6.1

Incremental Launching Segmental Bridge

3

Figure 6.2

Schematic view of Incremental Launching

4

Figure 6.3

Incremental Launching over a Local Road in Japan

4

Figure 6.4

Incremental Launching with Temporary Pier over Railway

6

Figure 6.5

Double-Cell Fix-Belly Cross-Section

7

Figure 6.6

Four-Cell Voided Slab

7

Figure 6.7

Incremental Launching of a Bridge with Plan Curvature

8

Figure 6.8

Bending Moment Diagram and Examples of Post-Tensioning Coordination

9

Figure 6.9

Temporary External Tendons and Permanent External Tendons

10

Figure 6.10

Transverse Shift of the First Half of a Twin-Box Section on Launch Completion

11

Figure 6.11

Incremental Launching with Balanced Cantilever and Arch Construction

11

Figure 6.12

Launching of the Superstructure on Temporary Piers before Suspension

12

Figure 6.13

Casting Yard behind an Abutment

13

Figure 6.14

Pulling Launching System

14

Figure 6.15

Center-Hole Jacks and Supporting Frame Anchored to an Abutment

14

Figure 6.16

Axial Friction Launching System

15

Figure 6.17

Launch Bearing

16

Figure 6.18

Launch Bearing and Launch Pads

16

Figure 6.19

Permanent Bearing which Serves as Launch Bearing

17

Figure 6.20

Lateral Guide at the Permanent Pier

17

Chapter 6.0 -Incremental Launching of Segmental Bridges

Page 2 of 18

)

6.0


6.1

Introduction Generally, construction of incremental launching segmental bridges consists of manufacturing of a bridge superstructure by segments in a fabrication area set up behind one of the abutments. A new segment is match-cast against the preceding segment. After the concrete is hardened and launch prestressing is installed in the newly cast segment, the whole superstructure is moved forward by the length of one segment to clear the casting cell for casting a new segment. The superstructure moves on the piers, and segment fabrication continues until the first segment reaches the abutment

at the other end. The incremental launching segmental bridges combine the advantages of cast-in-place and precast concrete bridge construction. They do not interfere with the obstacle to overpass, and the casting yard can be the smallest. These advantages are precious in urban ambit or in the case of environmentally sensitive areas. Safety of workers is at the highest level, the superstructure can be cast under stringent quality-guarantee procedures, the reinforcing cages can be prefabricated at different extents, and the casting yard can be easily sheltered for continued production with inclement weather. Construction equipment is also particularly inexpensive (a launching nose, a thrust system, and a casting cell) and can be easily reused in new projects. Another basic advantage is that the yard industrialization can be easily adapted to the dimensions of the bridge.

)

Figure 6.I -Incremental Launching Segmental Bridge (Photo courtesy of PSM Construction USA, Inc.)

The incremental launching method has been successfully used in dozens of long and short bridges in Europe, Japan, and other parts of the world, although its application is limited in the North America. The incremental launching method is generally economical for prestressed concrete bridges of medium span, ranging from I 00 feet to more than 200 feet. It is applicable to longer spans with temporary piers that halve the spans during construction. Launching from the opposite abutments is sometimes adopted in the longest bridges in order to diminish the thrust force. Launching from the opposite abutments also permits halving the construction duration by working in two casting yards, although the equipment cost doubles. Chapter 6.0- Incremental Launching of Segmental Bridges

Page 3 of 18

A schematic view of the standard arrangement for an incrementally launched bridge is shown in the Fignre 6.2.

Launching Nose

Temporary Pier

Figure 6.2 - Schematic view ofIncremental Launching

6.2

Advantages of Incremental Launching of Segmental Bridges

Most of the work associated with the incremental launching method is done in a casting yard set behind one of the abutments. Because the superstructure moves forward on the piers, construction

is carried out without falsework and is not affected by the conditions under the bridge. Additional consideration is not necessary to pass over obstacles such as buildings and rivers. Because no impact at all is given to the clearances of highway or railway traffic crossing below the bridge, traffic is uninterrupted during construction.

Figure 6.3 -Incremental Launching over a Local Road in Japan {Photo courtesy ofPSM Construction USA, Inc.)


Page 4 of 18

Examples of traffic being maintained below the spans being launched are illustrated in Fignres 6.3 and 6.4. In the bridge of Figure 6.4 (launched in downtown Milan, Italy), No.340 trains passed under the bridge everyday without any speed restrictions. The electrified lines have also been kept in service. There are many advantages to incremental launching segmental bridges which include: I.

Stationary fabrication streamlines construction and saves labor. a. The casting yard, the rebar assembly yard, the stocking area, and the hatching plant (if any) are located in a small yard. This is a basic advantage in urban, congested, or environmentally sensitive areas.

b.

c.

d.

e.

f.

)

2.

Steel cages are partially prefabricated within the casting yard or in the workshop. Preassembly can be fractioned at different levels (web panels, deck slab panels, etc.) or integral. The full utilization of personnel is permitted by parallel (rather than serial) activities which are performed at short distance from one another. Site industrialization can be adapted to the bridge length and dimension. The specialized construction equipment (a launching nose and a hydraulic thrust system) can be reused on different projects if designed on modular bases. The casting cell is also generally designed with standard components. Mechanized and concentrated fabrication generally needs a crew of a constant number of workers (usually 10 to 15 people) throughout the segmental construction. Yard industrialization reduces the time required for each activity. Ahnost all materials are delivered to one place, which simplifies transportation issues. Handling of materials inside the small yard is easy and labor-saving. Generally a standard tower crane assists the casting yard for enhanced efficiency of handling. Workers do not need to be transported to several locations. Construction risks

for workers are also minimized as the casting cell is rigidly supported on the ground instead of being, e.g., suspended at the tip of a cantilever, and no activity takes place on the superstructure. g. Sheltered fabrication is uninterrupted by bad weather. Construction during winter in cold regions is possible with heat insulation if other conditions allow. Improved workmanship and quality a. The geographically concentrated fabrication makes clean and efficient management of construction and labor possible.

b.

c.

d.

The factory-like conditions and repetitive works expedite workmanship and high quality work environment. A high rate of progress can be attained by training the team with the use of mechanization. Working rhythm can be coordinated to the construction of one deck segment per week to use weekend for curing of concrete. Although the deck segments are generally as long as one-half of the span, alternative organizations with shorter segments are also possible for higher repetitiveness. The mechanized fabrication enables precise control of geometry and the concrete cover, thus further enhancing quality of construction.

The number of construction joints (weak point of any segmental structure) is minimized - two per span in general. The construction joints have through reinforcement for full ultimate cross-sectional capacity. They can be easily

bush-hammered, sand-blasted, or pressure-washed before match-casting the next segment for perfect structural continuity.

3.

Improved safety a. Little work is done at the final bridge position. Most operation is performed on b.

the ground, much simpler and safer than operation in the air. Little or no interference to the clearance of highway or railroad traffic crossing

below bridges. c.

Construction behind an abutment minimizes the impact to the third parties and surrounding environment.


Page 5 of 18

Figure 6.4 -Incremental Launching with Temporary Pier over Railway (Photo courtesy of Marco Rosignoli) Figure 6.4 shows an incremental launch over a 6-track railroad in Italy. This wide three-cell superstructure could also be cast on a general falsework; however, the complexity and cost of the falsework would be prohibitive in many industrialized countries. Launching has proven to be a cost-effective and high-quality solution in tens of difficult bridges.

6.3

Characteristics of Incremental Launching Segmental Bridges 6.3.1 Geometry Because of alternate bending moment and shear force the superstructure receives during launching, the span-to-depth ratio is usually about 17. This ratio can be increased with the use of temporary piers; this also permits savings in launch prestressing. This ratio is diminished to between 12 and

15 for high-speed railway bridges, mostly because of deflection limitations in service. Spans with equal or almost equal length (except the end ones) are preferable in order to maximize the number of equal segments. The most suitable cross-section is the single-cell box section. Double-cell box sections have also been used although construction is somewhat more complicated with respect to shuttering and

launch supports. A double-cell fish-belly section has been used in Italy for a 2700-feet-long bridge with architectural board-marked finishing of surface. Figure 6.5 shows the double-cell segment extraction from the highly industrialized casting yard. The cleanliness and order of the yard are evident in the photograph. Above the deck, the rollcompacting unit expels the bleeding water from the upper concrete layer of the deck slab to diminish the W/C ratio and increase the local strength. Three-cell and four-cell cross-sections have also been successfully launched. Figure 6.4 shows a three-cell section launched on two support aligmnents.

Chapter 6.0 ~ Incremental Launching of Segmental Bridges

Page 6 of 18

Figure 6.5- Double-Cell Fish-Belly Cross-Section (Photo courtesy of Marco Rosignoli)

Figure 6.6 shows a four-cell voided slab launched in Italy on three support alignments. This highly skewed, varying-width simply-supported span was launched onto a railroad with the help of a steel temporary pier that avoided overturning. In this case the three launching noses were inexpensive prestressed concrete blocks fixed to the front deck end with prestressing bars and braced to each other with steel angles. The central launch alignment also acted as a plan guide. Double-T beams (ribbed slabs) have been launched on short spans or onto arches. In this case the span between the spandrel colunms is generally short. In spite of their simplicity, the ribbed slabs are hard to launch due to the raised location of the cross-sectional centroid.

Figure 6.6- Four-Cell Voided Slab (Photo courtesy of Marco Rosignoli)


Page 7 ofl8

The incremental launching method is normally used for straight bridges or bridges curved with constant radius - either horizontally or vertically throughout the bridge. Bridges with variable curvature have been launched with wide launch bearings and lateral temporary piers in the most delicate cases. Launching from both abutments with central closure permits the use of two different curvatures like "S" curve. The superstructure should be of constant depth. Minor adjustment in the vertical alignment of the launch surface is attained by temporarily attaching shims to formwork. An example of incremental launching of a bridge with plan curvature is illustrated in Figures 6.7. Because of the unique character of construction, it is highly recommended that the attention should be paid at the early design phase to the possible use of the incremental launching method.

Figure 6. 7 -Incremental Launching of a Bridge with Plan Curvature (Photo courtesy ofPSM Construction USA, Inc.)

6.3.2 Post-tensioning Almost every section of the superstructure receives alternating bending moment and shear forCe from its own weight as it is launched forward. Mid-span sections which usually receive only positive bending moment also have to resist negative moment and shear force during launch.

These cyclic changes prevent use of the final tendons during launch and require launch tendons laid out centrically rather than eccentrically. There are several ways to provide launch tendons and make them coordinate with final tendons.

The principles are broadly classable to two, as described below and illustrated in Figure 6.8. 1.

Launch tendons required during launch are decided first, compensated by continuous

final tendons installed on completion oflaunch to resist the rest of dead load and live load. Launch tendons are usually laid out straight in both the top slab and bottom slab, and they provide centroidal prestress force as a whole. Continuous final tendons are provided by parabolic internal tendons in the webs or polygonal external tendons. 2.

Final tendons required against the service loads are determined first either with internal tendons or external tendons. Temporary launch tendons compensate the eccentricity of the final tendons during launch. Temporary launch tendons are removed on completion of


Page 8 of 18

launch. In some bridges, the removed tendons were repositioned and reused as part of fmal tendons. An example of launch external tendons and final external tendons is shown in Figure 6.9. Approach (I) is usually more effective as it permits progressive introduction of launch prestressing; it is also less restraining on the yard organization. The temporary launch prestressing of approach (2) needs an additional cost. The operations of tendon releasing and repositioning are expensive and time-consuming; however, the high level of launch prestressing (both permanent and antagonist tendons are present) may diminish the web thickness and increase the crosssectional efficiency.

Minimum Bending Moment

..

_-..__

!during Launch ~..

Maximum Bending Moment during Launch Design Bending Moment

)

I

--

--/

l

Final

; I

--

"" -

l

" '!'

/

Temoorarv External Launch Tendons

!

-- /T'-.,

i

Ten~ons

-

__......-u

1'

Launch Tendons

Permanent Internal Tendons

I

-- --

--

r

Permanent External Tendons

1

-- -rPermanent

~ern aI Tendons

Figure 6.8- Bending Moment Diagram and Examples ofPost-Tensioning Coordination


Page 9 of 18

Figure 6.9- Temporary External Tendons and Permanent External Tendons (Photo courtesy ofPSM Construction USA, Inc.)

6.3.3 Application of Precast Segmental Construction The incremental launching construction method has been mainly used for cast-in-place bridges as this permits combining the advantages of the industrialized and repetitive work processes with those deriving from a small number of construction joints. Nevertheless, it is suitable for precast segmental construction as well. Bridges composed of precast segments arranged along temporary support rails, connected by closure joints or epoxy coating, and incrementally launched offer several advantages which include:

Construction of most of the superstructure is independent of pier construction, as precast segments can be stored elsewhere.

Yard operations are limited to the segment arrangement along the support/launch rails, the joint sealing, and the introduction of post-tensioning in the new sections of the superstructure.

The construction duration can be half of that required for cast-in-place, although with additional labor costs and a precast yard because of these additional activities.

6.3.4 Other Applications Commonly used launch technique is to launch the superstructure from one abutment towards the opposite one. Expansion of application includes launching from the opposite abutments with midspan closure and launching followed by transverse shifting to clear the launch alignment for the construction of new bridge strips. An application of this construction method in Italy is shown in Figure 6.10. The first half (28-feet wide) of the twin-box section is being shifted rightwards on 167-feet spans- in the photograph, the box-girder is leaving the temporary piers. Launching can also be combined with other construction methods. Examples include construction

of the approaches of bridges where longer central spans are built by balanced-cantilever construction (with or without stay-cables), and construction of the superstructure of arch bridges (Figure 6.11 ).


Page 10 of 18

)

Figure 6.10- Transverse Shift of the First Half of a Twin-Box Section on Launch Completion (Photo courtesy of Marco Rosignoli) ~

~2\IV\1\1\)1

L..,l-~:1.....,11

)

Jlll

[_ _ _----,..__.,....--_ _ _]

]1

Figure 6.11 -Incremental Launching with Balanced Cantilever and Arch Construction

Cable-stayed bridges can be built by incrementally launching the continuous superstructure onto temporary piers and by permanently suspending it from a tower on launch completion. Figure 6.12 shows a cable-stayed bridge built by incremental launching in Italy. At the launch completions, the crossbeams that anchor the stay-cables are generally located above the temporary piers. Also this bridge was launched onto railways in service without any interference.


Page II ofl8

Figure 6.12- Launching of the Superstructure on Temporary Piers before Suspension (Photo courtesy of Marco Rosignoli)

6.4

Typical Construction Sequence Planning of segment construction involves defining the casting sequence, arranging the casting

yard, and pre-sizing the launch equipment. Optimum organization depends on the length of the bridge, the number and length of segments, and the construction schedule. All these parameters

)

influence the level of industrialization of a casting yard.

The casting yard is usually set behind one abutment. In the case of settlement or no embankment is available, the formwork is supported by temporary supports. If the bridge has a longitudinal gradient, it is preferable for the superstructure to be launched from the lower elevation, so that no braking equipment is necessary during launching. If the number of segments is large and enough space is available, it is convenient to create rebar cage preassembly area. The rebar cage preassembly area is usually set behind the casting cell and a gantry crane carries the rebar cage to the casting cell. Length of segments between 35 feet and I 00 feet is generally economical. It depends on the location of construction joints, typical span length, concrete volume, available space, and so on. Longer segments shorten construction period, but expands the casting cell. It is desirable for construction joints to be located at section of low

bending moment. A half of a span with construction joints at the span quarters is a common conclusion for length of segments. A representative working cycle for typical incremental launching segmental bridges with a boxsection consists of following steps:

I.

2. 3.

4. 5. 6.

7.

Set bottom slab form and side forms Place reinforcing bars and tendons in the bottom slab and the webs Cast concrete in the U-section, cure it, and remove the internal web forms Set the inside form table for the deck slab Place reinforcing bars and tendons in the top slab Cast concrete in the deck slab and cure it After the concrete has reached the strength required, open the external forms and stress the launch tendons

8. 9.

Launch the superstructure by the length of one segment Repeat the process for the next segment


Page 12 of 18

One full construction cycle typically takes about one week to ten days. One week is generally preferred to cure the deck slab concrete during weekend. In this case, a complete span is cast every two weeks. When the bridge is very long, it may be convenient to divide the production into two areas although this increases the total length of the casting yard. Therefore, a higher level of industrialization is generally preferred.

")

Accurate setting of the formwork is very important so that the sliding bottom surface is smooth and maintains the launching direction accurately. Forrnwork is of steel or plywood panels, selected depending on the number of cycles, i.e. the number of segments. The launching surfaces are generally match-cast onto neoprene-Teflon plates placed onto stiff stainless-steel extraction rails. Load deflections of the extraction rails must be minimized. Two persons are generally necessary at every pier during launching to insert low-friction plates

between the launching bearings and the superstructure. On completion of launch, temporary bearings are replaced by permanent bearings after lifting the superstructure with hydraulic jacks. Continuous final tendons, either external or internal, are installed and prestressed afterward.

Figure 6.13- Casting Yard behind an Abutment (Photo courtesy ofPSM Construction USA, Inc.)

6.5

Launching System and Equipment Some unique systems and equipment are necessary to incremental launching method.

6.5.1 Launching system There are several schemes to the system moving the superstructure forward. Among them, two

commonly used launching systems are pulling launching and friction launching. Chapter 6.0- Incremental Launching of Segmental Bridges

Page 13 of 18

(i) Pulling launching Post-tensioning strands or bars are used to tow the superstructure. Center-hole jacks are set against a support structure anchored to an abutment. The other ends of the tensioning elements are connected to the superstructure by means of steel launching pins, steel beams, or steel brackets. The steel launching pins are attached to the rear end section of the new segment. The steel launching beams or the brackets are connected to the webs or the bottom slab by means of prestressing bars or anchoring bolts. The speed of launch depends upon the types of jacks and pumps and is usually from 10 to 20 feet/h. The scheme is illustrated in Figure 6.14 and 6.15.

Figure 6.14- Pulling Launching System

)

Figure 6.15- Center-Hole Jacks and Supporting Frame Anchored to an Abutment {Photo courtesy ofPSM Construction USA. Inc)

(ii) Friction launching Another way to launch the superstructure is to use one or more pairs of launchers placed under the

webs of the cross-section. A launcher is composed of vertical jacks and horizontal pistons. After the superstructure is hoisted from bearing blocks by vertical jacks, horizontal pistons push the superstructure forward. The thrust force is transferred by friction between the vertical jacks and the concrete bottom surface. Then, the superstructure is lowered onto the bearing blocks again by

retracting the vertical jacks, and the longitudinal pistons are finally retracted to repeat this cycle. Chapter 6.0- Incremental Launching of Segmental Bridges

Page 14ofl8

In the case of two-cell cross-sections, the friction launchers can also be placed in axial position as

in the case of Figure 6.16. Compared to pulling launching system, friction launching system offers many advantages that include following: (a) Thrust force is shared by launchers. Heavy superstructure can be launched by placing synchronized launchers on every pier, which is difficult with pulling system in which thrust force is transferred at one transmission point and create stress concentration. (b) The total electric control of the hydraulic system permits synchronization of the action of launchers and speeding the launch that reaches 30feet/h. (c) Friction launchers permit downhill launching and are much safer than the pull-based systems.

) Figure 6.16- Axial Friction Launching System (Photo courtesy of Marco Rosigno/i)

6.5.2 Launch bearing and lateral guide The superstructure is supported temporarily by launch bearings before whole launching process completes. The launching bearings are made of concrete or steel, set on the top of the piers under

the webs. The top of the launching bearings are covered by polished stainless steel sheet. Launch pads are inserted between the superstructure and the launching bearings. The launch pads are made of sandwiched neoprene sheets and steel sheets. A Teflon plate is glued to the bottom surface of the pads. The pads are continuously fed until the designated launching length is reached (Figure 6.17 and 6.18). Contact of the stainless steel sheet and the Teflon plate reduces friction to 2-4%. The edges of the launching bearings are rounded so that the sliding plates can be inserted without difficulty. On completion of the whole launch, launch bearings are replaced by permanent bearings. Some types of bearings are used as launch bearing as well as permanent bearings. An

example is shown in figure 6.19.


Page 15 of 18

Figure 6.17- Launch Bearing (Photo courtesy ofPSM Construction USA, Inc.)

Figure 6.18- Launch Bearing and Launch Pads

Lateral guides are necessary to maintain the correct plan arrangement of the superstructure during

launch. They are placed beside the launching bearings surfaced with rollers or stainless steel (Figure 6.20). It is important to have locking devises to support the superstructure horizontally between subsequent launches, especially when launch is performed in an inclined elevation.


Page 16ofl8

Figure 6.19- Permanent Bearing which Serves as Launch Bearing (Photo courtesy of PSM Construction USA, Inc)

Figure 6.20- Lateral Guide at the Permanent Pier (Photo courtesy of Marco Rosignoli)

6.5.3 Launching stress mitigation system The front cantilever receives the greatest negative moment before the tip of the cantilever touches

a pier ahead of it. Three ways usually employed to mitigate this negative moment are: attach a light weight steel launching nose to the front end of the superstructure to reduce sectional force in the cantilever use temporary cable-stay system to support the cantilever from above place temporary piers between permanent piers to reduce the span length during launch


Page 17ofl8

(i) Launching nose Most of launched bridges are launched with a steel nose. Braced double plate girders are common structure for concrete bridges. It is tapered off toward the front end according to reduced sectional force it receives. Because it has to act monolithic with the superstructure, the connection is important to prevent detrimental gap. Usually it is connected to the webs of the superstructure by means of longitudinal post-tensioning. It is preferable to match-cast the first segment against the gusset plates at the end of the launching nose to make sure perfect alignment. As a rule of thumb, the length of the launching nose is around 65 to 70% of the maximum span to get the maximum benefit. Launching nose is transferred to the field in segments. They are assembled in front of casting yard before the first segment is cast. When a friction launcher is placed at the abutment, the superstructure is pulled onto the launcher through the launching nose. (ii) Cable-stayed system A second solution to reduce stress in the cantilever is supporting it with a temporary cable-stayed system. The pylon is hinged to the deck. Because of the need to continuously tighten and loosen the stays while launching and the complexity of calculation involved, the application is usually limited to long spans and well-trained crews. (iii) Temporary piers Placing temporary piers halves the spans and reduces the launch stresses. The scheme is to use a temporary pier at mid-span of the main span which is much longer than the others (as in Figures 6.4 and 6.20) or to use a temporary pier per span for long multiple spans as in Figure 6.1 0. This solution is particularly advantageous in combination with transverse shifting as the temporary piers are along the launch alignment only, and saving in prestressing is amplified. More temporary piers can also be used in the same span in the case of cable-stayed bridges- Figure 6.12.

6.6

Summary Incremental launching method is one of the most industrialized and effective forms of segmental construction. Large numbers of segmental concrete bridges have been successfully competed by incremental launching all around the world. Recent development of high-strength concrete, lightweight concrete~ and precast technologies can·· reduce launching weight and further reduce construction period. Further expansion of application is expected.

6.7

References (I) Rosignoli, M., "LAUNCHED BRIDGES: Prestressed concrete bridges built on the ground and launched into their fmal position", American Society of Civil Engineers, ASCE Press, 1998. (2) Rosignoli, M., "BRIDGE LAUNCHING", Thomas Telford, 2002.

<) Chapter 6.0- Incremental Launching of Segmental Bridges

Page 18 of 18

CHAPTER 7 ~·

-'\ .. )

Special Requirements for Construction of Concrete Segmental Cable-Stayed Bridges TABLE OF CONTENTS 7.0 7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.4 7.4.1 7.4.2 7.4.3 7.4.4 7.5 7.5.1 7.5.2 7.5.3.

)

'~

7.5.4 7.6 7.7 7.8 7.8.1 7.8.2 7.9

Cable-Stayed Bridges .................................................................................................................... 3 Introduction .................................................................................................................................... 3 Cable-Stayed Structure ................. o•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 3-4 Critical Construction Phases ......................................................................................................... 5 Deck, Stay Cable Stresses ....................................................................................................... 5-1 0 Unbalanced Loads .................................................................................................................. 11-12 Other Critical Construction Loads ................................................................................................ 13 Geometry Control ...................................................·.... :................................................................ 14 Casting Curves ....................................................................................................................... 14-15 Geometry Control for Prescast Box Girder Segments ............................................................ 15-19 Geometry Control for Cast in Place Box Girders ......................................................................... 20 Geometry Control for Cast-in-Place Flexible Decks .................................................................... 20 Stay Cable System Quality Control ............................................................................................. 20 Stay Cable Types ......................................................................................................................... 20 Bearing Plate, Recess Pipe lnstallation .................................................................................. 20-21 Stay Cable Pipe Installation ......................................................................................................... 22 Installation of Other Stay Cable Components ............................................................................. 23 Control of Stay Cable Forces ................................................................................................. 24-25 Fatigue Testing ............................................................................................................................ 26 Extradosed Bridges ................................................................................................................ 26-27 Design Concept ........................................................................................................................... 26 Construction of Extradosed Bridges ............................................................................................ 28 Conclusion ................................................................................................................................... 29 References .................................................................................................................................. 29 Notable Contrete Cable-Stayed Bridges in the United States ..................................................... 29

TABLE OF FIGURES Figure 7.1 Figure 7.2 Figure 7.3 Figure 7.4 Figure 7.5 Figure 7.6 Figure 7.7 Figure 7.8 Figure 7.9 Figure 7.10 Figure 7.11 Figure 7.12 Figure 7.13 Figure 7.14

Triangle Structure: Deck-Pylon-Stay Cable ........................................................................... 3 Beam on Elastic Support Analogy ......................................................................................... .4 Deck Rigidity ..........................................................................................................................4 Critical deck bending during construction .............................................................................. 5 Typical Erection Phases .........................................................................................................5 Neches River Bridge, Texas ...................................................................................................6 Sunshine Skyway Bridge, Florida ..........................................................................................6 Pasco Kennewick Bridge, Washington ..................................................................................7 Maumee River Bridge, Ohio ...................................................................................................? Centennial Bridge, Panama ...................................................................................................8 Dame Point Bridge, Florida ....................................................................................................9 La Plata River Bridge, Puerto Rico ........................................................................................9 Sidney Lanier Bridge, Georgia ............................................................................................. 10 Puente de Ia Unidad, Mexico ............................................................................................... 10

Chapter 7 -Cable-Stayed Bridges

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TABLE OF FIGURES (continues) Figure 7.15 Figure 7.16 Figure 7.17 Figure 7.18 Figure 7.19 Figure 7.20 Figure 7.21 Figure 7.22 Figure 7.23 Figure 7.24 Figure 7.25 Figure 7.26 Figure 7.27 Figure 7.28 Figure 7.29 Figure 7.30 Figure 7.31 Figure 7.32 Figure 7.33 Figure 7.34 Figure 7.35 Figure 7.36 Figure 7.37 Figure 7.38 Figure 7.39 Figure 7.40 Figure 7.41 Figure 7.42 Figure 7.43 Figure 7.44 Figure 7.45 Figure 7.46 Figure 7.47 Figure 7.48 Figure 7.49 Figure 7.50 Figure 7.51 Figure 7.52 Figure 7.53 Figure 7.54 Figure 7.55

Unbalanced Loads ............................................................................................................... 11 Aerodynamic Stability ........................................................................................................... 11 Aerodynamic Coefficients .................................................................................................... 11 Horizontal Yawing ................................................................................................................12 Vertical Rolling ..................................................................................................................... 12 Moment Resisting Pylon ...................................................................................................... 12 Stability During Construction ................................................................................................ 12 Twin Wall Pier, Sunshine Sky Bridge ................................................................................... 12 Stabilizing Cable, East Huntington Bridge ........................................................................... 12 Unbalanced Stay Loads .......................................................................................................13 Shear Lag During Construction ............................................................................................13 Effect of Superstructure Creep Shortening .......................................................................... 14 Long Term Deflections Dead Load ....................................................................................... 14 Pre-Cast Bridge.................................................................................................................... 15 Cast In-Place Bridge (Intermediate Cambers) ..................................................................... 15 Short-Line Casting Method ..................................................................................................15 Coordinate Transformation ...................................................................................................16 Out-of-Plumb ........................................................................................................................ 16 Deviation from Straight Line ................................................................................................. 16 Lift Segment ......................................................................................................................... 16 Stress Segment. ................................................................................................................... 16 Segment Shape Control ....................................................................................................... 17 Thermal Effect Stay Force Correction .................................................................................. 17 Plot Cantilever Tip ................................................................................................................ 18 Instrumentation .................................................................................................................... 18 Geometry Discrepancies L -170' ............................................................................................ 19 Stay Restressing .................................................................................................................. 19 Stay Bending ...............................................................................................................................21 Stay Cable Anchorage Layout... ...........................................................................................21 Recess Pipe Placed in Re-Bar Cage ...........................................................................................21 Steel Pipe Erection, Sunshine Skyway Bridge, Florida ........................................................ 22 Steel Pipe Erection with Highline, Maumee River Bridge, Ohio ........................................... 22 PE Pipe Erection with Messenger Cable, James River Bridge, Virginia .............................. 23 PE Pipe Supported with Strands, Puente de Ia Unidad, Mexico .......................................... 23 Anchor Set ...........................................................................................................................24 Stay Elongations ..................................................................................................................24 lsotension principle diagram ................................................................................................25 Mono Strand Jack ................................................................................................................25 Stay Cable Anchorage System ............................................................................................26 Second Vivekananda Bridge ................................................................................................27 Canada Line in Vancouver ...................................................................................................28


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Special Requirements for Construction of Concrete Segmental Cable-Stayed Bridges

<)

7.0 Cable-Stayed Bridges 7.1

Introduction Cable-stayed bridges have been increasingly successful for spans as short as 300 ft (91 m) and as long as 3340 ft (1018 m). Modern bridges use multiple stay cable cables for ease of erection and to reduce the weight of the bridge decks. In addition, cable-stayed structures must now resist dynamic effects due to the loss of a stay cable, and this condition is easier to satisfy with close stay cable spacing. The structures are, therefore, highly indeterminate and, as a result, construction phases are more critical than for conventional bridges. The final state of stresses in the structure depends greatly on the accuracy of construction. Following the initial choice of material for a cable stayed bridge superstructure, the next decision to be made by the designer is the method of construction for the bridge. Assuming concrete has been selected, there are two main choices for construction: cast-in-place with traveling forms or precast segmental construction. Precast Segmental Construction can be used very efficiently under the following conditions: • Superstructure segments are often heavy (130-300 t) unless the superstructure is divided into twin box girders. In the case of heavy segments, easy access to the site must exist, preferably by barge. Precast segments can be erected by a floating crane for low-level bridges. For high level bridges, it is easier to use a "beam and winch" system where the segments are lifted off barges with a winch system on the deck. The segments can also be delivered from the top if their weight is not excessive and erected with a derrick or crane on the deck.

)

• Manufacturing large precast segments requires a significant initial investment for casting yard, moulds and lifting equipment. This investment can be justified if a sufficient number of segments have to be built. • This is the reason why most precast concrete cable-stayed bridges are relatively long bridges or bridges where the cross section for the approach spans superstructure has been extended into the main span (e.g. James River Bridge, C&D Canal Bridge, Maumee River Bridge).

7.2

Cable-Stayed Structure The structure is made of three main components: Pylon, Deck, and Stay Cables. It can be assimilated to a triangular truss, with the deck acting as the bottom chord. The stay cables are stressed at the time of erection in order to balance the weight of the deck. For subsequent loading conditions, the stay cables act as passive structural members like the pylon and the deck. Fignre 7.1 Triangle Structure: Deck-Pylon-Stay Cable Pylon Stay Cable F

F

Deck

;---1

c:ti.IIJ~~:I::d~ 1

w


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Such a structure is often assimilated as a beam on elastic supports. The stay cables can be modeled as springs which are pre-compressed at the time of erection to provide adequate support to the deck without excessive bending. The amount of "pre-compression" of these springs will be essential in determining the stresses in the structure at the end of construction. Usually the designer balances the dead load shear with the stay cable forces to limit bending stresses in the superstructure. However, stay cable forces can be adjusted to counteract bending due to long-term creep, superimposed dead loads or live loads.

')

Figure 7.2 Beam on Elastic Support Analogy F ... PxllL

AL

j j Uniform Load P

2K

Stays = Springs Precompress at time of Assembly

There are two main categories of modern concrete cable-stayed bridges: 1) "Rigid" superstructure: Box girders belong to this category. The box girder is used when high torsion rigidity is required: for instance, when the structure is supported with a central single plane of stay cables. Box girders may also be used to improve the aerodynamic stability of the bridge. 2) "Flexible" superstructure: This type of deck may be used when two or more planes of stay cables support the superstructure and provide resistance to torsion. The ratio of inertia between these two types of structures can be as much as 1/10. Evidently, the flexible deck will accept more easily imposed deflections but will be more sensitive to instability under high compression loads. The dead load of these two structure types is usually equivalent. Only steel or composite decks are lighter. Figure 7.3 Deck Rigidity

I Stay I

vis;,.

I Stay

I Stay

$22

4000 Ft4

I

I

2 2 2 2

2 2 2 2 ?

2 2 2 2$

r" 3oo Ft 4 Chapter 7 -Cable-Stayed Bridges

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)

7 .3. Critical Construction Phases 7.3.1 Deck, Stay Cable Stresses It is essential that all erection phases be reviewed to ensure that stresses are within allowable limits at each construction stage. The typical erection cycle of a segmental concrete cable-stayed bridge consists of alternately erecting/pouring segments and stressing stay cables. At the time of segment lifting or pouring, critical stresses are usually reached: • Maximum negative bending in the deck. • Maximum tension in the last erected stay cable (maximum allowable 0.56 Fpu versus 0.45 Fpu in service). Figure 7.4 Critical deck bending during construction

T

Deck Moment Curve Elevation

)

Rigid superstructures provide for a better distribution of the loads among the previously erected stay cables, which also reduces the negative moment in the deck when pouring or lifting segments. Segment lengths are also normally shorter for precast segments to limit the segment weights and/ or allow for trucking the segments. In this case, the stay cable spacing is divided into two or three segments, allowing for re-stressing of the stay cable in-between lifts and further reduction of the moments in the deck. Stay cable forces and deck bending moments during construction are also more critical with heavier erection equipment such as cranes on deck. Figure 7.5 Typical Erection Phases

1) Lift Segment

3) Lift Segment

2) Restress Stay

4) Install & Stress Stay


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Figure 7.6 Neches River Bridge, Texas

Figure 7.7

Sunshine Skyway Bridge, Florida

Photos Courtesy of Figg & Muller Engineers

Chapter 7- Cable-Stayed Bridges

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Figure 7.8 Pasco Kennewick Bridge, Washington Photo Courtesy of David Goodyear

Figure 7.9 Maumee River Bridge, Ohio Photo Courtesy of Bilfinger & Berger


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Figure 7.10 Centennial Bridge, Panama Photo Courtesy of Bilfinger & Berger

With flexible superstructures, the segments can be as long as 35ft (10.7 m), corresponding to the stay cable spacing. In this case, the deck moment and stresses in the previously installed stay cables must be reduced. For instance, the stay cable can be connected to the traveling form and partially stressed prior to pouring the segment. Alternatively, the stay cable spacing and segment length can be reduced. For instance, the stay cable spacing and segment length were reduced to 17'6" for the Dame Point Bridge in Florida to facilitate construction operations.


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Figure 7.11 Dame Point Bridge, Florida

)

Figure 7.12 La Plata River Bridge, Puerto Rico Photo Courtesy of Las Piedras Construction


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Figure 7.13 Sidney Lanier Bridge, Georgia Photo Courtesy of Structurae

Figure 7.14 Puente de Ia Unidad, Mexico Traveling Forms for Edge Girders, Steel Floor Beams Photo Courtesy ofVSLMexico

Chapter 7 - Cable-Stayed Bridges

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7.3.2

Unbalanced Loads The overall stability of tbe partially completed bridge is critical. Cable stayed structures are usually built by tbe balanced cantilever method and the cantilevers can reach exceptional lengths. This makes tbe occurrence of dissymmetrical wind conditions on each side of the pylon more likely. Also, unsymmetrical dead loads result in critical moments in pylons and foundations. The main loads to be considered for overall stability during construction are: • • • •

Unbalanced segment Unbalanced dead load Unbalanced horizontal and vertical wind Unbalanced construction loads.

At ultimate conditions, tbe dynamic effects due to the loss of a segment and/or erection equipment on one cantilever must be taken into account. Load combinations for checking stability during construction can be found in AASHTO LRFD, Art. 5.14.2.3.2. Horizontal and vertical wind loads during construction should be developed through wind tunnel testing or analytical wind studies. Figure 7.15 Unbalanced Loads

QE

) DL-1%

DL+ 1%

CL + SPSF ~~~:::11=~~=:= CL + 10PSF WL - SPSF WL + SPSF The aerodynamic stability of tbe structure during construction must also be checked. Favorable deck damping helps the aerodynamic stability. Length/width and width/thickness ratios influence the behavior of the structure under wind conditions. The flutter effect is avoided with a proper torsion/bending rigidity ratio. Streamlining of the deck, for instance by using fairings along tbe edges of the deck, is another efficient way to improve the aerodynamic stability of the bridge during construction as well as in service. Figure 7.16 Aerodynamic Stability

L

,.

< 20B

Figure 7.17 Aerodynamic Coefficients Cx = Drag Coefficient Cv = Uplift Coefficient 2 C=C +C Y2 R X C, = Torque Coefficient

L

8;;. 101-1

IWr > Chapter 7 -Cable-Stayed Bridges

l!.5Wvl

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Wind on Long Cantilevers

~ + • •

____ , ----

_..J

t t t ' Figure 7.18 Horizontal Yawing

Figure 7.19 Vertical Rolling

There are several ways to resist unbalanced loads during construction: • Design a moment resisting pylon, for instance with twin walls. • Use temporary cables anchored in the pylon foundation to reduce moments in the pylon section at deck level • Use temporary cables connected to outside anchors to reduce moments in the pylon foundation and control buffeting • Use temporary cables connecting the top of the pylon to outside anchors, thus reducing unbalanced moments in pylon and foundation

Temp. Stay

Temp. Stay

@

CD

Section

~

Fignre 7.20 Moment Resisting Pylon

Figure 7.22 Twin Wall Pier, Sunshine Sky Bridge Photo Courtesy of Figg and Muller Engineers Chapter 7 -Cable-Stayed Bridges

Figure 7.21 Stability During Construction

Figure 7.23 Stabilizing Cable, East Huntington Bridge Photo Courtesy of David Goodyear

\J 12 of29

Unbalanced loads are also critical for stay cable anchorages at the pylon. With saddles, sufficient friction must be provided between stay cables and saddle pipes to resist the unbalanced loads with an acceptable safety factor as mentioned in the PTI Recommendations for Stay Cable Design, Testing and Installation, 5th Edition (PTI Recommendations),Art. 5.7.2.2.

Figure 7.24 Unbalanced Stay Loads Pylon Saddle

F+DF

7.3.3 Other Critical Construction Loads The shear lag due to horizontal distribution of stay cable forces is also more critical during construction than it is in service. Construction phases should be checked by assuming a 45-degree distribution of the horizontal component of the stay cable force, while the vertical stay cable force component is effectively applied at the stay cable anchorage. This analysis usually shows the necessity of adding a temporary post-tensioning system toward the end of the cantilever in the areas located outside of the stay cable plane(s).

PlanView

~

Figure 7.25 Shear Lag During Construction

•

I

+

r-1 I

I /

/

/

/

•

•

I

I

I

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Entrainment effects must also be accounted for, especially when the backstay cables are anchored in a previously erected back span. Sufficient compression must be provided to prevent joint opening behind the stay cable anchorages.


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Stay cable vibration may occur during construction when the periods of vibrations of the stay cables and the partially completed deck are similar. Stay cable cables are also sensitive to wind/rain-induced vibrations during construction and in service (see PTI Recommendations, Art. 5.2). These vibrations must be studied carefully at the design stage; and wind tunnel tests should be performed to evaluate counter measures, which could include: • Hydraulic dampers at deck level. • Specially designed stay cable pipes with helix or dimples to limit the influence of rain on stay cable vibrations. • Steel ropes connecting stay cable cables to change their vibration frequency. The overall sequence of construction influences final stresses in the structure. The sequence of closing the bridge in the side spans and central span cannot be altered without a structural check: Secondary moments due to post-tensioning and moment redistribution due to concrete creep are influenced by this sequence.

In summary, all construction phases must be thoroughly checked before the start of erection. The analysis should take into account actual erection conditions and actual equipment loads. At the design stage, the feasibility of construction should be checked by analyzing one erection scheme; and the specifications should clearly outline the tolerances for deviating from this scheme.

7.4 Geometry Control Geometry control is an essential part of the construction monitoring process: adequate profile and alignment are required as for any other bridge; in addition, geometry control is an essential tool to verify that the stresses in the structure and stay cable forces meet design expectations.

7.4.1 Casting Curves Like for any other segmental structure, the segments must be cast by following a pre-established curve to ensure that the bridge profile will coincide with the desired profile after all short-term and long-term deflections have occurred. I ~Closure

\ Side Span

I·

'

·~··

f

~Pylon

·I·

eoo'

•1

[! [J_IP-

_ .. 3

Figure 7.26 Effect of Superstructure Creep Shortening

t.-

Figure 7.27 Long Term Deflections Dead Load

Casting curves are influenced by: • The loads applied to the structure: dead loads, construction loads and stay cable forces. • The characteristics of materials, (ie. concrete creep and shrinkage), Modulus of elasticity of the concrete, apparent Modulus of elasticity of stay cables including the non-linear effects due to sag. • The sequence and schedule of construction. Chapter 7 -Cable-Stayed Bridges

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']

If any of these factors differs from design assumptions, new curves must be developed. Figure 7.29 Cast In-Place Bridge (Intermediate Cambers)

Figure 7.28 Pre-Cast Bridge Casting Cnrve Definition Camber

=:::::::-~ Casting Curve Final Profile Casting Curve = Final Profile + Camber Casting cannot start until casting curves are developed, which requires knowledge of the final erection scheme, actual construction loads, and actual material characteristics. If creep tests are required, they should be made at the beginning of the project so as not to delay casting. Segment weights should be monitored at the site by checking member diruensions and concrete unit weight or weighing segments (if the segments are precast). In summary, it is essential to develop actual casting curves rapidly at the beginning of construction to avoid delays. These curves must be produced using a time-dependent software that takes into account the effects of concrete creep and shrinkage, steel relaxation, and actual construction phases and schedule.

)

7.4.2 Geometry Control for Precast Box Girder Segments Segments are usually match-cast by the short cell method. Each segment is equipped with 4 survey markers for elevation control and 2 for alignment control. The location of these markers is recorded in the casting cell reference system. "As-cast" plots are developed in this reference system. Figure 7.30 Short-Line Casting Method Matchcast Segment Fixed Bulkhead Internal Formwork

Wet-Cast Segment

Match-Cast Segment ;.

•sw,

..

NW,;, SWA.~I

1·1

y

cAs Cast

.

NW.4•1

® BenchMark (Elevation)

__-, 1 East Rivet o 'r-+""==·="-:''---'--'""_'f".l.i•_-·_•·p,L'-.1._ , Line

-0----

Fi

;E.;.

~

F;..

E·,

'

NEl SE.i•l

••

NEA•L


Casting Cell Axis ~-'N---

-

Fixed Bulkhead

_...(.;:

'

l

;---;1 ~~~I

West Casto ,.,~,f==="""""i'~-''-'---'-'-~'L.-'-1-• , Line T

o--- - -

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The as-cast set of data is then transformed into the reference system of the erection site by a simple matrix operation. Figure 7.31 Coordinate Transformation

I x; ,Y; I =

As-Cast Coordinates Coordinate

I X;, Y; 1 =Erection

[~]=[:~::- :~: ~·[:}[:]

Yj

A

.L.__L_ _ _ __ , _ _

X

It should be noted that a systematic error of only 0.001 feet on elevation measurements in the casting cell would result in significant discrepancies at the end of a long cantilever. The first segment of the cantilever must be placed accurately to avoid offsets at the cantilever end.

Deflections of the structure at each stage are obtained from the general time-dependent computer program. Adding these values to the as-cast survey marker elevations provides expected elevations at each stage of erection. Similarly, the geometry of the pylon must be controlled during construction to verify that the maximum out-of-plumb and out-of-straight-line values assumed in the design for this compression member are not exceeded. Pylon - Construction Tolerances Figure 7.32 Out-of-Plumb

Figure 7.33 Deviation from Straight Line I I

I

I I ITG~-- 20"''Q

H

I

I

I

R"' 2DOH

I I

\

\

The elevation of the cantilever end should be plotted at each phase against theoretical figures. Instant movements of deck and pylon should be measured when lifting a segment or stressing a stay cable and checked against theoretical figures. Interpretation of the results would give indications on the actual stiffness of the structure. Deck Deformations During Construction


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Bending of the overall cantilever can be checked by plotting actual and theoretical elevations at each joint at a given erection phase. Mter each deck survey, the verticality of the pylon should be checked. If the pylon is out of position, it means that the structure is subjected to unbalanced loads; and the deck survey would be affected by this condition.

It is imperative to check that the last erected segment is not warped. This is simply done by comparing readings of the 4 elevation survey markers after erection and in the casting cell. Figure 7.36 Segment Shape Control

aa A, B, C, D: Elevation Markers

/'lA - l'lD = /'lB - t.C t.A - t.B = .6D - t.C

)

The accuracy of the stay cable jacking force can also be checked by measuring variations of elevations of the same survey marker during a full erection cycle (segments lifting, stay cable stressing andre-stressing). Comparing the result with theoretical figures allows determination of a gain or loss of elevation for the full cycle. Loss of elevation could indicate a deficit of effective stay cable force or excessive downward deformation, for instance, because of additional segment weight. Since the total deck movement includes an equal number of upward and downward deflections, the influence of the actual structure stiffness on the results is reduced. The thermal gradients within the superstructure and between concrete deck and stay cables can affect stay cable forces. The nominal stay cable forces given in the design normally do not account for thermal effects. One solution consists of verifying and adjusting the stay cable forces early in the morning if the stay cable has to be stressed during the day-time in order to satisfy the contractor's operations. It is more practical to estimate the gradients at the time of stressing, for instance, with thermo-couples. At each stage of erection, a correction of stay cable force can be computed to account for loss due to thermal gradients. During the daytime, thermal gradients create a downward deflection of the cantilever. When the gradient dissipates, the cantilever deflects back up and it results into a loss of stay cable force. Therefore, when stressing during daytime, an increase of stay cable jacking forces is required. Figure 7.37 Thermal Effect Stay Force Correction t.F = AE x t.L

L

F - t.F

(Gradient)

t.L = t.V sin"'-


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Plotting of the cantilever end elevations at each phase gives a good indication of the actual stiffness of the structure. The deck deflects up and down under stay cable stressing and segment lifting. The amplitude of the deflections increases with the length of the cantilever. If the bridge is stiffer than assumed, the cantilever tip elevation will seem high after lifting a segment. After stressing a stay cable, the elevation of the cantilever will seem low. Modifying the stay cable forces to bring the deck to the theoretical elevation at each phase could result into unacceptable stresses in the superstructure. This explains why a cable stayed bridge with a rigid type superstructure cannot be erected following theoretical elevations only. In this case the erection should be governed by stay cable forces with a tolerance not exceeding +1- 5%. If cantilever tip elevations are low after stressing and lifting a segment, this is an indication that the whole cantilever is aimed low or is deflecting excessively. Figure 7 38 Plot Cantilever Tip

~0--

Stress Stay

1

I

I

&"< &

Lift Segment Bridge Instrumentation: Important information can be obtained by placing thermo-couples and strain gauges along the deck section. However, precautions must be taken to obtain valid results: o Gauges must have the proper accuracy to detect long-term strains. o Gauges must be installed properly and must not be disturbed during concrete pours. o They have to be distributed across the width and depth of the section so that "average" axial stresses can be estimated. o A "zero" reading must be taken just after erecting or pouring a segment. Effects of creep/shrinkage of concrete must be dissociated by testing shrinkage separately. • The concrete modulus of elasticity has to be estimated to convert strains into stresses. Figure 7 39 Instrumentation

~ I

0


Strain Gauge Strain Gauge + Thermocouple

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"J

Parameters Influencing Deck Deflections: A parametric study was made by the designers of the Coatzacoalcos Bridge (Mexico) for a 175-foot (53m) cantilever. It shows the sensitivity of the cantilever deflections to variations of design parameters. Geometry Discrepancies: Geometry discrepancies due to casting errors or inaccurate placement of the first cantilever segment can be corrected by using plastic shims in the match cast joints between segments. The shim thickness should not exceed 1/4 inch (6 mm) and fiberglass mats are usually applied to prevent epoxy sag in the thicker part of the joint. Figure 7 AO Geometry Discrepancies L -170' CAUSE

EFFECT -8MM

+10% DL

-10% CONCRETE E -10% INITIAL F-STAY

-10MM

-10% FINAL F-STAY

-44MM

DECK GRADIENT 10 C0

-30MM

TEMPERATURE DECK -5 C0

-2MM

GRADIENT STAY/DECK 5 C0

-12MM

E STAY -13%

-11MM

) Other geometry discrepancies due to additional segment weight or inaccurate stay cable jacking forces must be corrected by re-stressing the stay cables. Usually several stay cables along the cantilever have to be re-stressed to avoid excessive stresses in the deck or stay cables. Re-stressing the stay cables is a complex operation because the system is highly undetermined. The designer needs to calculate the jacking forces for each stay cable and re-check the stresses in the structure at each stressing operation. If the geometry discrepancy was due to additional weight, the stay cable forces will be adjusted higher and the designer needs to verify that allowable stay cable forces are not exceeded for the bridge in service. It is advisable to provide some additional stay cable capacity at the design stage to account for such construction variations. Figure 7.41 Stay Restressing

V1

F1

+

A2 1 F2

A3t F3

+

+

A22 F2

+

A:52 F3

= A13

+

A23 F2

+

A33 F3

V3


= A11

V2 = A12 F, F1

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7.4.3 Geometry Control for Cast in Place Box Girders The geometry control procedures differ slightly from the procedures used for precast box girders: local geometry adjustments can be made with the traveling forms instead of shimming the joints between precast segments. Like with precast box girders, geometry discrepancies due to additional segment weight or inaccurate stay cable jacking forces need to be corrected by re-stressing the stay cables.

7.4.4 Geometry Control for Cast-in-Place Flexible Decks Except for the initial casting stages close to the pylon, the deck elevations can vary greatly with a small variation of the stay cable force. At the same time, stresses in the deck are not affected significantly by variations of the deck geometry.lt is therefore logical to prioritize the deck geometry control over stay cable jacking forces. Variations of segment weights are then automatically compensated for but it is important to record the stay cable forces to verify that allowable stay cable stresses are not exceeded. Again, it is advisable to provide some additional capacity in the stay cables at the design stage to account for these weight variations. Since the erection procedure is guided by the deck geometry, it is essential to apply the stay cable jacking force at a time when the geometry of the structure is not affected by thermal gradients, that is early morning before sunrise.

7.5 Stay Cable System Quality Control 7.5.1 Stay Cable Types The stay cable Main Tension Elements (MTE) can be high strength bars, steel wires, or steel strands (PTI Recommendations,Art. 3.2). Parallel strands are used for the great majority of recent cable stayed bridges. Stay cables with parallel wires have the advantage of being more compact than the parallel strand stay cables and this can be an advantage to reduce wind loads, which is beneficial for long span cable stayed bridges exposed to high winds. Modern stay cable systems are made of individually protected strands or galvanized wires and do not require cement grouting, which has proven to be a difficult and costly operation in the past. There are different types of strand protection: • Regular or galvanized strands with corrosion inhibiting coating and individual polyethylene sheathing • Epoxy coated strands The stay pipes can be made of structural steel (stainless or three-coat protection system) or high density polyethylene.

7.5.2 Bearing Plate, Recess Pipe Installation The stay cable recess pipe is installed when casting the segment. Normally, the recess pipe is bolted or welded to the anchorage bearing plate at a right angle. Then proper orientation of the guide pipe should result in proper orientation of the bearing plate.

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Great accuracy is required when placing the guide pipe as it will dictate the stay cable alignment. Installation tolerances are provided In the PTI recommendations,Art. 5.9. The vertical and horizontal angles are especially critical, as offsets would create bending stresses in the stay cable. The anchorage adjustable nuts or shims are in contact with the bearing plate. The bearing area must be perfectly flat to avoid stress concentrations and deformation of the anchorage socket or adjustable nut.

Figure 7.42 Stay Bending

-X

dwF·····

I. • 2c<.· 4A

-

A

Figure 7.43 Stay Cable Anchorage Layout Drawing: Dywidag - Systems International

Figure 7.44 Recess Pipe Placed in Re-Bar Cage


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7.5.3 Stay Cable Pipe Installation Steel pipes have to be butt-welded. Many of the welds can be done with the pipe lying flat on the deck, while others have to be done with the pipe in an erect position. In either case, the detailed butt-weld procedure must be developed and approved. Random x-ray checks of the welds are recommended. PE pipes are welded together by fusion, using a special device to maintain proper pipe alignments. Different systems are used to temporarily support pipes prior to strand installation and stay cable stressing. They all have to be designed to prevent excessive bending of the pipes. The stay cable pipes can be supported from the previously erected pipes, with messenger cables or highlines, or by a few stay cable strands inside the pipe.

Figure 7.45 Steel Pipe Erection, Sunshine Skyway Bridge, Florida

Figure 7.46 Steel Pipe Erection with Highline, Maumee River Bridge, Ohio Photo Courtesy ofBilfinger & Berger Chapter 7- Cable-Stayed B1idges

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··--..._, )

.·/) Figure 7.47 PE Pipe Erection with Messenger Cable James River Bridge, Virginia

Figure 7.48 PE Pipe Supported with Strands Puente de Ia Unidad, Mexico Photo Courtesy of VSL Mexico

7.5.4 Installation of Other Stay Cable Components Stay Cable supplier instructions have to be followed strictly for the installation of the other stay cable system components.


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7.6 Control of Stay Cable Forces Stay cable stressing may be one of the most critical operations performed during construction. The adequacy of the final bridge profile and stresses depends on this operation. Hydraulic jacks used to stress the stay cables must be accurately calibrated. It may be useful to have a load cell available at the site to check the jack calibration periodically. As a minimum, a master gauge should be available; and jack gauges should be checked frequently. Measurements of stay cable elongations during stressing can be made to check the correlation between stay cable force and assumptions for stay cable elastic modulus and stiffness of deck and pylon. Theoretical elongation figures must take into account the following effects: sag variation, deck movement, pylon movement, and modulus of elasticity of the steel. With a parallel strand stay cable system, seating of strand wedges should be compensated for .at the · time of stressing to avoid an accumulation of losses in stay cable forces. This can be simply done by overstressing the stay cable by the amount of assumed anchor set prior to releasing the pressure in the jack. The strands should be marked to ensure that no strand slippage occurs after removal of the stressing jack. Modern parallel strand systems are un-grouted and the strands are individually protected. This allows for installation and stressing of the strands one by one, which greatly simplifies the operations at the site due to lighter installation and stressing equipments (monostrandjacks). The forces in the individual strands vary every time a new strand is stressed and stay cable suppliers usually determine the jacking force for the initial (pilot) strand from information produced by the bridge designer (total stay cable force and pylon and deck movements under a given stay cable force). The stressing procedure should also result into equal forces between the individual strands within a tolerance of+ 1-2.5% of the strand ultimate tensile strength. This can be achieved by continually monitoring the force in the pilot strand, and stressing each strand to a force equal to the force in this pilot strand.

Figure 7.50 Stay Elongations

Figure 7.49 Anchor Set Wedge

- - -'v- "'----'-~v

- 3/8"

IlL =

Strand

av

•In -< (

Deck Movement liH

y /

/

/

/ o<.

£..-''-'/~

J

4L

= 4H

oln o<

I I I

Pylon Movement


24 of29

Small stay cable force adjustments or stressing of short stay cables, must be performed by using the anchorage ring nut and a multiple strand jack. This is required when elongations are so short (less than 15 mm) that this would result into overlap of the wedge bite marks on the stay cable strands.

heam111 plate

an~;ho~age

L!O\:>;.

n = strand number Total -Force: n x F,~

1'110110Sflilflt1 j&l;k

I

T

Force per strand

' t . ., ~~~~::ffi'::.=:=_~~~

!

~~-- . --J

Figure 7.51 Isotension principle diagram Drawing By Freyssinet

Figure 7.52 Mono Strand Jack Photo Courtesy ofVSLMexico


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7.7 Fatigue Testing The specifications require fatigue testing of individual strands or wires, as well as fatigue testing of full scale specimens. This testing is time-consuming and should be initiated at the early stages of the project to avoid delays. The stay cable anchorage system must be first submit-ted and approved by the Engineer. After the testing procedure is approved, testing may start, subject to the availability of the special laboratory equipment. If excessive wire break-age occurs, and the test does not meet specification requirements, the anchorage may have to be modified and the whole testing procedure started over. Some stay cable anchorage components have to be installed when casting the segments.lt is, therefore, preferable to have the testing completed prior to casting stay cable segments.

~')

Figure 7.53 Stay Cable Anchorage System

)

7.8 Extradosed Bridges 7.8.1 Design Concept The concept of "extradosed" bridges was introduced by Pr. Jacques Mathivat in the late SO's. Extradosed bridges are externally post-tensioned bridges with cables placed outside of the girder, thus allowing greater eccentricity for the external cables. These bridges can be considered hybrids between typical post-tensioned box girders and cable-stayed structures. The cables are anchored or deviated in a short pylon, about half as high as a typical cable-stayed bridge pylon (10% L instead of 20% L). The greater efficiency of the external cables allows for a reduction of the girder depth and as a result reduced dead load. The girders carry higher compression forces than with a cablestayed bridge due to the shallower angle of the cables. The variations of stresses in the cables under service loads are limited (2.5% ofMUTS according to PTI Guide Specifications), and the cables are therefore not subjected to fatigue as with a cable-stayed bridge. Overall the structural behavior of extradosed bridges is closer to girder bridges than cable-stayed bridges, where the girder weight is almost entirely supported by the cables in the cable-stayed bridge.


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··~

Extradosed bridges have been used economically for spans between 100 m and 200 m. Spans up to 270m have been reached in Japan by using hybrid girders (concrete close to the pier and steel central span). Following are some interesting features of extradosed bridges • Reduced concrete box girder depth and lowered vertical profile • Variable depth box girders replaced with constant depth box girders resulting into standardization of precasting operations, reduction of precast segment weights. • Reduced pylon height compared to cable-stayed bridges, lower vertical clearance required. • Simplified cable testing requirements (low stress variations, no fatigue) • Higher cable allowable stresses (-30%) compared to stay cables.

)

Figure 7.54 Second Vivekananda Bridge Photo Courtesy of Second Vivekananda Bridge Tollway Company


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7.8.2 Construction of Extradosed Bridges The construction of extradosed bridges is similar to girder bridges since the external cables act more as post-tensioning cables than stay cables, since they do not carry the weight of the girder directly. The geometry is controlled during erection similar to a typical precast box girder: geometry discrepancies can hardly be corrected by re-stressing the cables since a large force increase would be required to move the deck vertically. The geometry control is even more critical than for a typical precast box girder because the cantilevers are normally longer for extradosed bridges. The erection process is typically more simple than for cable-stayed bridges because the cables are normally stressed once like PT cables. The short cables are also easy to instalL Due to the short height of the pylon, it is easy to inject the cable with cement grout. The cables must be replaceable and double pipe systems are used at the anchorages and saddles in this case. Individually protected strands, similar to stay cables can also be used to facilitate cable replacement. The cables for extradosed bridges are quite short and normally not sensitive to wind-rain induced vibrations.

Figure 7.55 Canada Line in Vancouver Photo Courtesy of Buckland & Taylor/VSL


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7.9 Conclusion

"j

The construction phases of a cable-stayed bridge are critical. Important decisions need to be made at the site in a timely manner to avoid construction delays. The presence of a team knowledgeable in the design of the structure at the site during construction is therefore essential.

References • FIP Congress 1986-New Delhi, Cable Stayed Bridges, Keynote Lecture by Fritz Leonhardt • Pouts Haubanes, Pr. Rene Walter-1985 • Construction and Design of Prestressed Concrete Segmental Bridges, Podolny-Muller-1982 • Construction and Design of Cable Stay Cable Bridges, 2nd edition-Podolny-Scalzi-1986 • PTI Recommendations for Stay Cable Design, Testing and Installation, Fifth Edition • AASHTO LRFD Bridge Design Specifications

Notable Concrete Cable-Stayed Bridges in the United States

)

Bridge Name

Location

Date

Main Span(Ft)

Benton

Washington

1957

170

CIP

Sacramento River

California

1977

180

CIP

Pasco-Kennewick

Washington

1978

981

PC, Edge Box Girders

East Huntington

West Virginia

1985

900

PC, Edge Girders, Steel Floor Beams

Sunshine Skyway

Florida

1987

1200

PC, Box Girder

Dame Point

Florida

1989

1300

CIP, Edge Girders

James River

Virginia

1990

630

PC, Twin Box Girders

Neches River

Texas

1991

640

PC, Box Girder

Talmadge Memorial

Georgia

1991

llOO

CIP, Edge Girders

Cochrane

Alabama

1992

780

CIP, Twin Box Girders

C&DCanal

Delaware

1995

750


Sydney Lanier

Georgia

2000

1250

CIP, Edge Girders

Maumee River

Ohio

2007

612.5


Penobscot Narrows

Maine

2007

ll61

CIP Box Girder

La Plata River

Puerto Rico

2008

525

CIP, Edge Girders

Pomeroy Mason

Ohio

2008

675

CIP, Edge Girders


Superstructure Type

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\J

TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 8.0 SEGMENTAL SUBSTRUCTURES

8.0

Segmental Substructures

3

8.1

Introduction

3

8.2

Project Examples

3

8.3

Precasting Operations

7

8.4

Erection Operations

10

8.5

Summary

11

Chapter 8.0- Segmental Substructures

I ofl7

TABLE OF FIGURES GUIDELINES FOR CONSTRUCTION OF SEGMENTAL CONCRETE BRIDGES CHAPTER 8.0 SEGMENTAL SUBSTRUCTURES

Figure 8.1

Garcon Point Bridge Pier Column Segment

4

Figure 8.2

Albemarle Sound Bridge Pier Column Segments

4

Figure 8.3

Wando River Bridge Pier Column Disassembly

5

Figure 8.4

Linn Cove Viaduct Pier Column Segment Erection

5

Figure 8.5

Garcon Point Bridge Pier Column Segment Erection

5

Figure 8.6

C&D Canal Bridge Precast Column Erection

6

Figure 8.7

Hoover Dam Bypass Colorado River Bridge Precast Column Erection

6

Figure 8.8

Precast Column Segment Reinforcing Cage

8

Figure 8.9

Matchcast Pier Column Segment Precasting Operations

8

Figure 8.10

Precast Column Segment Concrete Finishing

9

Figure 8.11

Footing with Keyway

10

Figure 8.12

Stressing Vertical Column Tendons

10

Figure 8.1

Box Pier Segment Dimensions

12

Figure 8.1

Box Pier Cap Segment Dimensions

13

Figure 8.1

Precast Box Pier Details I

14

Figure 8.1

Precast Box Pier Details II

15

Figure 8.1

Precast Box Pier Details Ill

16

Figure 8.1

Loop Tendon Details in Footings

17

r) Chapter 8.0- Segmental Substructures

2 of!?

8.0

Segmental Substructures

8.1

Introduction The development of precast segmental piers, extends the use of segmental technology to bridge substructures. The frrst use of precast segmental piers in the United States was likely the Seven Mile Bridge, built in 1982 and located in the Florida Keys. Since 1982, over a dozen bridges utilizing precast segmental piers have been successfully constructed, allowing bridge substructures to utilize the benefrts of precast!prestressed concrete. These benefrts include increased rates of construction, economy and durability. In many cases where site preparations, deep foundations or extensive repetition of common piers provide lead time for precasting piers, conventional cast-inplace foundations can be re-designed to precast segmental piers for a significant project savings.

8.2

Project Examples As pointed out in the introduction, many projects have utilized precast segmental piers. These projects are diverse and range from projects completed in the early 1980's to projects currently under construction.

Many of these projects utilize simple hollow rectangular piers. This is the case for the VarinaEnon Bridge, the James Burrows Edwards (Wando) Bridge, the Chesapeake and Delaware Canal Bridge, the Garcon Point Bridge, and the Hoover Darn Bypass Colorado River Bridge. Other structures have utilized a variety of shapes selected to meet structural, aesthetic and other project requirements. Among these structures are the Sunshine Skyway, Linn Cove Viaduct, Albemarle Sound Bridge and U.S. 183 Austin Bridge. Of interest is the James Burroughs Edwards Bridge over the Wando River. The construction sequence for the main span of the superstructure called for temporary piers in the side span. The contractor elected to use precast segments for these piers, that were later disassembled after construction of the main span and utilized for permanent piers elsewhere in the project. This innovative use of segmental piers resulted in a significant reduction of materials and construction cost. Another project of note is the Linn Cove Viaduct on the Blue Ridge Parkway in North Carolina. This project utilized hexagonal piers with concave surfaces to fulfrll the aesthetic requirements. Black iron oxide was added to the concrete mix that has allowed the piers to weather to the same color as the surrounding rock outcroppings. The Linn Cove Viaduct also utilized a unique construction placement for the piers. No heavy equipment was allowed on the terrain below the structure. Therefore, the superstructure was built forward in progressive placement until a pier location was reached. The pier column segments were then delivered across the completed portion of the superstructure and placed in final position from above.

Precast segments are also utilized in the Hoover Darn Bypass Colorado River Bridge. The contractor elected to use precast segments for the pier columns and the spandrel columns on the concrete arches. The colunros are engineered to slightly taper toward the pier caps. The tallest of the colunros is about 300 ft tall. The temporary pylons which support stay-cable system during the arch erection are precast as well. Because of their temporary nature, epoxy coating is not provided between the pylon segments.


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Figure 8.1- Garcon Point Bridge Pier Column Segment

Figure 8.2 - Albemarle Sound Bridge Pier Column Segments


4 of 17

Figure 8.3- Wando River Bridge Pier Column Disassembly

)

Figure 8.4- Linn Cove Viaduct Pier Column Segment Erection

Figure 8.5- Garcon Point Bridge Pier Column Segment Erection Chapter 8.0- Segmental Substructures

5 of 17

Figure 8.6- C&D Canal Bridge Precast Column Erection

Figure 8. 7- Hoover Dam Bypass Colorado River Bridge Precast Column Erection


6 of 17

8.3

Precasting Operations While there can be variations in precasting procedures based on the contractor's preferences, the basic operations can be sunnnarized as: • • • • • • •

pre-tie reinforcing cage set forms for match-cast pour and install reinforcing cage and post-tensioning ducts establish geometry by plumbing forms and match-cast segment, with corrections as required from previous match casting pour and cure concrete perform as-cast survey for new segment remove bottom match-cast segment to storage set new match-cast segment in the casting bed

Precast column segments are typically a constant cross-section. Therefore, the reinforcing is very simple and is typically comprised of a series of transverse sets and a series of vertical straight bars. The transverse sets have typically been ties consisting of smaller bars sizes. Tie requirements with current design codes have increased the density of ties, but the resulting reinforcing bar cages remain modular and readily tied in assembly jigs off line.

)

·~J Chapter 8.0- Segmental Substructures

7 ofl7

Figure 8.8- Precast Column Segment Reinforcing Cage Most precast column segments are cast in their actual vertical orientation. The segments are

match-cast to assure a precise fit for when they are epoxy joined during erection. The bottom segments are typically cast first and casting proceeds upwards with the top segments being cast last. The first segment in each column is simply cast in the forms at ground level. The next segment is match-cast on top of the first segment. The first segment is then taken to storage, the second segment placed in the bottom position and the third segment cast on top of the second. This cycle is repeated until the casting of all segments in a column is complete. The last segment is a pier cap segment and will typically have a solid section and special reinforcing to accommodate the bearings and distribute the bearing and post-tensioning forces to the overall cross-section. The set-up for a match-cast pour most often follows the following sequence. The core form (forming the interior void) is installed above and overlapping the match-cast segment. The reinforcing cage is then installed, along with the post-tensioning ducts. The exterior form is then

installed. The form and match cast segment are then surveyed into plumb positions. If there was a deviation in the as-built plumbness from the last match-cast pour, the next pour will not be set perfectly, plumb. Instead, forms for the next pour will be offset to compensate for the previous asbuilt survey and allow the column as a whole to track a vertical line. Note that two orthogonal faces must be monitored to assure plumbness in both directions.

J

Figure 8.9- Match cast Pier Column Segment Precasting Operations Chapter 8.0- Segmental Substructures

8 ofl7

) /

)

Figure 8.10- Precast Column Segment Concrete Finishing The placing of concrete is very simple, with concrete being placed directly into the top of the forms. With the segments cast in the vertical position, there are no slabs and only the small upper joint surface requires fmishing operations. All other surfaces are formed. The curing requirements are the same as for any other concrete element. The strength required to lift the segments to

storage is usually a nominal 2500 psi. Therefore, minimum strength for handling is readily achieved overnight and most contractors elect not to steam column segments. The precasting operations for precast column segments are very straightforward and a segment per

day can typically be produced in each form bed. The limiting factor is the time needed for the concrete to achieve minimum strength for handling. It typically does not take a full day for a three to four person crew to set up and pour a segment when the reinforcing cage is pre-tied.


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8.4

Erection Operations Erection of precast columns proceeds very quickly. As noted, there can be variations based on the contractor's means and methods, but the sequence that follows represents typical colwnn erection

operations. The first operation is to place and plumb the first segment on the footing. Typically a keyway, slightly larger than the segment cross-section is cast into the top of the footing. The first segment is placed partially down into the keyway, but a minimum joint of I to 2 inches is left between the segment and the bottom of the keyway. The segment is plumbed by survey and shimmed off the bottom the keyway to maintain the desired geometry. Accuracy required for this operation is a function of the height of the colunm, since any error in setting will be projected to the top of the column. Post-tensioning ducts between the footing and the segment are coupled. Finally, high strength grout is poured into the keyway to join the segment to the footing.

)

Figure 8.11- Footing with Keyway

Figure 8.12- Stressing Vertical Column Tendons


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After curing the grout joint, erection of the remainder of the segments can proceed. The segments are epoxy joined by placing epoxy on the top ofthe last segment just prior to setting the next segment. The segments are simply set atop the previous segment, as geometry has been established in the precasting operation. The segments are placed until either stability becomes questionable, or the contact time for the epoxy is approaching the spec limit. At this time vertical post-tensioning is applied to the column to achieve a minimum uniform pressUre of 40 psi for epOxy squeeze,_ or the minimum stress required for stability, whichever is greater. During erection, intermediate post-

tensioning is most-often achieved with post-tensioning bars. These bars can be temporary, or become part of the permanent post-tensioning system. Note that for shorter colwnns, the entire column can often be erected without an intermediate stressing operation.

After all the segments in a column are erected, the permanent vertical post-tensioning is stressed. While either bars or strand tendons are acceptable, strand tendons are most often used for the major permanent post-tensioning. These tendons typically have both anchorages located in the pier cap segment and loop down throngh the footing. They are double end stressed from the pier cap. Tendons internal to the concrete cross-section are typically utilized. However, tendons external to the cross-section and running in the interior void can also be used if part of the design (these are typically unbonded tendons, and require a different design basis than internal tendons). In either case the tendons are grouted after installation for corrosion protection. Five pages of detail drawings for precast box piers developed for use with the AASHTO-PCIASBI Standard Segments are included in Figures 8.13 through 8.17. A detail drawing of the tendon loop connection of precast segmental piers to the foundation is presented in Figure 8.18.

)

8.5

Summary Precast segmental substructures can be a very efficient solution when ever there is volume production of standard pier shapes. Precasting can also be the best solution for unique sections

that require high quality concrete or geometry control, and when there is a long lead time for deep foundations that allows the contractor to fabricate pier sections in parallel with foundation work. The major advantage of precasting piers is the speed of erection, which surpasses any available option. Contractor re-design of conventional foundations to precast segmental foundations is often an option. Given current design codes and standards, precast pier sections are most efficient in low to moderate seismic areas or for tall columns controlled by wind forces, where the major reinforcement can be post-tensioning. In high seismic areas, the high density of confmement

reinforcing required by current codes and the ductility requirements for plastic hinge design make precast box sections less practical. However, current trends in code requirements that base design on system response instead of section ductility will favor post-tensioned precast segmental

columns, so future use of this design option should become increasingly popular.


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Figure 8.13- Span-by-Span and Balanced Cantilever Construction Spans 100' to 200' ~Box Pier Segment Dimensions


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Figure 8.14- Span-by-Span and Balanced Cantilever Construction Spans 100' to 200' -Box Pier Cap Segment Dimensions


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Figure 8.15- Span-by-Span and Balanced Cantilever Construction Spans 100' to 200' -Precast Box Pier Details I


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Figure 8.16- Span-by-Span and Balanced Cantilever Construction Spans 100' to 200' -Precast Box Pier Details II

\J Chapter 8.0- Segmental Substructures

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Figure 8.17- Span-by-Span and Balanced Cantilever Construction Spans 100' to 200' - Precast Box Pier Details Ill

() Chapter 8.0- Segmental Substructures

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Figure 8.18- Loop Tendon Details in Footings (Drawing courtesy ofDywidag Systems International, Inc.)

"···) Chapter 8.0- Segmental Substructures

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TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE..SUPPORTED BRIDGES CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS 9.0 9.1 9.1.1 9.1.2 9.1.2.1 9.1.2.2 9.1.2.3 9.1.2.4 9.1.3 9.1.3.1 9.1.3.2 9.1.3.3 9.1.3.4 9.1.3.5 9.1.4 9.1.4.1 9.1.4.2 9.1.5 9.1.5.1 9.1.5.2 9.1.5.3 9.1.5.4 9.1.6 9.1.9.1 9.1.9.2 9.1.9.3 9.1.9.4 9.1.9.5 9.1.7 9.1.7.1 9.1.7.2 9.1.7.3 9.1.7.4 9.1.7.5 9.1.7.6 9.1.7.7 9.1.7.8 9.1.8 9.1.9 9.2 9.2.1 9.2.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.14.1 9.14.2 9.14.3 9.14.4 9.14.5

Segment Production Casting Yard Planning and Setup Introduction

Location Acreage Utilities Existing Buildings Water Access Existing Site Conditions Soil Conditions Drainage/Storm Water Plan

Wetlands Issues Securi1y Slip or Dock Conditions Receiving/Delivery Delivery of Segments Material Deliveries Site Preparation Local Permits-Developer Fees Grubbing and/or Clearing

Grading·Drainage, Runoff Foundations Procurement

Fonns Batch Plant Steam Generator Cranes (Gantry Cranes, Tower Cranes and Segment Haulers) Auxiliary Equipment Facilities Office Trailer Locations Form Locations Rebar Jig Locations Warehouse, Material Storage location Steam Generator Location, Piping Requirements Portable Toilet Locations Temporary Fuel Storage Trash, Scrap, Recyclables Post Casting Summary- Casting Yard Planning and Setup long line and Short line Forms long line Casting Bed Short line Casting Bed Match Casting Casting Curve Fabrication of Rebar Cage with Post-Tensioning Ducts and Hardware Installation of Post-Tensioning Ducts Handling the Prefabricated Rebar Cage Rebar Cage in Casting Cell Setting the Match Cast Segment Placing Concrete Finishing the Top Surface Curing Forms Special Situations - Elevated light Rail Construction Rail Construction LRT Electlification Crossover Construction Grounding Requirements LRT Conclusion

Chapter 9. 0 - Production of Precast Segments

3 3 3 6

6 6 6 7

7 7

8 8

8 8 8 8·

9 10 10 10 10 10 12 12 15 15 16 17

20 20 21 23 24 24 24 24 25 25 26 27 27 33 37 38

39 41 41 42 42 43 45 46 47

50 50 52 . 52 53

55

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TABLE OF FIGURES

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CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 9.0 PRODUCTION OF PRECAST SEGMENTS Figure 9.1a Figure 9.1b Figure 9.2 Figure 9.3 Figure 9.4 Figure 9.5 Figure 9.6 Figure 9.7 Figure 9.8 Figure 9.9

Figure 9.10 Figure 9.11 Figure 9.12

Figure 9.13 Figure Figure Figure Figure Figure Figure

9.14 9.15 9.16 9.17 9.18 9.19

Figure 9.20 Figure 9.21 Figure 9.22 Figure 9.23 Figure 9.24 Figure 9.25 Figure 9.26 Figure 9.27 Figure 9.28 Figure 9.29 Figure 9.30 Figure 9.31 Figure 9.32 Figure 9.33 Figure 9.34 Figure 9.35 Figure 9.36 Figure 9.37 Figure 9.38 Figure 9.39 Figure 9.40 Figure 9.41 Figure 9.42 Figure 9.43 Figure 9.44 Figure 9.45 Figure 9.46 Figure 9.47 Figure 9.48 Figure 9.49

Typical Casting Yard Layout Typical Casting Yard Layout Loaded Barge Ready for Shipment Material Laydown Design Critical for Productivity Marine Haulout Facilities Segmental Form Assembly Variable Depth Segmental Form Segmental Pier Form Gantry Cranes with Appropriate Lifting Frames Tall Segmental Forms May Require an Aerial Personnel Lift Wetcast Segment Ready to Cast Worker Safety Review of Workstations Rebar Jigs Rebar Cage Assembly Storage Yard Layout Accessible Storage for Segments Specialized Vehicle for Post-tensioning & Grouting Segments Typical Long Line Production Pakse Bridge- General View of the Long Line Bed Pakse Bridge - View of the Soffit Support Structure and Form Guide Rails BWI Curbside Expansion Ramps - General View of the Long Line Bed BWI Curbside Expansion Ramps- View of the Form Support Structure San Francisco-Oakland Bay Bridge Skyway- General View of Long Line Bed San Francisco-Oakland Bay Bridge Skyway- General View of a Long Line Bed Casting Cell (Short Line Method) Casting Cell (Short Line Method) Short Line Form for Lee Roy Selmon Crosstown Expressway Tampa, FL Bulkhead and Wing Forms, Lee Roy Selmon Crosstown Expressway Tampa, FL Wing Form Supports, Lee Roy Selmon Crosstown Expressway Tampa, FL Diaphragm Segment Form, Lee Roy Selmon Crosstown Expressway, Tampa, FL Diaphragm Segment Rebar Placement, Lee Roy Selmon Crosstown Expressway, Tampa, FL Completed Diaphragm Segment, Lee Roy Selmon Crosstown Expressway, Tampa, FL Simple Cantilever Casting Curve Casting Curve for Typical Cantilever Bridge Jig for Fabrication of Rebar Cage Handling of Prefabricated Rebar Cage Placing Concrete Use of Internal Vibrators for Compaction Finishing Concrete Surface Transverse Post-Tensioning of the Top Slab in the Storage Yard Stripping Forms Striking Match Cast Segment Formwork Device for Separation of Segments Segment With Northbound & Southbound Plinths to CIP On-Site Plinth Steel Added to the Rebar Cage CIP Plinths With Final Preparation Before Rail Placement Rebar Added for Center Mount OCS Pole Crossover Rail Layout Prior to Secondary Concrete Pour Grounding Wire Exothermic-Weld to Post-Tensioning Anchor Grounding Wire Exothermic-Welded to Access Hatch

Chapter 9. 0- Production of Precas1 Segments

4 5 7 9 11 12 13 14 16 18 21 22 23 24 25 25 26 28 29 29 30 31 32 32 33 34 34 35 35 36 36 37 38 39 40 41 44 44 46 47 48 49 49 50 51 51 52 53 54 55

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9.0

Segment Production

9.1

Casting Yard Planning and Setup

9.1.1 Introduction Essential features of a casting yards utilizing short line forming are shown in Figures 9.la aod 9.lb. The plaoning and decisions made at the start of a project can set the tone for the remainder of the job. Many preliminary decisions regarding the location and setup of a casting yard for a segmental bridge project should have been made during the bidding process. One or more potential locations should have been examined for acreage, existing site conditions, requirements

for site preparation, required equipment, site access both in and out, and site clean up at the end of the project. Once the project has been awarded, the preliminary decisions have to be expanded to ensure a

smooth and efficient start up. This chapter will outline the several "incidentals" that tend to be overlooked before the first casting cell arrives on site. As with most construction projects time is always the driving factor. This means ahnost innnediately after award, long lead items need to be ordered. This can be anything from casting cells to batch plants to steam generators aod cranes. The idea behind segmental bridges is to have the segments themselves waiting at the casting yard to deliver as required by the erector. The most obvious long lead item is the casting cells. These can take anywhere from twelve weeks

to six months for delivery, depending on the number offorms required and the complexity of the segments. It is during this time that the casting yard needs to be fmalized and prepared to accept the casting cells for erection upon their delivery. Site preparations can be as simple as

clearing/grubbing, and leveling and grading, or may include drainage installation, consideration of wet land issues, zonage requirements, utility installation, and docking issues if delivery is to be by

water. Another item that requires early consideration is personnel for the project. Project Managers aod/or Plant Managers are typically known at the outset of a project. However, the supporting cast will take time to assemble. The supporting cast will include the QA/QC inspectors, Surveyors, Form Crews, Reinforcing Steel Cage Crews, Crew for Transverse Post-Tensioning and Grouting, Finishers, Operators, aod the many auxiliary employees required to complete the daily work.

Chapter 9. 0- Production of Precast Segments

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Figure 9.la- Typical Casting Yard Layout


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9.1.2 Location 9.1.2.1 Acreage Minimum Size Based on Size/Quantity of Segments The property size required depends on a variety of factors, including: segment length and width, the gantry crane width ( determines storage area aisle layout), amount of space between stored segments for work crews, whether the segments will be stacked, hatching needs, and shipping area layout are factors that require consideration. IdentifY the various work stations and the anticipated footprint for each component of the casting yard. Assumptions concerning space requirements should be conservative, and all assumptions should be clearly stated in preparation of a bid. Workstation placement should have some flexibility without impacting work flow and production efficiency. Zoning Restrictions The property being considered should be discussed with local building officials to determine property usefulness. Due to the temporary nature ofthe casting yard, a zoning modification may be feasible in consideration of bringing jobs to the local economy.

9.1.2.2 Utilities Since the casting yard setup is usually on the critical path of every project, the property's utilities (including locations, sizes, and rated capacities) are necessary information before making any negotiations or commibnents. An assessment of the existing utilities and anticipated casting yard needs is vital to ascertaining initial setup costs and scheduling impacts. Existing

Electrical- The contractor's kilowatt requirements are necessary before discussions with the local utility company can start. If a batch plant will be setup, it's highly probable that a transformer addition or upgrade will be necessary. This can be a long-lead item, so the need must be identified early. Water- The contractor must determine the precise casting yard needs before existing water supply can be deemed acceptable. The batch plant needs, truck washout area, steam generator, and sprinkler system requirements for any new buildings. Every work station and task should be evaluated. Telephone- The contractor, subcontractors, engineering and inspection firms all require a phone system with multiple telephone lines. Internet- Internet service may be required for the casting yard's efficient operation, remote monitoring and possible web cameras. Required to be Installed Once the contractor has successfully obtained the low-bid award, the list of utility upgrades must be documented and each item addressed and managed. The list of utility upgrades should be included in the casting yard schedule to ensure completion is monitored.

9.1.2.3 Existing Buildings Any existing structures on the property can be a detriment to work flow and the importance of protecting the structure from operational hazards. Obtain a plot plan of the property and determine sensitive areas that impact work flow and storage capacity (i.e., septic tanks, catch basins, leach fields, fire hydrants, overhead lines, etc.). Once all aspects of the building's impact are shown on a plot plan, determine whether the property can still fulfill the project requirements.

Chapter 9.

O~Production

of Precast Segments

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6.1.2.4 Water Access Some precast segmental bridge projects are over deep water. In such cases, a casting yard setup with water access for barge delivery is a strong advantage. The contractor must review existing marine haulout facilities within a reasonable distance from the project (Figure 9.2). It is helpful to know segment size & weight, and delivery requirements of the project. This information will he needed to evaluate barge sizes, since vessel displacement is an important factor in analyzing a potential marine facility. The water depth analysis of a potential site must include tidal extremes, currents, maximum wind and wave action to envision the circumstances that would avoid a fully loaded harge from bottoming out or causing extensive structural damage to the dock facility. Also, the contractor should have a good understanding of slip width requirements, because depending on segment weight, the casting yard's gantry crane could be modified to handle both casting operations and marine haulout facility.

Figure 9.2 -Loaded Barge Ready for Shipment An existing docking facility is advantageous due to time restraints. For larger projects, a new reinforced concrete dock with upwards of !50-ton gantry crane pier could be fabricated, if timing allows for the permitting process. Carefully research Coast Guard, Environmental Protection Agency, and Army Corps. of Engineers, port authority, state and local ordinances to fulfill all the appropriate permitting requirements for construction, renovation, and shipping.

9.1.3 Existing Site Conditions 9.1.3.1 Soil Conditions Soil engineers should investigate areas proposed for development, analyze site and subsurface conditions and make recommendations for septic systems, grading, earth support, drainage, foundation design, concrete slab on grade construction, and site remediation (including problems that may arise from expansive soil). A soils report is typically required for building permits. During construction, the soils engineer may need to make further tests to make sure subsurface soil conditions are compatible with those observed in the initial investigation, and modify the design recommendations as necessary.


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9.1.3.2 Drainage/Storm Water Plan A preliminary study of the drainage conditions at the casting yard property is necessary to determine the existing physical conditions and structures which may contribute to flooding. The study should include drainage calculations to identify any problem areas. If storm water retention is necessary, arrange layout of retention basins to maintain work flow. Storm water retention basins, piping and structures must be designed to meet the loading demands of the casting yard layout. Consideration must be given to requirements for maintenance of detention basins.

9.1.3.3 Wetland Issues A local geotechnical engineering company will have records of designated wetland areas and site restrictions in regard to overall property usage. Outline the designated wetlands on the plot plan and walk the property. Check environmental restrictions and logical assumptions as to actual workable perimeters around the wetlands. Cranes and heavy equipment may not be compatible with the environmental restrictions, and thereby render the property useless.

9.1.3.4 Security Security needs and public safety are high priorities when considering a casting yard site. Local unemployment and crime statistics could alert the contractor to potential problems. The town board or city council members and the local chamber of commerce are good business alliances. Evaluate all the data and implement conservative measures to provide a safe and secure environment.

6.1.3.5 Slip or Dock Condition Once the marine haulout facility has been chosen, perform an audit of existing structural conditions, both above water and underwater. The audit should detail the intended purpose and operating limits of the dock area, including minimum and maximum vessel sizes. Also, the contractor should prepare an Action Plan documenting the necessary upgrades, including work safety, general maintenance, and vessel impact criteria. Each activity should be implemented and tracked on the casting yard startup schedule, depending on the bridge erection timefrarne.

9.1.4 Receiving/Delivery 9.1.4.1 Delivery of Segments Segment delivery is the primary determining factor for establishing the casting yard's distance from and allowable travel route to the project. Once the segment takeoff is complete, this shipment aspect must be developed. The maximum size and weight of the segments will affect the proper truck/trailer combination for delivery. The contractor can evaluate his existing fleet or discuss the project with a reputable trailer manufacturer or local trucking company. The state and local agencies responsible for transportation permits will need to be contacted. These agencies will evaluate allowable axle loads, axle layouts, and height or width restrictions within their jurisdiction. The contractor should convey the number of legally permitted loads anticipated and shipments per day. If multiple jurisdictions are involved, the contractor will need to negotiate an acceptable criterion. Also, discuss scheduling, signage, escorts, police details, convoy allowances, hours of operation, bridge survey requirements and restrictions, and any upcoming construction projects along the intended route.


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9.1.4.2 Material Deliveries Concrete batch plant location/delivery Typically, means of site delivery to a project are via concrete truck. If the contractor chooses an off-site concrete supplier, determine the concrete truck allocation needed to provide a steady casting cycle for the casting yard. If a batch plant will be erected at the casting yard, determine conveyance means to the forms. New and used concrete trucks are readily available, acceptable truck criteria will depend on whether a central mixer will be part of the batch plant. Other avenues to explore will depend on how the concrete will be conveyed to the casting cells. There are concrete pumps (truck-mounted and stationary), booms and conveyors, all available in a variety of sizes. Rebar Delivery/Trailer Storage Allow sufficient space for rebar supplier trailers, as one-half to a full span of rebar for each casting cell should be at the casting yard. Maintaiu trailers intact until proper ground storage of the rebar or small rebar jig trailers come available. Detailed procedures will ensure an efficient operation. Embed Deliveries-Scuppers, Inserts, PT Duct The post-tensioning supplier, mechanical subcontractor, and electrical subcontractor will be providing many embedded items for the casting operation. Means of delivery, overall project quantities and breakdowns, scheduling restraints, and material storage requirements must be discussed in detail to properly plan material flow at the casting yard. Allocation of personnel and equipment to handle the daily workload, material storage directives, inventory control and documentation, and QC/QA interface must flow in an efficient, controlled environment.

Figure 9.3 -Material Laydown Design Critical for Productivity


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9.1.5 Site Preparation 9.1.5.1 Local Permits-Developer Fees The local building official and planning board can identify the necessary steps to achieve the building permit and the assessment of fees. depending on the properties (i.e., history, zoning, environmental concerns, easements, right-of-ways, and potential liens). If a zoning variance is necessary, assemble the proper local firms to provide assistance. Recommend the contractor know the number of jobs the casting yard will be bringing the community. Prior to lease/purchase of the property carefully walk the site with the most recent plot plan in hand. Identify all known and unknown elements on the property. Time is of the essence when building a casting yard, any unknown old foundations, catch basin, tanks, etc. can be very detrimental. Take photos to keep historical record of property and to plan site remediation prior to handing the property back to the owner after casting completion.

9.1.5.2 Grubbing and/or Clearing Before the site work starts, have a plan in effect that is based on the casting yard schedule. The contractor needs to focus the clearing efforts on the property areas requiring foundations. All surface objects, brush, roots, and other protruding obstructions, not designated to remain, and all trees and stumps marked for removal, shall be cleared and/or grubbed.

9.1.5.3 Grading-Drainage, Runoff Depending on property size and anticipated runoff, the project engineer might recommend a storm water catch basin system, pond or series of ponds. Either remedy can impact workflow and optimum land usage.

9.1.5.4 Foundations Choose the best soil bearing locations on the property for the foundations, especially for the forms and batch plant. Consideration should be given to whether the foundations are temporary or permanent. Be sure to contact Dig Safe prior to commencing sitework. For Offices Unless the contractor anticipates a long project, a level area with stable soils or slab-on-grade will suffice for temporary office trailers. Determine the total area required to house the project staff. If a wood frame structure, pre-engineered metal building, or masonry building is planoed, the soil bearing capacity will determine foundation requirements. If the structure will combine office and production, make sure proper firewall separations are incorporated into the design and the financial implications are determined upfront.

For Forms Determine soil bearing capacity and stability prior to receiving form layout and loads. Reviewing all the data and cost analyses will determine the type of foundation and any impact on scheduling. Since this activity is always on the critical path, the initial planning must be thorough.

i\J Chapter 9. 0- Production of Precast Segments

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Building Construction-Offices, Laboratories, and Inspector Facilities The local climate, project size and duration will determine building needs for the staff. If a substantial structure will be built, the early QC lab might be established in a temporary storage unit to start concrete mix design testing, etc. A detailed assessment of early casting yard activities and start dates for staff positions will provide background for an analysis of needs.

Existing Environmental Concerns A local building official or geotechnical engineering company should be able to answer environmental questions about the property being considered. If a batch plant will be setup, groundwater monitoring wells might be mandatory. Research any property restrictions and have a plan to implement the necessary steps to mitigate the issues (i.e., during development, while casting and final contractual obligations prior to property turnover). · Slip or Dock Renovations If dredging is required to regain water depth from an accumulation of silt and debris, once this is accomplished assess the structural condition of all revealed dock components. Document any additional renovations required and proceed with implementation of the Action Plan. The contractor should advise supervisors of all inspection milestones with all necessary parties. Also, the contractor should load test the facility and perform a 'dry ruo' of all operations.

)

Once the marine haulout facility is operational, maintaining and repairing infrastructure is extremely important, so perform periodic inspections to maintain a good structural status and functionality. To accomplish this task a maintenance program should be in effect with a detailed maintenance schedule.

Figure 9.4- Marine Haulout Facilities


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Existing Building Modifications

To the extent feasible, existing structures on the property could be used for office space, QC lab, material storage, and casting operations. The climate and project length will determine the investment cost-benefits of modifications. The cost factor of re-modification should be considered if the property needs to be restored back to its original condition. Employee Parking

Assign a suitable parking space with capacity for all employees and anticipated visitors. Use the appropriate barriers and signage depending on proximity to work areas and security level. Choose the site carefully; many aspects of casting yard operation are harmful to automobiles.

9.1.6 Procurement 9.1.9.1 Forms Purchasing precast segmental casting cells may determine the profitability of the casting yard operation. The contractor and casting machine manufacturers should thoroughly discuss what is included in the "Form Package." Items not included are unwelcome and expensive surprises during the erection of the casting inachines.

Figure 9.5 -Segmental Form Assembly


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Long line casting cells require a large footprint for the forms. The soffit is the full length of the cantilever and is built to the profile of the bridge. Details of the soffit form provide for geometry control. Side forms and soffit forms must permit adjustment for the deflection that will occur. Short line casting cells require much less area than long line machines. Horizontal and vertical adjustments are required for a short line machine. Geometry control requires the use of highly skilled staff and technical instruments.

Typical segment machines are the most critical production item in the casting yard. Therefore, it is critical to make sure the forms allow yard personnel to quickly and efficiently cast one segment per machine per day. Constant depth casting cells are the easiest forms to "turn" every day. The soffit width, and the web wall depth are constant. Segment length may vary, requiring that the match cast segment be moved on the soffit or that a soffit extension be used. Variable depth casting cells require the most changes to the forms to cast each segment. Changes in segment height and soffit width require additional time to prepare the casting machine for the next pour. In order to cast one segment per machine per day, the panels in the core form should be as light as possible so that the panels can be installed by hand. It is also recommended that an additional soffit be purchased to allow crews to assemble a day ahead to decrease change-over time each morning.

)

Figure 9.6- Variable Depth Segmental Form

All typical segments have rolling soffits and mandrels. High capacity rollers or crane wheels are used to position both pieces. The track and embeds to hold the rollers should be included in the form package. Soffits for the typical segments must adjust for horizontal curves and tight geometry control. Discuss both horizontal and vertical hydraulic options. Manual adjustment of the soffit and

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positioning frame generally requires too much time. Some casting cells come with two soffits and positioning frames, while others come with two soffits and one moveable positioning frame that

moves from soffit to soffit.


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Due to the large quantity of segments to be cast per cell, skin thickness of the forms is important. Steel for most soffit, web, and wing panels should be at least 1/4-inch thick. Placement of bracing for the web and wing supports requires base plates to be anchored to the foundation. The base plates and embeds should be included in the form package. Stripping the wing walls is generally performed by lowering/rotating the web and wing forms away from the segment. Make sure the forms will be able to move beyond any drain blockouts or enlarged wing tips without having to physically remove panels. Determine whether the forms can be moved manually or if additional hydraulics are required Shear keys can be fabricated from different materials. The most durable and costly shear key is machined from solid steel bar. Machined steel bar shear keys will withstand the abuse from the rebar cage dragging across them, and can be cost effective if used many times. Bent steel plate and ultra high molecular weight Polyethylene are other materials that may be used for shear keys. Both materials work well but are more susceptible to damage from rebar cages and misuse. The core form must be carefully detailed to ensure that a segment is cast every day. The ability to rapidly configure the core for deviation segments, top blocks and bottom blocks is criticaL Check with the form manufacturer to determine if removing a "pour by" panel will provide the deviation segment or if it is necessary to remove the core web panel and replace it with a panel that has the deviation blockout built in. Make sure all panels in the core have a slight draft (slope) incorporated to facilitate stripping. The core form may be retracted using hydraulics, moved manually, or a combination ofboth methods. Pier, expansion, and abutment segments require more time to set up for casting. The recess area of

these forms should be fabricated to facilitate stripping. Split Piers require a rolling soffit to move the half segments individually.

Figure 9. 7 - Segmental Pier Form


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9.1.9.2 Batch Plant Before evaluating the appropriate concrete supply method, determine the specific project requirements and where the casting yard will he located. Review the concrete material specifications and compare them with available local material resources. The project authority may publish a list of approved concrete material sources, including admixtures. Portable Batch Plant Portable batch plants are a convenient way of quickly setting up for casting. There are a number of national manufacturers that will provide the correct setup. Identify the number of cementitious materials you will be using. Judge the best available delivery method to the site and plant silos requirements, based on quantity per week usage and length of project. The quality and volume of concrete required for the project will determine cement and aggregate storage capacity needs, · along with central concrete mixer capacity. Review all the options of the computerized hatching control system. Local climate will dictate optional water chiller, ice machine, and boiler needs. Proper component choices and concrete material resources are the major requirements for producing high quality concrete. Proper component choices and concrete material resources are the central focus for consistent quality product and plant resale value.

\

. !

Carefully inspect manufacturer's proposals to determine what is included in each proposal. Missing items such as electrical wiring to components, installation of air lines, dust collection equipment, computer and OSHA safety equipment can be costly. Admixture manufacturers will usually price admixture storage tanks, pumps, and plumbing with electrical feed and air compressor "by others." Depending on installation requirements, concrete foundations and winterization needs are usually excluded. The batch plant will need weigh hopper calibration, which may be mandated by a State authority and NRMCA Certification prior to start-up http://www.nrrnca.org/. Contact the Concrete Plant Manufacturer's Bureau http://www.cpmb.org/MembersCPMB.htrn for approved manufacturers. Carefully review the local climate to avoid the pitfalls of excessive heat or extreme cold, both will need to be considered when present. Review state and local ordinances that can restrict batch plant design (i.e., height restrictions, noise ordinances, hours of operation, dust emissions, etc). Purchase from Local Existing Plant When the project is located within a town or city, review the cost benefits of having the concrete supplied by a local concrete plant. Make sure the local plant can provide the concrete mix using the specified material resources and be able to do so with equipment that meets project criteria. Determine any batch plant components that will need to be upgraded to handle segmental hatching requirements (i.e., central mixer size, cement silos, aggregate bins, admixtures, etc).

9.1.9.3 Steam Generator Size (BTU's) The steam-curing method typically used is live steam at atmospheric pressure for precast segmental concrete units. Steam curing at atmospheric pressure is generally done in an enclosure to minimize moisture and heat losses. Insulated tarpaulins are frequently used to form the enclosure. A typical steam-curing cycle consists of: (I) preset period, (2) a period oftemperature ramp-up, (3) a period for holding the maximum temperature constant, and (4) a period for decreasing the temperature.


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The steam generator size and output capacity will be determined by quantity of forms, form layout, and maximum concrete cubic yardage cast per day. In colder climates the concrete cubic yardage quantity should include the matchcast segments, since their temperature must be similar to concrete placement temperature. A 1,000,000-5,000,000 BTU unit will service most casting yard applications, with larger custom units available. The manufacturer will provide a piping design to optimize the unit; any variation on this design will drastically affect performance. The units can be outfitted with a variety of options ranging from simple manual controls to sophisticated computerized systems using thermocouples at each form. The latter can be progranuned to start

the unit after concrete preset, provide the correct ramp-up to optimum temperature, and ramp down the unit for proper release strength. Some computerized systems can be operated from the QC lab. Carefully weigh the cost benefits for each option, especially whether or not the equipment can be expensed over multiple projects. Also, check the hardness of the local water in case a water softener is needed as mineral deposits can gradually fill the steam lines and plug valves.

Alternate Curing Methods Some project specifications allow Type 3 cement usage during the winter months, which could

allow a reduced heat source and form insulation techniques to achieve accelerated curing. Fogging and water sprinkler methods should be used to maintain a humid environment. A fine fog mist is frequently applied through a system of nozzles or sprayers to raise the relative humidity of the air over tlatwork, thus slowing evaporation from the surface. Formwork can be economically insulated with commercial blanket or batt insulation that has a tough moisture proof covering.

When insulated formwork is used, care should be taken to ensure that concrete temperatures do not become excessive. Other options to investigate are electrical, hot oil, microwave and infrared curing methods which have been available for accelerated concrete curing use for several years. Electrical heating is especially useful in cold-weather concreting. Hot oil may be circulated under steel forms to heat the concrete. Portable hydronic heaters may be used to thaw subgrades as well as to heat concrete

without the use of an enclosure 9.1.9.4 Cranes (Gantry Cranes, Tower Cranes and Segment Haulers) Selection of a particular type of crane(s) for the casting yard depends on a variety of issues including casting yard complexity, productivity and overall cost-benefit analysis. Equipment choices largely depend on the daily tasks assigned to each piece of equipment.

!.,)

Figure 9.8- Gantry Cranes with Appropriate Lifting Frames


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Examine strongback and rigging needs carefully for safety and efficient operation. A site-specific safety manual and mandatory employee safety training is a key component of a successful project. When evaluating a gantry crane consider the following: • • • •

• • •

Lifting Capacity - Determine the maximum segment weight prior to selecting a crane. Also, make sure the crane will handle other uses or projects in the future. Overall Height- Identify any casting yard problems associated with the crane's height. Wheelbase- This criterion will establish the storage area Jane width. Decide on how segments will be stored and the maximize Jane capacity. Maxlinum Hook Height- Determine the maximum height a segment will have to be lifted above the ground, making sure to add the strongback and rigging. To lift a segment over segments in storage or lift a segment over a segmental form, these items will determine the hook height necessary. Turning Radius - Carefully determine cas.ting yard component layout using radius data. Traveling Speed- Useful information for unaerstanding task timefrarne and critical coordination factors. Drive Train- Casting yards typically have rough terrain; consider cost-benefits of all-wheel drive.

Every aspect of the casting, storage, and shipping operations will be controlled by the above factors. The particular aspects of the project requirements must be considered, any areas left unchecked could be costly. Review all federal, state, and local safety ordinances. http://www. osha. gov/SLTC/cranehoistsafetv/ Purchase

Regardless of the type of crane selected, there are many foreign and domestic manufacturers. Check product availability, service requirements, setup requirements (secondary crane), and include a manufacturer's list of recommended replacement parts in the contract. For smaller projects, a used crane might be suitable, especially a manufacturer's reconditioned unit. Lease

A new or used crane can be leased making the payments fully tax deductible operating expenses. For a larger crane size and relatively short duration, this option might be preferable.

9.1.9.5 Auxiliary Equipment Auxiliary equipment is available on the foreign and domestic market that will increase productivity and enhance coordination efforts. Analyze the cost-benefit data (i.e., purchase price, availability, longevity factors, parts and servicing, and warranty information) before making choices. Detennine all safety requirements and mandatory training programs required for the casting yard. The website for OSHA is: http://www.osha.gov/SLTC/poweredindustrialtrucks/ Telescopic Forklift

The rough terrain aspects of a casting yard are the perfect environment for telescopic forklifts. There are a number of manufacturers which produce telescopic boom forklifts. Their versatility is enhanced by numerous attachments applicable to casting yards (buckets, work platforms, rigid and extendable booms). Check maximum load height, load charts, specialized maneuverability options, precise load placement controls and ease of operation.

) Chapter 9. 0- Production of Precast Segments

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) Figure 9.9- Tall Segmental Forms May Require an Aerial Personnel Lift

Front-end Loaders

Front-end loaders are excellent all-around machines, especially with quick-disconnect bucket and options. This machine can keep the batch plant aggregate bins full, and by adding forks can load and unload tractor trailers. Front-end loaders may be used to keep the storage area and construction roads flat. Finally, they will move the air compressor, post-tensioning and grouting equipment around the storage area. With a variety of manufacturers and equipment sizes, frontend loaders are a versatile machine that is a strong asset to the casting yard. Compressors There are many uses for compressors in the casting yard, including air tools at the segmental

forms, batch plant needs, QC lab, and sandblasting needs. Since using air tools will increase labor productivity, a centrally located compressor with a suitably sized holding tank is warranted. After the casting yard layout has been determined, locate air supply line routes to each work zone. Determine where you will be sandblasting segment joints, etc., and whether it will be at one location or whether a trailer-mounted compressor should be purchased. Review all OSHA, state, and local ordinances regarding installation requirements.


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Survey Equipment

A one-second accuracy theodolite is used for centerline checks and elevation readings with a builder's level capable of reading to 0.001-foot using an invar rod. Project specifications should be carefully reviewed for requirements. Monopod setups for the instruments are normally used. In certain applications a station that covers the entire project may be advantageous. Winches, Screeds, Vibrators

Winches are a popular method for moving the matchcast segment to and from the casting position along the rails provided by the form manufacturer. Usually a pulley system is utilized on the opposite side of the form so that only one winch per segmental form is needed. The winch size is based on segment weight and coefficient of fiction of the rollers running along the rails, with an appropriate safety factor.

Screed manufacturers produce a variety of screeds that operate on air, gas, diesel, and electric. Each has benefits if used with manufacturer's recommendations. Carefully review the specific needs of your casting operation. It is important to remember that the concrete should already have been vibrated using other methods. The screed's purpose is to level and consolidate the top surface only. Two types of vibrators can be used in precast segmental (internal and external). Typically, only handheld internal vibrators are used, preferably in 18" maximum lifts. If the contractor is casting complex segments or congested rebar configurations, the additionai use of external vibrators can ensure proper consolidation and an aesthetic form finish. A small roller screed or air screed system to finish the deck surface is desirable.

)

Generator Generators come in a variety of sizes to assist startup and daily casting operations. Many casting yards are setup in remote areas where a small generator will be necessary to get the workers

started. Have the electrical contractor estimate total kilowatt usage of the batch plant, casting yard, and office needs. This information can be used to evaluate back-up generator requirements. To

ensure productivity in rural areas (especially areas subject to frequently black/brown outs), a large back-up generator can eliminate project delays. Sandblast Equipment The chief usage of the casting yard sandblaster is for light cleaning of the segmental matchcast joints prior to shipment. The joint faces must not be altered by this process. Depending on contractor preference, this task can be accomplished by a stationary or mobile setup. Review the project specifications and epoxy joint adhesive manufacturer's recommendation for required surface preparation to determine sandblasting equipment, compressor capacity, and sandblast material's composition and grit size.

Computers Desktops and/or laptops serve many uses at the casting yard. The most vital usage is maintaining

the daily geometry control software input/output to keep casting on target. The batch plant will have its own computer, tracking hatching operations and material usage. Office staff will be coordinating submittal status of a host of startup submittals for casting yard layout, equipment, materials, concrete mix designs and ongoing shop drawing approvals. Field personnel will be monitoring material inventory and purchasing requirements. The proper computer systems, software, and well-thought-out networking and internet linking requirements will promote a successful operation.


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Lab Equipment

The concrete specifications will detail the AASHTO, PC!, and ASTM standards to be followed during the approval and day-to-day casting operations. Since most projects are of short duration concentrate the on-site lab focus on the daily aspects of quality control. Specialized testing by an AASHTO-Certified Laboratory will be required for petrographic analysis of the course and fine aggregates, alkali-silica reaction tests, modulus of elasticity test, and creep and shrinkage tests; visiting the AASHTO website will list local certified labs. Prioritize the lab setup depending on the casting yard requirements. Usually the concrete mix design is the first task. Determine post-tensioning and grouting testing requirements. Some projects will require plant certification by PC! or NPCA. Both organizations will be helpful in concrete lab setup, preparing a quality control procedures manual, and addressing QC personnel certifications. The website address for each organization is as follows: • • •

htto://www.aashto.org/ htto://www.aci int.org/ htto://www.astrn.org/

9.1. 7 Facilities 9.1.7.1 OfficeTrailerlocations Unless the property has an existing office space that can be economically configured to the project needs, explore the availability of mobile office trailers which come in a variety of sizes and accommodations. Also, these trailers can be grouped together easily with stairs and decks to

)

produce a useful working environment

Troubleshooting and quick resolutions are key components of a well-run casting yard. The office complex should be suitable for all parties; in proximity to each other, close to the center of the casting yard, and near the QC lab. Inspectors Inspectors should have sufficient office space to review plans and specifications, each should have a desk, chair, locking file cabinet, phone and fax on larger projects, mobile radios, computers and

web access might be required. The larger and/or more complex projects will require detailed task assignments and close monitoring by senior staff. Surveyors/Engineers

These staff members will require everything listed above plus the use of custom computer setups with specialized software depending on project specifics. A 'Geometry Control Manual' should be issued to monitor daily operations. The precaster's surveyor and the inspector's surveyor should

each have their own geometry control programs to be able to make independent checks against each others set up numbers.

QA/QC Personnel

The ASCE Manual of Professional Practice "Quality in the Constructed Project" defines and discusses Quality Assurance and Quality Control as follows:

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"Quality assurance (QA), whether in design or construction, is planned and systematic actions necessary to provide adequate confidence that a structure, system, or component will perform satisfactorily and conform to project requirements. Quality control (QC) is specific procedures involved in the QA process." "If strict construction-related QA and QC guidelines are established, the project will be constructed according to the project's requirements, plans, and specifications. The owner is responsible for establishing the QA program appropriate for the proposed facility, and to provide adequate funds to initiate and maintain the program. The owner (or the official representative of the owner) should discuss the exact scope of a QA and QC program with the constructor before construction hegins. Owners should be knowledgeable and experienced in QA and QC, or they should retain professional advice in this field. 11 The quality control personnel will need to be near the QC lab and require plenty of work space depending on the casting yard workstations. Determine where the concrete will be tested, since many of the daily tests are made on plastic concrete. Many filing cabinets will be needed for cement and rebar mill certifications, individual segment files, shop drawings, submittal records, pre-pour and post- pour records. The QC lab will be outfitted with a compression machine for testing hardened concrete and grout cube testing. If the project specifications require 28-day concrete cylinders lab tests, a moist cure room is an economical alternative.

)

A 'Quality Control Manual' and 'Repair Procedures Manual' should be issued to provide daily operational procedures. 9.1. 7.2 Form Locations Each segmental form will require some servicing by crane and material handlers on a daily basis, thus, the casting yard layout needs to accommodate many tasks. Casting yard layouts will be controlled by the choice of equipment purchased.

J

Figure 9.10 Wetcast Segment Ready to Cast


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Figure 9.11 - Worker Safety Review of Workstations Foundation Requirements A casting yard location is usually chosen based on proximity to the project or due to availability of the appropriate size parcel. Once the property choices have been made and prior to casting yard layout, walk the property and examine soil classifications, water runoff patterns, and any evidence of existing contaminants. Next, excavate trial pits for soil samples and check bearing capacity to determine whether groundwater observations are necessary. When the ultimate bearing capacity is known from each of the trial pits, the casting yard layout can be developed. During the shop drawing phase of the casting forms and batch plant, the structural loads and layouts will be available to ascertain the correct foundation construction method for these structures. With the critical nature of the geometry control process, the casting forms must remain stable, so a conservative foundation design is mandatory. The diversity of site conditions can make it difficult to estimate a casting yard budget. Discussions with the local building inspector, site contractors and a geotechnical engineering finn will usually be helpful in this process. Survey Tower Review geometry control provisions to optimize survey equipment setup requirements, and devise a survey tower layout. Keep the survey tower layout simple, depending on the casting yard layout. Ensure the proper foundation depth and footprint is covered. When setting up multiple forms, try to utilize each survey tower for more than one form. This will reduce survey equipment needs, surveyor time, and speeds the casting cycle.

() Chapter 9. 0- Production of Precast Segments

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9.1. 7.3 Rebar Jig Locations

Casting yard layout is based on workflow efficiencies obtained by creating an assembly line enviromnent. Rebar jig assemblies can be constmcted of wood or steel depending on a variety of factors. A mioirnum of two rebar jigs is recommended for each casting form. Typical rebar jig assemblies must operate in a simple manner for daily cycling requirements. However, these jigs must adapt to the versatility of the casting form they serve. Prior to fabrication of rebar jigs analyze every segment configuration requirement to ensure smooth transitions. Most pier and expansion joint segments can be pre-tied to the top ofthe webs. This will accelerate the casting process, especially when the piers are starter segments for each span.

)

Figure 9.12- Rebar Jigs Rebar Delivery/Storage The rebar delivery method will depend on two factors: the economic restraints of the rebar fabricator negotiations, and the skill level of the contractor's work crews. Rebar can be delivered by the segment, a series of similar segments, or by the span. Additional options can be derived depending on fabricator's computerized order software. The rebar can be ordered by span, but anchor block reinforcement can be tagged for individual segments. Upon delivery, the various rebar bundles can be stored in a manner to ease transport to the rebar jigs. The rebar storage area should be close to rebar jigs. Transport of Rebar from Storage to Jigs In smaller casting yards the rebar is transferred from the storage area to the rebar jigs by a forklift. Larger projects utilize utility trailers or tower cranes to increase workflow. A rebar list for each segment should be used as a check sheet for delivery to each rebar jig. During the early stages of casting, sufficientlaydown area should be established for quality control checks of initial rebar deliveries and spot checking throughout the project.


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Figure 9.13 -Rebar Cage Assembly 9.1. 7.4 Warehouse, Material Storage Location In segmental construction, many of the embedded items are steel. These items require proper storage areas between delivery and ·usage to prevent corrosion. Depending on the climate zone, many manufacturers produce fabric structures, pre-engineered buildings, steel storage trailers, or an existing structure modified to meet demands. Proper organizational skills and inventory control procedures will maintain production casting sequencing needs.

9.1.7.5 Steam Generator Location, Piping Requirements Steam generator placement is critical to operational efficiencies. The steam creation chamber and the first six feet exiting the steam generator will be 250 degrees, which means building and worker protection is necessary. After initial steam pipe layout has been optimized, do not alter fabrication without discussing with manufacturer. In colder climates the steam generator will need protection from freezing temperatures. Shutoff valve layouts on multi-zone systems are critical for steam flow efficiency for remaining segmental forms in the curing cycle.

9.1.7.6 Portable Toilet Locations The proper OSHA, state, and local statutes will have to be followed to fmd the minimum requirements for the number of employees at the casting yard. In addition, identify congested work zones that may need additional facilities to keep productivity levels. Depending on number of employees and length of project, a large restroom facility with septic system may be cost effective.

9.1.7.7 Temporary Fuel Storage Propane, diesel, and gas storage on-site requires significant precautions. Research the proper storage area distance from the work zone mandated by OSHA, state, and local ordinances. Carefully follow all regulations, perimeter safety requirements, security fencing, and impact restraints. Sufficient total tank or tank farm capacity will depend on equipment usage, local


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temperature extremes, and hours of operation anticipated minus minimum tank pressure capacity

before equipment stops.

9.1.7.8 Trash, Scrap, Recyclables In keeping with sustainable guidelines, a 'Construction Waste Management Plan' should be issued for each segmental project. The casting yard will produce wastewater from the batch plant, excess concrete, excess rebar and strand, miscellaneous wood and paper products. Carefully identifYing approximate quantities of these recyclables during the project will assist your waste management procedures.

9.1.8 Post Casting

) Figure 9.14- Storage Yard Layout Once casting is complete there is still much work to be done to the segments before they are ready for delivery and erection. Once the concrete has reached a predetermined strength the transverse tendons require stressing and grouting. Inevitably, some cosmetic work will be required to ensure the segments meet appearance requirements. This cosmetic work could range from rubbing the

segment and lightly grinding the edges to any structural repairs that may be necessary. The final step is to lightly sandblast the faces to remove any laitance, dirt, debonding agents, etc. before segments are delivered for erection.

)

Figure 9.15- Accessible Storage for Segments


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To avoid multiple handling of the segments, much of this work can be done in the storage yard. Ideally, the segments of the same span should be stored together. This makes it easier to track spans that are ready for delivery, as well completion of the fmish work a span at a time without frequent relocation of crews and equipment. The key to setting up the yard is leaving enough space between segments to allow a scissor lift or man lift to maneuver between the ends of the segments and to have access to the transverse tendons with a stressing jack and pump. The crew will also need to get to the ends of the segments for grouting. The equipment being used will dictate the amount of room required between the segments.

Figure 9.16- Specialized Vehicle for Post-tensioning & Grouting Segments It is not unusual to have to rub the segments to repair unsightly bug holes. Leaving enough room to work around the segments with small hand tools is helpful. The worker should have access to the faces of the segments to allow lightly running a grinding wheel around the edges to remove any "fms" or burrs that may later create spalls when the segments are pulled together during

)

erection. As with most segmental construction projects, the casting schedule is driven by the sequence of erection. It is helpful to designate a row or series of rows in the storage yard layout for individual spans. This will make finishing much more efficient and will allow the loading crews to locate segments more quickly at time of delivery.

The overall purpose in setting up the storage yard is efficiency. The more efficient the yard crew and equipment operators are, the less money it costs to run the yard. Since there is never

unlimited access to equipment there is a risk of having a crew waiting for the crane to address their needs. If the yard is organized, it will not be necessary for workmen to spend time looking for segments at time of delivery. Efficiency is the key to a well-run yard.

9.1.9 Summary- Casting Yard Planning and Setup During the prebid of a precast segmental bridge project, a comprehensive plan for material, equipment, real estate, and personnel acquisition should be in place. Immediately after the letting, the successful low bidder should finalize and enact the prebid plan. The hiring of key personnel, negotiating with material providers especially long lead time items such as casting machines, and choosing vendors prior to an award insures that the casting yard can move quickly into production. Most vendors will start engineering the items they will provide with a letter of intent.


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Upon award of the project, write purchase orders to all of the vendors who have been working with a letter of intent. These vendors should be able to move directly into production, thus delivering the material more quickly than would be possible without the early commitments from the successful contractor.

9.2

Long Line and Short Line Forms

9.2.1

Long Line Casting Bed

The long line method refers to casting all the segments of a run by moving the form from one segment to the next without moving any segment.

A casting run can consist of either: • all segments of a span, when the deck has been designed to be erected span by span, or •

all the segments of one cantilever arm or both cantilever arms on either side of a pier when

the deck has been designed to be erected using the balanced cantilever method. When both arms are cast at the same time, the pier segment is also cast in the long line bed. This

particular set-up is shown in Figure 9.17. The long line casting bed usually consists of: • a bottom form or soffit which is fixed and has the same total length as the entire casting run. The soffit must be made in the profile of the structure with corrections for short-term and long-term deflections. In other words, the soffit is set to be cambered geometry or casting curve.

•

external forms, core forms and front bulkhead, which is one segment long and are moved along the run. When two cantilever arms are cast symmetrically there are two sets of movable

forms, one on either side of the pier segment. The external forms usually have a fixed height equal to the deepest segment of the run. The core forms and the movable leading bulkhead must be adjustable in height when the deck has a variable depth.

)

The long line method was the first method used for precasting segments as it has the obvious advantage that all the geometry control is done when constructing the soffit, thus simplifying this process during segment production. Traditionally, the soffit is fixed for the entire length, and the ground support is stiff enough that the settlements of any segment do not affect the achieved geometry. The long line forms used for the San Francisco-Oakland East Bay Bridge provided for adjustment in the soffit geometry as well as slight horizontal curvature. The disadvantages of this method are:

• •

it requires a large casting area it must be built on a firm, non-settling foundation

•

generally no allowance for smaller horizontal or vertical variations. In other words, all the

•

spans must have the same shape in their theoretical profile and alignment if the soffit is fixed, it can be made only for one casting curve, which must be used for all the

•

casting runs. In general, large variations in casting geometry are difficult to obtain the forms are rarely re-usable from one project to another

However, in order to make this casting method more practical for real bridge cases, some slight

variations have always been made. Particularly, the soffit can be divided into individual panels for each segment which are still supported by a common stiff foundation, but which allow some slight vertical adjustments by means of shims or screw jacks to suit differences in the casting curves.


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® r--0

Removal sequence

Segments being cast ·!&W@l§§llj

Segments corllpleled

)

Figure 9.17- Typical Long Line Production A recent example of the traditional long lines is the Pakse Bridge across the Laos-Thailand border (see Figures 9.18 and 9.19). The cantilevers were cast on a stiff substructure consisting of longitudinal concrete beams placed under the deck web, with external forms and core form traveling on side rails maintaining the horizontal alignment. In this case, the geometry of the

cantilever was controlled simply by setting the bulkhead to the correct height.


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Figure 9.18 -Pakse Bridge- General View of the Long Line Bed (Photo courtesy ofParsons)

Figure 9.19- Pakse Bridge- View of the Soffit Support Structure and Form Guide Rails (Photo courtesy ofParsons)


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To benefit from the obvious geometry control advantage of the long line method while compensating for its shortfalls, radical changes to the long line method have been made for two current projects:

For the curbside expansion at BW! Airport (Figures 9.20 and 9.21), the segments have a nontraditional shape as they consist of two lateral solid concrete beams with a large deck slab supported on steel transverse floor beams. The geometry of each run is different and complex, but a run consists of a maximum of four segments. The alignment is set prior to each run by fixing

curved rails to a stiff concrete platform following the theoretical aligmnent shape. The forms are then fixed to these rails and can be adjusted in height.

Figure 9.20- BWI Curbside Expansion Ramps- General View of the Long Line Bed (Photo courtesy of Par.>ons)


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-~

)

Figure 9.21- BWI Curbside Expansion Ramps- View of the Form Support Structure (Photo courtesy ofParsons)

) For the San Francisco-Oakland Bay Skyway Bridge replacement project, 44 cantilever arms are cast with the long line method, out of which 10 have a curved alignment (see Figures 9.22 and 9.23). The soffit form consists of individual forms for each segment, individually supported on short shoring towers which are set on a concrete slab but not fixed. Due to the weight of each segment (750T), the settlements are not negligible and must be considered to account for geometry control. A custom-made geometry control software was used to track the as-cast geometry and provide adjustments for the segments.


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Figure 9.22- San Francisco-Oakland Bay Bridge Skyway- General View ofLong Line Bed (Photo courtesy ofParsons)

Figure 9.23- San Francisco-Oakland Bay Bridge Skyway- General View of a Long Line Bed (Photo courtesy of Parsons)


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9.2.2

Short Line Casting Bed The short line casting bed is shown in Figures 9.24 and 9.25. With this method, the form is stationary while the segments move from the casting position to the match casting position and then to storage. Advantages of this method are: • space requirements are much less compared to the long line method • the entire manufacturing process is centralized • the system is extremely adaptable to geometry variations such as horizontal and vertical curvature and super-elevation transitions which are obtained without increase in costs • the forms are reusable for other projects. The disadvantage of the system is that the match casting segment must be very accurately placed. There is no tolerance for large casting errors. Illustrations of short line forms in use are shown in Figures 9.26 through 9.31.

Matr:h cas! segment

) Bulkhead

MovaU/e beams I o carry core

forms

Side forms (web & lYing forms) mounted on frame with sideways movement adjustment.

Figure 9.24- Casting Cell (Short Line Method)


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Bulkhead

--~il>ft

• Natatr-cul seamenf

'1:==~-- screWB/}ack Adjuslmenf

..-

Reils Figure 9.25- Casting Cell (Short Line Method)

)

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Figure 9.27- Bulkhead and Wing Forms, Lee Roy Selmon Crosstown Expressway Tampa, FL (Photo courtesy ofSouthern Forms, Inc.)

)

Figure 9.28- Wing Form Supports, Lee Roy Selmon Crosstown Expressway Tampa, FL (Photo courte.\y of Southern Forms, Inc.)

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Figure 9.29- Diaphragm Segment Form, Lee Roy Selmon Crosstown Expressway, Tampa, FL (Photo courtesy of Southern Forms, Inc.)

)

Figure 9.30- Diaphragm Segment Rebar Placement, Lee Roy Selmon Crosstown Expressway, Tampa, FL (Photo courtesy ofSouthern Forms, Inc.)


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.····'!

Figure 9.31 - Completed Diaphragm Segment, Lee Roy Selmon Crosstown Expressway Tampa, FL (Photo courtesy ofSouthern Forms, inc.)

9.3

Match Casting This is a method where fresh concrete of the new segment is cast against the already hardened concrete of the old segment. A bond breaker (usually a mixture of wax, soap, and talcum powder, but there are also chemical compounds) is applied to the hardened concrete surface in order to ensure that the segments will come apart. The match casting technique, as applied now on thousands of segments, is based on the fact that, provided proper precautions are taken, the segments will come apart cleanly, and, upon erection, will join together perfectly with the one joint being almost invisible. The precautions are merely the careful application of the bond breaker and the avoidance of jamming protrusions which make it physically difficult to break the bond. For correct fit at the time of erection, the joint faces must not have been altered, except for a light sandblasting. This generally means that no work can be done on the joint faces, and that segments must be stressed in such a way that differential deformation cannot occur.


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9.4

Casting Curve The casting curve is made up of two important components: 1.

The required geometric profile, which is actually the horizontal and vertical curvature and super-elevation shown on the plans, and

2.

The compensation of deflections. Both the deflections which occur during construction and the long-term deflections.

The deflections which occur during construction are shown in Figure 9.32. While erecting the five-segment cantilever shown in Fignre 9.32(a) in the five steps required, both self-weight and post-tensioning deflections increase as the cantilever increases. Fignre 9.32(b) shows the deflections after each step. The situation at the end of erection is shown in Figure 9.32(c). The combined effect of self-weight and post-tensioning will result in some deflection. To have a horizontal profile after this erection takes place, a casting curve should be provided which is precisely opposite the calculated deflection line. In Figure 9.33, structural deflections are shown combined with the geometric profile. The required geometry of the structure is shown in Figure 9.33(a). The deflections occurring during construction are shown in Fignre 9.33(b). The structural deflections are compensated in Figure 9.33(c), and finally added to the geometric profile of Figure 9.33(a) to form the casting curve in Figure 9.33(d).

A casting curve should be shown on the contract drawings based on the details and construction methods assumed in the design. The casting curve is verified and modified as necessary by the Contractor based on the details and construction procedures selected for the project.

fi 'i2 "Ia "IZ51 Figure 6.17(a)

Deflection dUe to canl.IJe-t~t&r post- tensioning Lh!-llec l.ion du~

to

selrJIJM'.ight Fig11re 6.1 ?(b)

Casting cl.trPe ror simple ··rree c.ant.iletl'er-

5

Figure 6-17(c)

Figures 9.32- Simple Cantilever Casting Curve


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9.5

Fabrication of Rebar Cage with Post-Tensioning Ducts and Hardware Prefabrication of the rebar cage, preferably with post-tensioning ducts and as much as possible of the hardware installed, is needed in order to achieve a production of one segment per day. This is readily accomplished by means of custom-built jigs and templates. A possible jig for a complete typical segment is illustrated in Figure 9.19. At times, it is more convenient to use partial jigs (i.e., one for the bottom slab and webs, and another for the top slab). By having several jigs, it is possible to fabricate rebar cages well in advance for segment production. The essential figures for a jig are: • walls and floors, of plywood or other suitable material, held rigidly by a frame to accurately define the main concrete surfaces (outside webs and slab soffits) • bulkhead templates cut and/or marked to the proper section size with standard post-tensioning duct locations accurately defmed • wing cantilever and templates marked and fitted with locators as needed for transverse post• • •

tensioning ducts, etc. spacer bars laced to the walls and floors to provide correct concrete cover to rebar adjustments for variable depth segments safety items, handrails, fall protection, etc.

Using a jig of this type also permits rebar, post-tensioning duct positions, and any other hardware locations to be accurately fJXed and marked up for repeated use. Duct profiles can be traced onto the walls to ease assembly, and so on. String lines are used to check rebar, cover and duct positions from open surfaces.

)

Required Btom..tric profile )

,c=

~

IT

II

Figure 6.18(a)

Figure 6.18(bJ

Caml>er={-0..~

I I

Figure 6.18(c)

Figure 9.33- Casting CulVe for Typical Cantilever Bridge


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Because segments can vazy a little in shape from each other, contain different post-tensioning duct and anchorage arrangements, and because the rebar cage will deform in transportation from the jig to the casting cells, final adjustments must be made after placing the cage in the casting cell. For pier segments, abutment segments, and expansion joint segments, the typical segment jig could be modified or a separate jig made. Sometimes the pier and expansion joint segments are cast in separate casting cells. In such cases, it nright be convenient to fabricate the cage directly in the casting cell itself. It is advisable to periodically check the accuracy of jigs and templates as they can deteriorate with repeated use and adjustments. Special care is needed when using epoxy-coated rebar in order to avoid damage to the coating during fabrication. The use of padding materials in the jigs and templates and padded slings will help. Damaged epoxy coating must be repaired using a "paint-on" epoxy.

Concrete cover spacers Bulkhead temp/ate Standard duct location

1"his illustrates a possible jig. Other types, including those far special segments might be needed. r:io1nelimes partial jigs and templates are more convenient, •.g. for top slab reinforcement

·na l only, bottom slab

reinforcement only, etc.

Soffits and outside surfaces

Figure 9.34 -Jig for Fabrication of Rebar Cage


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)

9.6

Installation of Post-Tensioning Ducts As mentioned in Section 9.5, most of the post-tensioning hardware and ducts are installed in the rebar cage, An exception to this is the anchomges themselves, which, because of their weight, are usually installed in the form.

All aspects ofiostallatiou ofpost-teusioning ducts and anchomges should be io accordance with Chapter 3 -Post-Tensioning Duct and Tendon Installation of the FHW A "Post-Tensioniog Tendon Installation and Grouting Manual."

9.7

Handling the Prefabricated Rebar Cage Tmnsportation of the rebar cage from jig to castiog cell should be done carefully to avoid excessive distortion. It is customary to use a special frame ( strongback) with hangers which can support the cage at many points (Figure 9.35). The rebar cage should be securely fabricated with adequate tie wire to maintain as much rigidity as possible.

)

Slings

Deformation and damage to rebar cage during transportation and handling can be minimized by using a special lifting frame and/or slings or similar.

Figure 9.35- Handling of Prefabricated Rebar Cage


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9.8

Rebar Cage in Casting Cell Once the form has been thoroughly cleaned out and oiled, the rebar cage with the post-tensioniog anchors is iostalled. The important items to watch for during anchor installation are orientation of the distribution plate, connection of plate to trumpet and of trumpet to duct, and also the position of bursting reinforcing. Ensure that the congested anchor zone can be concreted properly without fear of honeycombing. The orientation of the distribution plate is provided on the shop drawiogs, usually by providiog angle offsets to the plane of the form. Based on this information, recess pockets are to be made. In the case of many repetitive uses of the form, these recess pockets will be made of steel plates. Once a steel recess pocket has been checked for dimensional accuracy, it will consistently provide the correct orientation. Wooden recess pockets are for one-time use only, and these always need to be checked. Figure 3.15 in the FHWA "Post-Tensioning Tendon Installation and Grouting Manual" shows installation of an anchor and the proper alignment of the anchor with the duct. The alignment of trumpet and duct should be within a two-degree tolerance. The required bursting reinforcement is shown on plans (i.e., see Figure 3.11 of the FHWA "PostTensioning Tendon Installation and Grouting Manual"). The location of the bars should be strictly adhered to. Spirals should be centered properly in respect to the ducts and begio right at the distribution plate of the anchor. Dimensions for placement of hairpins are important, and these should be within one ioch. Particularly at the anchors, drawiogs should be iotegrated and show all reinforcing, tendons and hardware present in the area. All conflicts between tendons and reinforcing should be resolved by use of integrated drawings during the design process. Spirals are supplied closely wound, and should be stretched out to the proper pitch as shown on the drawings. Since anchor zones are densely reinforced, judgment should be made beforehand whether or not concreting will cause problems. If problems are anticipated, the Owner's Engineer (Construction Engineering Inspector) should be consulted. After placing the rebar cage and anchorage in the cell, all post-tensioniog ducts are securely connected to their respective anchorages and standard duct locations and alignments are checked. Care should be taken to provide adequate bottom support of the rebar cage. Final iospection of the tendons should be performed after the connection with anchors and match cast segments are made. Mandrels are installed as stiffeners in each duct and should extend through the entire length of the segment to prevent deflection during concreting operations.

9.9

Setting the Match Cast Segment This segment is usually set as close as possible to its desired position prior to placement of the rebar cage, then the rebar cage and ducts are properly adjusted, all inserts fixed, all post-tensioning anchorages bolted up to the forms, and the ducts connected. In order to ensure that there will be no mortar leakage, the match cast segment is checked and its position fine tuned after closing the form securely around the match cast segment. Refer to Chapter 10.0 on Geometry Control.


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9.10 Placing Concrete The class of concrete to be used in each element of construction should be as shown on the contract drawings. Concrete used to cast closure joints between superstructure segments should

be the same class as that used to cast the segments. Good concrete placing practice will ensure a good product. Some of the importaot points to watch

for are: I.

First, make sure that the forms are thoroughly cleaned, all joints are tight and sealed, all ducts are aligned and secure, and everything is in its proper place. The form should be lightly oiled for stripping, and the face of the match cast segment given a coating of a suitable bondbreaking agent.

2.

Place the concrete in the specified sequence (see Figure 9.36). A good placing procedure should prevent the concrete placed in the bottom of the web from spilling into the bottom slab. This movement of the web concrete can easily displace rebar and ducts and can pull

concrete away from heavily reinforced bottom anchorages or the web itself, causing honeycombing. Some flow of the concrete is unavoidable, but it can be minimized by using the following procedure, which is considered good practice. Other sequences of concrete placement have also been used successfully, and the procedure presented here is not intended to prohibit other practices which have provided good results. (a) The first concrete should be placed in the middle portion of the bottom slab, leaving about six to twelve inches clear of the side forms at the bottom of the webs. It is possible to do this by a delivery chute through a trap in the top slab soffit or by a chute through the bulkhead end. Concrete consistency needs to be flowable enough to fill congested areas, while stiff enough to avoid blowout of bottom slab during pours four and five (Figure 9.36). (b) Place the second concrete in the webs and compact it around the bottom comers to complete the bottom slab. Concrete lifts in webs are recommended to be no more than 24 inches in height. (c) Finally, place the concrete in the top slab working from the center and outside edges towards the web. Strike off the top surface and finish as described below.

3.

Use skips, chutes or pumps to deliver concrete, and do not let it fall from a great height as this causes segregation, and the impact can damage ducts and displace rebar. Concrete placement should be in accordance with approved procedures and specifications.

4.

Keep as continuous a delivery as possible; avoid holdups which can allow the concrete already placed to take on an initial set. Sometimes deliberate short waits are necessary, especially after placing the bottom slab and web comer concrete so that it can stiffen just enough to take the weight of the rest of the web concrete, but be careful that this waiting is not overdone to avoid cold joints. Often, use is made of retarders in the concrete mix to

simplify the casting operation. 5.

Make proper use of the internal "poker" vibrators to thoroughly consolidate the concrete. These types of vibrators should be pushed into the concrete for no more than two feet or so, and should slowly be withdrawn from the same location. Do not move the vibrator sideways while still in the concrete. Do not use the internal '"poker" vibrators to move concrete around

or to drag it from the webs into the bottom slab, for example, as this will cause poor compaction and honeycombing. Avoid contact of the vibrator with rebar and post-tensioning

)

ducts, as this will cause damage or displacement (Figure 9.37).


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6.

Make sure concrete is thoroughly compacted, especially in awkward areas such as the corners around heavily reinforced anchorage zones and within spirals. Sound compaction is essential.

7.

The fmish on the top surface should be accomplished by a screed. As this is usually the riding surface, great care is needed in fmishing. In spite of this being the last job for the day, it should not be hurried.

8.

Consult specific DOT requirements for placing and finishing concrete tolerancy and procedures.

t.oadi11g concn:~le fro-tn webs is uol

good prnctice.

Uf'LNQJ' Use 1nlt.>I'tlal

VJbr<•lor to rno,,e co/lcref(~. llus wUJ cause !JoneyconJbiiiC.

It

can d1slort rebal' cage. displace duels and cause

poor consolida lion.

Opening lor vibrator-seal lviU' trup.

Leave BH lo 12 .. clear of botton1 of inside web fortn for 2nd. and :Jrd loads.

Figure 9.36- Placing Concrete

• _QQ_Jj_QJ

mo>~ve~ii.i:i:,:~~~r;;::~

concrete around

Use internal

witiJ internal vi bra tors- it csn easily cause voids.

disturb interface

Risk of voids

vibrator to between loads and consolidate

llroroughly. ;:

2nd. l.oad

:•

1st. Load

• Avoid Jetting t.•ibrator go too deep. (It can cause aer-ation or voiding of earlier placed concrete whic!J has perhaps already started lhe setting process..)

• Also, vibrator con easily get stuck. • Avoid too muclr contact witll duels and rebar.

To consolidate concrete: pus/1 vibrator vertically into concr·ete to depll> of no more t!Jan 2FT (:t) and withdraw slowly, in steps, at l/Je same point. IYUhdraw vibrator from concrete to

move to another poinl~-JlO NOT drag vibrator through concrete. Vibrate at intervals of about IF't. lo

1"-6··.

()

Figure 9.3 7- U•e of Internal Vibrator. for Compaction

Chapter 9. 0- Production ofPrecast Segments

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9.11 Finishing the Top Surface A good quality finish of the top surface is essential as this is also the riding surface. The primary opportunity to achieve this properly is in the casting operation (Figure 9.38). A 1/2-inch sacrificial thickness for grinding or planing is now specified by some states, followed by mechanical grooving of the riding surface. To achieve a good finish by mechanical means, the equipment must be used properly by trained and experienced operators. Care is needed to make sure that all depressions are filled and all high areas removed to give a very uniform, dense and even surface. The surface must be accurate and should be as smooth as possible prior to applying any required riding surface treatment. After such treatment, the surface must still be even and accurate. Undulation should not be permitted. Hand finishing has been used successfully on many segmental structures in the past. Hand finishing requires that a good strong, straight screeding board be used extending from the top of the bulkhead to the top of the match cast segment to strike off the surface to au accurate level. Mechanical screeds also work very well. Good results have been achieved with both rolling and vibratory screeds. Mechanical screeding should be followed by a straight edge, usually a substantial, stiff aluminum beam, worked by hand and used to check and correct any low and high spots to give au accurate and straight surfuce from the bulkhead to the match cast segment. After surface wetness has disappeared, the surface may be very lightly "touched up" with floats to produce a finer and smoother surface. Floats should not be used in such a way as to move concrete or disturb the accuracy of the straight surface.

)

When frnishing a concrete surface, it is important to keep the concrete live for working by proper vibration, tamping and floating, and leave as if not to add water to wet any stiff areas. This will create patches of weaker surface material which will dust and wear badly in use. In order to take advantage of workable concrete, the initial leveling and frnishing should following immediately after placement. This is the best time to get the surface level. The best quality can be achieved by frnishing the segments to a smooth finish, and then providing a transversely grooved riding surface cut after erection of the structure. A small amount of extra cover is specified to allow for the depth removed by the grinding process prior to grooving. Be careful not to spoil the top surface when and if the concrete is to be covered for curing. (Use means to support tarps and prevent contact with top surfaces, etc.) The top surface of the bottom slab should be finished in a similar manner, although the appearance of the surface finish is not so critical, it should, nevertheless, be accurate. Mechanical screeds need not be used on the bottom slab.


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Use a mechanical screed to give accurate level from match cast. segment to bulkhead. Remove high spots, fill in low spots to unif01·m. dense, even surface.

After mechanical screed, use straight edge to check for and remove localized high and low spots fo give an accurate, dense and straight surface from bulkhead to rna lch cast segment. After surface wetness has disappeared, floats may be used very lightly to provide a smoother and liner surface.

4. Wearing surface lreatmenl. suciJ as grooving. is usually

done in IIJe field after erection.

Figure 9.38- Finishing Concrete Suiface

9.12 Curing In order to achieve a production rate of one segment per day from one casting cell, it is essential to ensure that curing is proper and sufficient to provide the necessary strength and control of shrinkage, etc. Project Specifications or Special Provisions prescribe the curing procedures to be followed. Curing procedures depend upon the type of concrete, its chemical hardening processes, temperature and exposure conditions. It is common practice to cover the segment with tarpaulins and apply steam to maintain a controlled temperature and humidity. Other methods have been used, including burlap, blankets, water, etc. With a production rate of one segment per day, clearly the curing process in the casting cell cannot be more than a few hours from the completion of the casting in the evening to the start of survey and stripping the next morning. This is why a controlled environment is essential. The segment curing may be obtained with chemical compounds or water, and should be in accordance with the contract documents.


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9.13 Forms Stripping of forms should not start until the concrete has reached the required strength. This is usually specified at 2500 psi. At this strength, it is normally possible to ease off the side forms, remove the core form, and pull back the match cast segment provided that the top slab is selfsupporting. At this strength, the segment could also be moved on its pallet but not lifted. In case the reinforcing provided is incapable of carrying the weight of the unsupported top slab at 2500 psi, then transverse post-tensioning must be stressed in full or in part. This would require a higher strength often specified at 4000 psi. It is customary to break cylinders in order to verify that these strengths are in fact obtained. Transverse post-tensioning of the top slab in the storage yard is illustrated in Figure 9.39. Stripping the forms should be done with care, as it is very easy to cause spalling and other damage when the concrete is young.

)

Figure 9.39- Transverse Post-Tensioning of the Top Slab in the Storage Yard Most casting cell forms are removable in whole pieces (Figure 9.40), but it is advisable to leave removal of any special block-out forms for as long as possible, as it is very easy to break the edges ofblockouts. Stripping and pulling back the match cast segment should be done with particular care. If the bond breaker has not been properly applied, portions can be broken off either segment. The shear keys are especially vulnerable. Also, the movement mechanism on the pallets must be examined

and understood by the stripping crew. Loosening of jacks and tilting of the pallet can "lift" the newly cast segment (see Figure 9.41). This motion can easily damage the shear keys and must be avoided. Segments may be separated by the following methods:


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• • •

heavy-duty steamboat ratchets hydraulic jacks either mounted on the soffit or manually (see Figure 9.42) hydraulic jacks on the soffit table and on the top deck through lifting blockouts

When concrete reaches required strength commence striking forms I. Disconnect inflated duct liners or mandrels 2. Remove wing bulkheads 3. Drop wing soffit and pull back web outside forms 4. Strike core forms, fold back and retract 5. Strike and pull back match cast segment (Use caution to avoid damage to shear keys, etc.- see Figure 9.41) 6. Pull segment back from bulkhead (Use caution to avoid damage to sbear keys, etc.)

-

1

2

Figure 9.40- Stripping Forms


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Inside formwork ~Bulkhead

New segment

/ / /

This key will not jam Tllis key wi/1 jam&- break

_ _--t;=ya--

CAUTIO!i;. In order to break the bond bet ween the matcb-·casl a.nd bulkhead. it is normal to

-release lhe rearward SC'rews/jack

to a/low segme11t to lilt back. Point of This can ca-use damage to sl1ear ro·talion keys. Grea-t care is needed wit li this operation. ll may be necessary lo try a few techniques depending upon the form m·ec-hanisms. 111er.e is

no simple solution.

) Figure 9.41-Striking Match Cast Segment

)

Figure 9.42- Formwork Device for Separation ofSegments (Photo courtesy of Southern Forms, Inc.)

Chapter 9. 0 -Production of Precast Segments

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9.14 Special Situations- Elevated Light Rail Construction An aerial guideway has all the standard issues of a typical precast segmental project with the added features for light rail operations. These light rail features will require additional review to determine cost impact. Coordination ofLRT systems integration work will require upfront planning and add to the normal QC/QA efforts throughout the project. The precast segments can be much smaller than highway units.

9.14.1 Rail Construction The rails (commonly continuous welded rail) may be directly fixed to the guideway with elastic fasteners or raised above the deck by using concrete plinths. Direct fixation rail

will necessitate tight construction

control. If plinths are shown, the contract documents will specify the design criteria, usually CIP once the structure is erected. Alternates to allow rebar couplers to avoid projected rebar or to allow the plinth construction at the casting yard may be present. The plinth layout will detail intermittent gaps to provide deck drainage. The requirements for concrete surface treatments for secondary plinth pour areas can prove

costly. Also, some upcoming projects are requiring the concrete plinth rebar to be fiberglass. Carefully review project specifications. The locations of specialwork, switchgear, high strength rail, rail expansion joints and rail anchors will require close shop drawing detailing. Address clearance issues with an RFI to avoid casting yard delays.

Identification of the design, location and installation requirements of all LRT features will be crucial. The system integration placement requirements will probably necessitate a fulltime electrician at the casting

yard.


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··~

Figure 9.44- Plinth steel added to the rebar cage

)

·..

)

Figure 9.45- CJP plinths with final preparation before rail placement


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9.14.2 LRT Electrification

···~

Methods used for traction power system electrification include a third rail or installing a series of overhead catenary lines (OCS) to operate the trains. Either option will add to the standard coordination factors at the casting yard. The industry does utilize AC and DC traction power systems. Most modern light rail projects are using DC traction electrification system (TES), so our focus is DC current.

Figure 9.46- Rebar added for center mount OCS pole

9.14.3 Cross-over Construction An aerial guideway with northbound and southbound tracks will detail a cross-over at certain intervals. The crossover area will be congested with additional rebar and systems integration requirements. ClarifY the tolerance requirements during the early stages of the project to avoid casting delays and QC/QA shortfalls. The segments in these tight construction control areas may not meet the daily casting cycle. A preconstruction meeting with the project LRT consultants is warranted prior to casting these segments.


52 of 55

Figure 9.47- Crossover rail layout prior to secondary concrete pour

9.14.4 Grounding Requirements

)

DC stray current can cause corrosion of the transit system infrastructure grounding safeguards will be built into the structure. The post-tensioning system and concrete reinforcement may have grounding system to

eliminate the cumulative effects of the stray current to increase the longevity of the structure. These measures will also ensure personal safety of the passengers, operators and maintenance crews. Proper

training of production crews and QC/QA staff will ensure competent work procedures are maintained.

•

Post-tensioning

The contract documents may require grounding the post-tensioning system due to stray current migrating to

the PT tendons. Each tendon will normally require grounding only at one post-tensioning anchorage. One method is to prep ao area on the backside of the post-tension anchor and attach the ground wire with an exothermic weld. The individual copper jumper wires can be crimped together and attached to the topslab reinforcement mat.


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•

Topslab Reinforcement The upper layer of reinforcement of the topslab may require grounding. One method requires tackwelds on all or a portion of this reinforcement mat. This will entail the use of ASTM A 706 weldable rebar, which should be specified in the contract documents. A ground wire is then attached with a crimping tool.

•

Miscellaneous Metals Project specifications could require all metallic embeds to be grounded, including patron barriers, hand rails, expansion joints, access hatches, etc. Grounding continuous items like handrails may mitigate the grounding requirement to every 40 feet. These requirements can be project specific. Verify if a copper jumper wire is necessary or addition rebar pieces and tie-wire will suffice. An item checklist with specific requirements and frequency will mitigate cost and inspection needs.


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Figure 9.49- Grounding wire exothermic-welded to access hatch No. 1 in the picture above shows the exothermic connection of the copper grounding wire.

)

No.2 is a styrofoam blockout that will enable the ground wires to be connected to the conduit system within the precast structure.

9.14.5 LRT Conclusion Light rail projects add to the complexities of segmental construction, but proper focus on details will prove successful. A methodical approach to the additional aspects oflight rail construction and suitable managerial oversight will mitigate the learning curve. Contractors and precasters should welcome this application of the technology.

·.) Chapter 9. 0- Production of Precast Segments

55 of 55

)

TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS 10.0 10.1 10.1.1 10.1.2 10.1.3 10.2 10.2.1 10.2.2

3 3 Lifting Holes Cast in the Top Slab of Segments 3 Inserts Embedded in the Segment Webs and Protruding Above the Top Slab 4 Lifting Slings or C Hook Frame 5 Handling and Transporting of Precast Segments in Precast Yard 6 Handling precast segment from the new-cast position to the match-cast position 6 Procedures for Handling, Transporting and Erecting Precast Segments

Methods of Lifting Precast Segments

Handling and Transporting of Precast Segments From the Casting Area to the Storage Area

)

10.3 10.3.1 10.3.1.1 10.3.1.2 10.3.1.3 10.3.2 10.3.2.1 10.3.2.2 10.3.2.3 10.3.3 10.4 10.4.1 10.4.2 10.4.2.1 10.4.2.1.1 10.4.2.1.2 10.4.2.1.3 10.4.2.1.4 10.4.2.1.5 10.4.2.1.6 10.4.2.2 10.4.2.2.1 10.4.2.2.2 10.4.2.2.3 10.4.2.2.4 10.4.2.3

Transporting Precast Segments from the Precast Yard to the Erection Site Transporting Precast Segments via Water Using Barges Loading Transport Unloading Transporting Precast Segments Off-site via Land Loading Transport Unloading Transporting Precast Segments On-site via Land Erection of Precast Segmental Bridges Factors for the Selection of Precast Segmental Bridge Erection Methods Erection Methods for Precast Segmental Bridges Erection Methods for Span-by-Span Type Bridges Underslung Trusses with Crane on Ground or Barge Mounted on Water Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck Erection with an Overhead Gantry Full Span Erection with Winches I Strand Jacks Full Span Carrier I Erector Full Span Erection on Shoring Falsework Erection Methods for Balanced Cantilever Bridges Balanced Cantilever Erection by Crane on Ground or on Water Balanced Cantilever Erection by Overhead Gantries Balanced Cantilever Erection with Beam and Winch/Strand Jacks

Balanced Cantilever Erection with Special Erectors Erection Methods Conclusion

Chapter I 0.0 Procedures for Handling, Transporting and Erecting Segments

6 11 11 11 12 12 14 14 14 15 15 19 19 21 22 22 24 25 27 28 29 30 30 32 34 36 37

I of37

I

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 10.0 PROCEDURES FOR HANDLING TRANSPORTING AND ERECTING PRECAST SEGMENTS

Figure 10.1 Figure 10.2 Figure 10.3 Figure 10.4 Figure 10.5 Figure 10.6 Figure 10.7 Figure 10.8 Figure 10.9 Figure 10.10 Figure 10.11 Figure 10.12 Figure 10.13 Figure 10.14 Figure 10.15 Figure 10.16 Figure 10.17 Figure 10.18 Figure 10.19 Figure 10.20 Figure 10.21 Figure 10.22 Figure 10.23 Figure 10.24 Figure 10.25 Figure 10.26 Figure 10.27 Figure 10.28 Figure 10.29 Figure 10.30 Figure 10.31 Figure 10.32

5 7 Straddle Carrier Transporting Segments to Storage. New Baldwin Bridge. CT 7 Gantry Crane on Rails, Singapore LRT Storing and Stacking of Segments 10 Double Stacking of Segments 10 Barge Transportation of a Segment Hauler 13 13 Barge Transportation of Segment Gantry Loading Segment on Segment Transport Vehicle, New Baldwin Bridge, CT 16 Truck and Segment on Trailer, New Baldwin Bridge, Connecticut 16 Delivery of Segment to Launching Gantry, New Baldwin Bridge, Connecticut 17 Segment Lifted by Launching Gantry, New Baldwin Bridge, Connecticut 17 Delivery of 85 Ton Diaphragm Segment for the Boston Central Artery Project 18 Crane Erection of Span-by-Span Bridges on Underslung Trusses 22 Crane Erection of Span-by-Span Bridge on Underslung Trusses 23 24 Span-by-Span Erection on Underslung Trusses with Crane or Deck Span-by Span Erection with an Overhead Gantry 25 Span-by-Span Overhead Gantry Segment Erection 26 Full Span Overhead Erection with Winches 27 Full Span Erection, James River Bridges, Rl 27 Full Span Carrier I Erector 28 Full Span Erection on Shoring Falsework 29 Full Span Erection on Shoring Falsework 29 Balanced Cantilever Erection by Crane 30 Balanced Cantilever Erection by Crane 31 Balanced Cantilever Erection by Barge Mounted Crane 31 Balanced Cantilever Erection by Overhead Gantry 32 Balanced Cantilever Erection by Overhead Gantry 33 Balanced Cantilever Erection by Overhead Gantry 33 Balanced Cantilever Erection with Beam and Winch 34 Balanced Cantilever Erection with Beam and Winch SFO Skyway Bridge 35 Special Erector Used on the Dallas High Five Project, TX 36 Special Erector Used on the Dallas High Five Project, TX 37 Handling Segments


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10.0 Procedures for Handling, Transporting and Erecting Precast Segments Regardless of the chosen erection method, the segments could be handled and transported multiple times. Typically, the segment will be handled and moved within the casting area, moved to the storage area, and from there the segment will be transported to the bridge site for erection. This chapter describes most of the methods that have been used in handling, transporting and erecting segments.

10.1

Methods of Lifting Precast Segments Precast segments can be lifted using one of the following options:

10.1.1 Lifting Holes Cast in the Top Slab of Segments Depending on the segment weight and design, 4, 8, I 0 or more bars may be needed to lift the segment. Lifting bars are typically high strength bars ranging in diameter from I W' to 3". The lifting bars, couplers and nuts are usually reused. The number of reuses should be per the manufacturer's and/or specialty Engineer's recommendations. The lifting bars, couplers and nuts should never be reused if they have been over stressed, bent or otherwise abused. The high strength lifting bars should never be welded or exposed to arcing. The bars should be removed prior to performing any welding on the lifting frame.

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Typically lifting holes are positioned through the top slab near the inside or outside of the webs. The holes may be formed using corrugated PT duct pieces, tapered inserts, or other methods may be specified by the Engineer. The exact positioning of these lifting holes is critical. It is important to develop a proper positioning and restraining device that will hold the forms in place during the concreting operations. More than one positioning device might_:!Je needed to accommodate the variations in the lifting hole layout. It is important to develop a quality control procedure to insure that the right layout is used. The bars may be overloaded, the segment may not hang properly or the lifting frame may not fit if these holes are not positioned correctly, or if they move during the concrete pour. The lifting frame is secured to the segment through the formed holes with PT bars (Figure IO.l(a)). The slope and cross fall of the segment can be adjusted by changing the connection points on the lifting frame, by varying the sling length, or by hydraulically adjusting the relative position of the frame and the segment. It is essential the proper stressing requirements of the PT bars is followed when securing the frame

to the segment. The system could be designed to rely on the friction developed between the frame and the segment to insure that the bars are working in tension. If the bars are not stressed properly. the frame could slip and shear the PT bars. After erection of the segments, the lifting holes should to be plugged with an approved non-shrink grout, or as specified by the Engineer. The hole forms used in the casting yard should provide a surface that will insure a proper bond between the plug and the segment, and prevent the plug from falling out.

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Providing access to form, pour, strip and finish the bottom of the holes, especially when they are outside the webs may require the use of rolling platforms, personnel lifts, or other movable platforms. Access inside tall and sloped segments may require the use of sophisticated movable scaffolding to reach the lifting holes locations.

10.1.21nserts Embedded in the Segment Webs and Protruding Above the Top Slab Lifting devices that could be embedded in the web include high strength bars, looped strand bundles, or special inserts. The high strength bar, plate, nut and coupler assemblies are encased in aPT duct. Care must be taken when placing the assemblies to ensure that the bottom nut and upper coupler are fully engaged on the bar.

Because of the lack of visual confirmation, this system poses a risk of accidents if the nuts, couplers and bars are not properly engaged and secured. However, with proper quality control, it has been used successfully on many projects. The lifting bars, couplers and nuts typically cannot be reused because they are embedded in the concrete. High strength lifting bars should never be welded or exposed to arcing. The lifting frame is secured to the embedded PT bars. The slope and cross fall of the segment can be adjusted by changing the connection points on the lifting frame, by varying the sling length, or by hydraulically adjusting the relative position of the frame and the segment. It is essential to follow the proper stressing requirement of the PT bars when securing the frame to

the segment. The system may be designed to rely on the friction developed between the frame and the segment to insure that the bars are working in tension. If the bars are not stressed properly, the frame may slip and shear the PT bars. After the segments are erected, the bars may require trimming to provide adequate concrete cover,

and the PT duct encasing the bars has to be grouted. The bars and couplers should to be protected from damage throughout the project, and could cause tripping hazards when they are protruding above the deck, or recessed in holes. Special precast handling inserts may also be used to lift the segments. When using these inserts it is important to follow the recommendations of the manufacturer.

When looped strand bundles are used to lift the segments, the loop embedment length and details must be properly designed. The top of the loop should be encased in a metallic light weight pipe section and then bent in a U shape. The pipe section is used to make sure that the load is evenly distributed among the strands. The bottom of the loop should be properly secured to the web rebar as detailed on the shop drawings. The strand loops should be properly positioned in the segment and a recess form should be used around each loop penetration. The proper positioning of this recess form may be problematic and hard to maintain during the pour. After erection, the loops are trimmed inside the recess to provide the proper concrete cover. The

recess is then filled with the specified grout or patching material. The recess detail should be analyzed carefully in order to keep the patch from popping out under traffic.


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The exact positioning of any of these inserts is critical. It is important to develop positioning and restraining device that will hold the inserts in place and plumb during the concreting operations. More than one positioning device may be needed to accommodate the variations in the lifting insert layout. A quality control procedure is required to insure that the right layout is used. The inserts may get overloaded, the segment may not hang properly, or the lifting frame may not fit if these inserts are not positioned correctly, or if they move during the concrete pour. The use of embedded rebar to lift the segments is not recommended.

10.1.3 Lifting Slings or C Hook Frame The segments may be lifted without the use oflifting holes or embedded inserts. Lifting slings, flat braided wire rope, or nylon straps (Figure IO.l(b)) may be used to handle the segments.

This method is not suitable for balanced cantilever erection, or in sitmi.tions where the segment must be placed in its final position prior to disconnecting from the erection equipment. Slings are commonly used to lift the segments for precast segmental erection using underslung trusses or falsework. Wood, plastic, or rubber softeners or shoes should be used around the segment edges to prevent any damage to the segment or slings. Another segment handling system that does not require the use oflifting holes or embedded inserts is the C hook lifting frame (Figure IO.l(c)).This lifting frame can get quite heavy when handling large segments and could affect the selection and size of the erection equipment.

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In some situations, a combination of lifting devices might be used on the same segment. The segment could be lifted with a sling in the casting yard and during transport, and then erected with a lifting frame at the erection site. The segment structural integrity should to be verified regardless of which lifting system is used. At least one lifting option that is acceptable to the designer should be shown on the contract drawings. Tiu:nbuck/es or lor control

~celp$

of crosstaJJ

C-Hook

Fl;:~rt

1./(bJ

Pmtectiw shoes and hlirdwood pScks to a wid damsge tq

Adjusting Jatenrl posiUon_ D! frame will ttl/ow segment to hang at required cross/all with 4 $ingle centrAl lift.

corpers When lifting

with slings,

Shim Profiled shim

tilling with a lt'iJme Is pretered and

is often lhe only solution tor erectioJt.

Figure 10.1-Hand/ingSegments

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10.2 Handling and Transporting Precast Segments in Precast Yard 10.2.1 Handling precast segment from the new-cast position to the match-cast position The first time the new segment is handled is when it is being moved from the new-cast position against the bulkhead to the match-cast position. Typically, the main operations affecting the handling are as follow: 1)

2)

3)

4)

5)

6)

The sides and bottoms of the inner core form are loosened up. The concrete should have attained the minimum strength requirements identified in the casting manual before performing this operation. None of the form elements supporting the concrete should be distrubed. The segment should not be exposed to excessive vibration. Typically no post tensioning is required to perform these operations. It is essential that the as-cast survey of both new cast and match cast segments be performed before starting any loosening or stripping activities on the forms. The match-cast segment is broken free from the new-cast segment. The segments should be separated as indicated in the casting manual and in accordance with the recommendations of the form designer. Typically, the soffit table under the match cast segment is tilted slightly as the tables are pushed apart using horizontal hydraulic or mechanical jacks. It is important to keep in mind that the segment separation takes place while the concrete is still relatively green, and the shear keys are especially vulnerable to breakage. The match-cast segment is rolled away on its soffit. Once the segments are separated, the match cast segment is rolled on its table using a winch, a hydraulic system, or a loader. The inner core form is lowered and retracted and the wing forms are lowered. When the concrete has reached the appropriate strength and, if required, the transverse PT is stressed. The transverse PT may be stressed in stages. The form elements supporting the concrete can be removed, the core form is folded and retracted, and the wing forms are lowered. The new-cast is freed from the bulkhead. Depending of the form design, the new cast segment may be separated from the bulkhead using the same method as for the separation ofthe match cast segment. The segments should be handled carefully in order to avoid shear key breakage. The new cast segment is rolled on the soffit form. Once the new cast segment is separated from the bulkhead, it is rolled on its table using a winch, a hydraulic system or a loader. Later, after the rebar cage installation, the new cast segment is rolled again, and is set and adjusted in the match cast position.

10.2.2 Handling and Transporting of Precast Segments From the Casting Area to the Storage Area Depending on the yard set up, point and patch needs, PT requirements, grouting, transverse PT pour backs, and other finishing issues, the segment will be moved to either an intermediate finishing area or directly to the storage area where it will be finished. Before lifting the segment, the concrete should have reached the specified lifting strength and the required transverse PT should be stressed. Storage areas should be properly prepared to prevent any settlement under the segments. Once the segment is connected to the lifting frame or to the slings, it can be moved to the storage yard.

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Commercially available equipment could be used to move the segments from the casting area to the storage area. However, due to the site conditions, yard layout, optimization of the operations

and economics, custom built equipment may be better suited for the project (see Figure 10.2).

Figure 10.2- Straddle Carrier Transporting Segments to Storage, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)

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Figure I 0.3 - Gantry Crane on Rails, Singapore LRT (photo courtesy ofDEAL!Rizzani De Eccher USA)


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The segment lifting frame dimensions and weight should be considered in reference to the capacity of handling equipment. Safety details such as wheels guards equipped with automatic engine kill switches, travel alarms, air horns, proper communication between the operator and the spotters, and other safety devices are essential to the safe operation of the large handling equipment in the narrow runways of the storage area.

Some of the typical methods used to move the segments in the yard are: 1) Cranes with or without tractor/trailers or special carrier Depending on the project needs, the availability of equipments and economics, the segments may be moved using large cranes to either load the segments on tractor/trailers or special carriers, or to crawl with the segment directly into the storage area. This method may be inefficient, but may be used if the storage area layout can accommodate large runways for the travel and swing radii of the cranes and the transporters. 2) Rail Mounted Gantry Cranes (see Figure 10.3) If the yard layout is rectangular and all the segments can be stored on a long and narrow strip of land, a rail mounted gantry crane would be the ideal solution. This type of equipment can operate in very narrow runways and optimizes utilization of the storage area. The rail mounted crane can typically straddle several segments. If electric power is available, this type of gantry could be operated using electric umbilical cords running off the permanent power grid. This solution is usually more economical that equipping the gantries with generators. Rail mounted gantry cranes require special foundations under the rails and should include provision to correct for any ground settlement under the tracks during the life of the project. These gantries require relatively flat terrain. 3) Rubber Tired Straddle Cranes

If the storage area is square or irregular, a rubber tired straddle crane might be needed. These cranes typically straddle one or two segments and will require multiple runways. The runways should be wide enough to allow the safe operation ofthe equipment between the rows of segments.

This equipment is typically capable offour wheel steering and four wheel drive operations. These features are quite helpful when negotiating tight turns in the yard. The tire pressure exerted by the straddle cranes is quite high and requires proper soil preparation. Furthermore, measures should be taken to constantly monitor and dress up the runways. Ignored ruts and depressions will affect the operation of the equipment, and will cause premature wear and tear on the drive and steering mechanisms. Proper drainage throughout the casting yard must be provided to avoid water ponding in the runways. The path and turning radius of straddle cranes must be considered when laying out the casting yard. The straddle crane manufacturer should be made aware of the soil conditions and terrain topography in order to properly size the drive and steering systems.


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The soil conditions in the storage area must be analyzed and proper soil preparation must be provided to minimize any settlement under the weight of the segments. Crane mats or concrete pads may be needed to spread the load. The segments should be stored on hard timber blocks using a three-point support configuration (Figure I 0.4) in order to avoid warping the segment during the storage period. Warping of the segments would cause complications in fit up of the segments during the erection and the fmal geometry of the bridge. Variable depth segments require more complex cribbing due to their sloped bottom soffits, in order to keep the segments vertical and provide proper stability. The storage area should be monitored periodically, especially after heavy rain, to check for any settlement of the segment supports. If a settlement is observed that would jeopardize the stability of the segment, or if the three-point support configuration has been compromised, the segments should be relocated, and the settlement problem should be corrected. Double stacking of the segments is not always permitted, but is possible depending on the design of the segment (See Figure 10.5). It is essential that the designer check the effects oflocalized loadings due to stacking to avoid cracking. Double stacking requires the approval of the Engineer. The segments should be periodically checked for any damage resulting from the double stacking. Barrier rebar projections must be considered when double stacking. Double stacking of severely variable depth segments is not recommended. When double stacking is being considered it is essential to check that the segment handling equipment has the clearance to clear two segments with rebar projections on dunnage, as well as a

segment with a lifting frame and rigging under the hook. Non-synunetrical segments may crack under their own weight, and may require special attention

for storage. Finishing of the segment could be done in the fmishing area or in the storage area. Access should be provided for transverse post-tensioning and grouting, cleaning of the joint faces, point and

patch, secondary pours, and repair of small defects. If secondary pours are needed, it is important to provide runways wide enough to accommodate concrete trucks or other delivery methods.

No repairs should be made on match-cast faces.


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Three point support in storage to prevent warping NOTE: Supports under webs

Figure 10.4- Storing and Stacking ofSegments DOuble_ StnCI{iritJ is Oiiljl .POSSible if allOwed -by spticllkiltions aJli] has

been approved by_ EngJneer

Use 3-point support

Check localized condiUons for structural adequacy

(Engineer)

Periodically monil11r stack~d segments for any evidence of undesirable effects

such 8S cracking stJd lake t;tppropriale action if necessary..

Figure 10.5- Double Stacking ofSegments


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10.3 Transporting Precast Segments from the Precast Yard to the Erection Site Before the segments are transported to the erection site, it is important to verify that all quality control documents are properly completed, and that the segment has been accepted for incorporation in the bridge. As a minimum, the segment should be checked for the following: I) 2) 3) 4) 5)

Proper concrete strength Specified curing duration is met. This duration could vary from 7 days to 6 months. Transverse PT tendons are stressed and grouted per the contract documents. All the patching and repairs are completed and accepted by the quality control inspectors. All permanent and temporary post-tensioning ducts are checked for obstructions, correct layout, and placement.

6) All inserts are checked for correct placement. 7) Proper identification and orientation of the segment. 8) The segment match cast face has been pressure washed or lightly sandblasted. Depending on the site conditions, and the location of the casting yard relative to the erection site, the segments may be transported by water or by land.

10.3.1 Transporting Precast Segments via Water Using Barges When the casting yard location is remote from the project site, or when the bridge is to be erected over water, segment delivery by water should be investigated. This method usually requires double handling of the segments, especially if a portion of the superstructure is over land.

10.3.1.1 Loading If the casting yard does not have access to a navigable waterway, the segments will be transported as described in section 10.3.1.2 to a location with access to a navigable waterway.

If the casting yard has easy access to a navigable waterway, the following items must be considered: I) Any permitting issues that would restrict access to the waterway from that property. 2)

Water depth adjacent to the edge of the project. Dredging permit requirements, and buried utilities in the vicinity of the property shore line.

3)

Abutters issues

4)

Waterway width and the potential for blocking the channel during the loading of segments

5)

If an existing bulkhead is available, it should be checked for structural integrity and fitness. If found deficient, permit requirements to improve the existing bulkhead must be investigated.

6)

Equipment and segments lateral loading of the bulkhead.

7)

New bulkhead design and permitting issues: a. Bulkhead parallel to the shore line: probably easiest to permit, but could block the channel during the loading of the barges. b. Barge loading slip dug out inside the property line. This method could result in a large slip in order to accommodate the barge sizes being used to

transport the segments. c. Loading finger piers protruding in the waterway. Probably the least expensive and most difficult to permit. This method would consist of two rows of piling with runways. Lateral stability and side loading should to be investigated, especially in waterways subject to ice loading.

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If a slip or finger bulkhead type is selected, the barges could be loaded directly with the straddle crane used in the storage yard. If a bulkhead parallel to the waterway is selected, the segments will be delivered to the bulkhead area by the straddle crane and will be loaded on the barge using a crane with enough capacity to reach to the centerline of the barge. This method will require additional sets of segment storage pads and lifting frames at the bulkhead to stage the segments during the transfer from the straddle crane to the loading crane.

10.3.1.2 Transport The barges used for segment transport must be checked by a qualified Engineer or Marine Architect to certifY the integrity and fitness of these barges. Figure 10.6 shows barge transportation of a segment hauler. Another view of segment transport by barge is shown in Figure 10.7. ABS certification may be required. A proper cribbing and tie-down system must be provided to secure the segments during the transport. Variable depth segments require a more complex and adjustable cribbing and tie-down system. The hull of the barge must be checked and strengthened as necessary to accommodate the segment loads. The depth of the waterway, especially outside the navigational charmels, must be checked and cleared of any obstructions. Water depths affected by tides, seasonal variations and prevailing winds, should be evaluated. Freezing rivers and waterways could have a major impact on the segment delivery. The weather forecast should be checked prior to loading and moving the barges. Since barge towing is quite weather dependent, the logistics of transport, on-site mooring and storage should be studied in details. The path of the tugboat and the loaded barges should be checked for overhead obstructions, low clearance bridges, movable bridge schedules and operational reliability, etc ...

10.3.1.3 Unloading When the segments are delivered to the erection site it is necessary to pressure wash the exposed faces, especially the match cast faces and any exposed steel or secondary pour back area in order to wash off the salt spray. If the PT ducts were not properly sealed prior to the trip, they must also be flushed with potable water and dried with oil free compressed air.

If the segments can be delivered within the reach of the erection equipment, they will be unloaded directly from the barge. Depending on the wave action and swells in the area, connecting the lifting frames to the segments could be difficult and might require special attachments to guide, hold and secure the frame to the segment as the lifting bars are being tightened and stressed. Pinch point type injuries and falls are a serious concern during this operation.

Due to the potential of bouncing of the frame on the segment as it is being secured, the proper aligmnent of the winch cables inside the block sheaves should verified prior to lifting the segment off the barge. Proper access and fall protection should provide safe access to reach the top slab inside the box, the top of the segments, and the areas to be pressure washed. If the segments are being stored on barges near the erection site, proper mooring must be provided. Mooring should be properly permitted and designed to withstand the local wind, water flow, waves, and swell conditions.


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Figure 10.6 Barge Transportation of a Segment Hauler

Figure 10.7 Bmxe Transportation of Segments


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In some instances the large barges needed to transport the segments to the project vicinity are too large and deep to get all the way to the erection site. In these situations, the segments could be transferred, at a great expense, to smaller barges or could be unloaded and transferred to a land hauler at a potentially equal or greater expense.

If the segments have to be transferred from the barges to land hauler in order to reach the erection equipment, an unloading/staging area near site must be set up. This area will be set up with either a bulkhead parallel to the shoreline a slip or fmger piers as discussed in theloading section above. Water depth and dredging permits should to be investigated. The bulkhead parallel to the shoreline is the most likely solution at the job site. If a bulkhead is used, the segments will be unloaded with a crane and loaded on a tractor /trailer set up or a special hauler and transported to the erection equipment. The haul road should be designed to accommodate the segment hauler's horse power and turning radiuses. A low profile/rough terrain rubber tire straddle crane can be used to move the segments from the unloading area to the staging area, and later on to the erection equipment.

10.3.2 Transporting Precast Segments Off-site via Land When the casting yard is not at the bridge location, the segments could be transported on land by either tractor/trailer or by special haulers. Figures 10.8 through I 0.11 illustrate movement of segments from the storage yard to the erection gantry for the New Baldwin Bridge in Connecticut. Figure 10.12 shows delivery of an 85 ton diaphragm segment to the Boston Central Artery project.

10.3.2.1 Loading The segments could be loaded on the hauler with the same straddle crane used in the storage yard. Typically a section of the storage yard is designated as the loading area. This section should have easy truck access and gantry crane rail crossing.

10.3.2.2 Transport Several issues should be considered when analyzing the segment transport to the erection site: i) The weight and dimensions of the segments often exceeds the legal load allowed on the local streets and highways. ii) The over-weight or over-dimension permitting procedures vary from one locality to another. iii) The existing bridges in the immediate vicinity of the project, and sometimes the only access to the erection site might be derated and load restricted. iv) The haul route might be crossing overpasses, buried utilities, underground box culverts, etc ... all of which might have different load rating. v)

In some regions, no over-weight permits are issued in the spring due to ground thawing

concerns. No segments, heavy loads or equipment can be moved outside the project limits during this period. vi) Police and special escort vehicle might be required. vii) Some locality with traffic congestion concerns or sensitive abutters may impose additional

restriction on the hauling time. viii) Overhead clearances such as underpasses, power lines, traffic lights, overhead utility lines,

etc ... along the haul route should be checked. The barrier rebar on top of the segments is usually the controlling element. ix) The distance from the casting yard to the erection site and the availability of haulers could require the setting up of a staging area at the erection site.

Depending on the segment load and the permit requirements, multi-axle tractor trailer combination might be used to haul the segments. For extra heavy segments, special selfleveling, all-wheel steering hydraulic haulers can be used. Special tractors, weighted down with massive counterweights for extra traction, are

typically used to pull the special haulers. Some of these special haulers are self propelled, however, they move at very slow speeds and could be restricted from travelling over highways. Under certain conditions and if rail sighting are available at both the casting yard and at the erection site, transporting the segments by rail might be a feasible solution. However, the unreliability of the rail system schedule and the lack of control over the railroad operations make this solution a very risky choice.


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10.3.2.3 Unloading Whenever possible the segments should be delivered directly to the erection equipment. In some instances, double handling the segments and storing them onsite cannot be avoided. If staging areas are used, and if a crane is used to unload the segments, the crane and haulers will be needed again later on to load and transport the segments to the erection equipment. Alternatively, the haulers can be uuloaded with a low profile rough terrain straddle crane that will later on deliver the segments to the erection equipment. If the segments are being delivered on top of the completed spans, the superstructure should be check for the loaded hauler or straddle crane reactions. The haul roads should be designed to accommodate the segment hauler's horse power and turning radiuses. If the segments have to be transferred to a barge, the sarue set up discussed in "transport off site over water" should be considered.

10.3.3 Transporting Precast Segments On-site via Land In addition to the methods available for off site transport, when the casting yard is located iu the close viciuity of the erection site, the segments can be transported to the erection equipment directly by low profile haulers or special mega haulers. Loading, transporting and unloading: when the castiug yard is on site, the sarue equipment could pick up the segment from the storage area, transport it along the bridge alignment and unloaded it at the erection equipment without the assistance of other cranes or equipment. If a low profile rough terrain rubber tire straddle crane is used it should be designed to be able to pick up the segment from the storage area, travel with the segment along the haul roads and over the completed spans and fit under the tail of the overhead gantry to unload the segment. Typically the straddle wheel gage is designed to match the segment web spacing. Alternately the segments could be delivered on the ground under the gantry or withiu reach of the crane or the winch and beam system. If the full span method is used for the casting of the superstructure (entire span is cast in one element), some customized handliug and transportation equipment is necessary. This method of construction is generally used for very long bridges such as high speed rail projects, and major viaducts or bay crossings.

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Figure 10.8- Gant1y Loading Segment on Segment Transport Vehicle, New Baldwin Bridge, Connecticut (photo courtesy ofPerini/Homsi)

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Figure 10.9- Truck and Segment on Trailer, New Baldwin Bridge, Connecticut (photo courtesy of Perini!Homsi)


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Figure 10.10- Delivery of Segment to Launching Gantry, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)

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Figure 10.11- Segment Lifted by Launching Gantry, New Baldwin Bridge, Connecticut (photo courtesy of Perini/Homsi)


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Figure 10.12- Delivery of 85 Ton Diaphragm Segment for the Boston Central Artery Project (Photo courtesy of Unistress Corporation)


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10.4 Erection of Precast Segmental Bridges 10.4.1 Factors for the Selection of Precast Segmental Bridge Erection Methods The main factors that influence the selection of erection methods and equipment discussed below are:

Project schedule and construction duration Superstructure design Access and site conditions Project team Equipment availability

Project Schedule and Construction Duration The project completion date is typically specified in the contract documents. In some instances meeting these completion dates would require accelerated schedules. Accelerated schedules typically require working on multiple fronts and would dictate acquiring specialized and expensive equipment to meet the project milestones. The additional expense associated with the specialized equipment and the acceleration costs can often be justified when the owner offers early completion incentives. On certain projects the construction sequence and traffic phasing might require multiple headings to keep up with the project completion schedule.

.)

Superstructure Design The geometric characteristics of the superstructure including span length, pier height, horizontal curvature, maximum grades and cross slope, and the degree of consistency and repeatability of these characteristics throughout the project have a major impact on the erection methods used. Projects with small segments or very tight radius curves require the use of cranes while large projects with repetitive span layout would favor undersluog trusses or overhead gantries. Short projects with very high piers and heavy segments might require a beam and winch set up to erect the heavy segments. It is important to verify that the superstructure is capable of carrying the additional construction loads introduced by the erection equipments. Ground or barge mounted cranes introduce minimal construction

load into the structure while overhead gantries tends to introduce some of the most significant loads the bridge will ever see during the construction stages. Access and Site Conditions Access and site conditions are probably the most significant factors in determining the most efficient erection method. When working over land, the factors that should be considered range from environmental issues such as wetlands and protected habitats to interferences with local traffic, businesses and railroad crossings. When working over water, the factors that affect the selection process include: Water conditions (depth, flow, ice, etc.) Required permits The feasibility and cost of constructing access trestles Wave action and barge bounce must be taken in consideration when connecting the lifting beams to the segments Salt water splash on the match cast faces and inside the PT ducts must be addressed. Proper design, analysis and certification of transport barges must be performed Loading and unloading facilities must be studied and permitted.


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The availability of suitable real estate in the vicinity of the project site for a casting yard will influence the erection and segment delivery methods. The distance from the precast yard to the bridge site will determine the number of transport vehicles, the need to provide staging areas and double handling or barge docking facilities at the erection site. In case the of a limited storage area where double stacking is being considered, the segments must be checked for that loading condition, and proper dwmage and soil preparation must be performed in order to avoid differential settlement. The route from the precast yard location to the erection site will dictate the size and type of segment that can be transported, especially if the route includes low overhead clearance or weight restrictions. Local ordinances and permit requirements and costs also must be considered when selecting the casting yard location.

The transport route from the casting yard to the erection site must be checked for overhead clearances (power lines and overpasses) and for underground structures (utilities and culverts, etc.). Transport permit requirements vary widely from one location to another and seasonal restrictions may apply. Project Team The experience of the project team, which includes the Owner, Designer, CEI, Contractor's engineer and the Contractor is another major factor that may affect the selection of the erection method. The more experienced the team, especially the Contractor, the more open he will be to considering a sophisticated

erection method if it is deemed to be the most efficient way to construct the project. The availability of skilled labor in the project market is another factor that should be considered during the selection of complex erection methods.

Equipment Availability The availability of erection equipment (cranes or specialized equipment), new or used, the competition among the suppliers and the availability of steel fabricators during the selection process will affect the cost and delivery schedule of the erection equipment, and will influence the selection process. The additional costs associated with the mobilization, assembly and commissioning of new specialized

equipment, and the cost of refurbishing and modifying existing equipment, should not be underestimated as

it is a major component of the cost and time analysis in the selection process. The more expensive specialized equipment will benefit from the economy of scale of larger projects where . the initial investment can be depreciated over a large project.


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-)

10.4.2 Erection Methods for Precast Segmental Bridges The erection methods used for the construction of Precast Segmental bridges discussed in this section are classified according to bridge type as follows:

)

10.4.2.1

Erection Methods for Span-by-Span Type Bridges

10.4.2.1.1

Underslung Trusses with Crane on Ground or Barge Mounted on Water

10.4.2.1.2

Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck

10.4.2.1.3

Erection with an Overhead Gantry

10.4.2.1.4

Full Span Erection with Winches I Strand Jacks

10.4.2.1.5

Full Span Carrier I Erector

10.4.2.1.6

Full Span Erection on Shoring Falsework

10.4.2.2

Erection Methods for Balanced Cantilever Bridges

10.4.2.2.1

Balanced Cantilever Erection by Crane on Ground or on Water

10.4.2.2.2

Balanced Cantilever Erection by Overhead Gantries

10.4.2.2.3

Balanced Cantilever Erection with Beam and Winch/Strand Jacks

10.4.2.2.4

Balanced Cantilever Erection with Special Erectors

10.4.2.3

Erection Methods Conclusion

·. . J Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments

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1 0.4.2.1 Erection Methods for Span-by-Span Type Bridges 10.4.2.1.1 Underslung Trusses with Crane on Ground or Barge Mounted on Water (Figures 10.13 and 10.14)

Figure 10.13- Crane Erection ofSpan-by-Span Bridges on Underslung Trusses (drawing courtesy ofFlatiron Constructors, Inc.) This is a relatively economical solution if ample room when access is available at ground level.

Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Pier bracket installation and relocation Segment delivery Erection crane access and swing radius

Material delivery Support operations Access must be maintained throughout the erection phase. This could be quite costly if working over the water mainly due to trestle and /or barges and tugboat costs. This method is quite dependent on the weather conditions especially when working on the water.

This method is governed by the maintenance of traffic rules when working on land. If working over water, special loading and unloading facilities must be provided. •

The pier brackets supporting the trusses are typically cycled and erected on the leading pier by the erection crane.

,J Chapter 10.0 Procedures for Handling, Transporting and Erecting Segments

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I

Figure 10.14 '-Crane Erection ofSpan-by-Span Bridge on Underslung Trusses (photo courtesy of Flatiron Constructors, Inc.) The relocation of the underslung truss can be accomplished by one of the following methods:

I

Winches and selflaunching oflong trusses: In this method, the long trusses are designed to be self contained and are capable of self launching from pier to pier using winches mounted on the deck or on the trusses. Jacks and grips to push long trusses forward: In this method, the long trusses are designed to be self contained aod are capable of self launching from pier to pier using a hydraulic jacking mechanism mounted to the superstructure and a perforated rail attached to the trusses.

Crane and C hook to relocate short trusses: In this method, the short trusses are fitted with a C hook allowing the trusses to be relocated by cranes from span to span. Crane dragging trusses on pier brackets rollers or on C hook trailers: In this method, long trusses can be relocated from pier to pier using a ground based crane that will partially support the nose end of the trusses while the tail of the trusses are rolling on the pier brackets. The trusses are pulled forward toward the next pier. For short trusses the trusses can be fitted with a C hook attached to trailers on top of the deck. The trusses can be relocated from pier to pier using a ground based crane that will partially support the nose end of the trusses and pull it forward toward the next pier while the rear of the trusses are supported by the C hook on Trailers. This method should be avoided although it is sometimes shown in the contract drawings. Dragging the trusses with cranes is a very

delicate aod risky operation because of the high potential of side loading the crane boom. Combinations of the above The precast yard location and distance from the bridge site has a major impact on the erection operations. If the continuous delivery of segments using a reasonable number of trucks cannot be maintained, the segments will have to be delivered to the site off shift and stored near the erection

site. This operation will result in added cost due to the double handling.


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10.4.2.1.2 Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck (Figure 10.15)

Figure 10.15- Span-by-Span Erection on Underslung Trusses with Crane or Derrick/Lifter on Deck (drawing courtesy ofFlatiron Constructors, Inc.)

)

Access the pier locations must be provided for the following operations: Foundations and substructure construction Pier bracket installation and relocation Access must be maintained throughout the erection phase.

Segment delivery by special carriers or trucks Need to check that the deck can handle the construction loads from the crane and the segment deliveries. Trusses can be relocated using the same methods described above. The Precast yard location and distance from the bridge site has a major impact on the erection

operations. The bridge length and the distance that the segment haulers have to back up on the bridge deck also impact the erection operations. Self-launching of the pier brackets is difficult with underslung trusses so it is likely that separate ground or water based equipment will be required to install and remove the brackets.

···~ Chapter I 0.0 Procedures for Handling, Transporting and Erecting Segments

24 of37

10.4.2.1.3 Span-by Span Erection with an Overhead Gantry (Figures 10.16 and 10.17)

Figure 10.16- Span-by Span Erection with an Overhead Gantry (drawing courtesy of Flatiron Constructors, Inc.) Access to the pier locations must be provided for the foundations and substructure construction.

Depending on the Over Head Gantry (OHG) design, all major segment erection operations could be performed from the OHG and/or the constructed deck. Typically OHGs are more complicated and more expensive than underslung trusses. The segments can be delivered from ground/water level or from behind OHG on the newly erected structure.

In order to speed up the erection operations the segments could be stored under the OHG on the bridge alignment. Span-by-Span erection using and OHG method is typically an efficient solution for light rail applications where the total span weights are relatively low, but it has also been used successfully on highway bridges. Some OHGs are hinged to accommodate tighter radii. The use of an OHG typically provides a greater clearance envelop under the structure Must check for overhead clearances: overpasses, power lines, etc.

This method is also a good solution for the erection of short spans and abutment spans if the OHG is already on site to erect the balance cantilever spans.

During the relocation from pier to pier, OHGs are typically self contained and are self launching. In special situations, the OHG may need the assistance of a crane to relocate some of its supports.

·...


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Figure 10.17 Span-by-Span Overhead Gantry Segment Erection (photo courtesy ofFlatiron Constructors, 1nc.)


26 of37

··~

10.4.2.1.4 Full Span Erection with Winches I Strand Jacks (Figures 10.18 and 10.19)

Figure 10.18Full Span Overhead Erection with Winches (photo courtesy ofFlatiron Constructors, Inc.)

Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Casting or assembly of superstructure Winch assembly, installation and relocation Segment or concrete delivery Construction equipment access

Material delivery Support operations

)

Access must be maintained throughout the superstructure construction phase. This is not a very common construction method.

The superstructure could be PC segments, assembled on the ground under their final position or CIP full span, either cast on the ground under their final position or delivered on barges. This method also requires additional temporary bottom slab PT to carry the span self weight during the lifting

Figure 10.19- Full Span Erection James River Bridges, RI


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10.4.2.1.5 Full Span Carrier I Erector (Figure 10.20)

Figure I 0.20 - Full Span Carrier I Erector (photo courtesy ofDEAL/Rizzani De Becher USA)

)

Access to the pier locations must be provided for the foundations and substructure construction. This type of erection equipment is typically used on light rail projects where the span weights are relatively low. However it has also been used on larger structures. The initial investment in equipment for this method is quite significant. To be economically feasible, this method must be used on very large and repetitive projects where the cost of the equipment can be depreciated over many spans.


28 of37

10.4.2.1.6 Full Span Erection on Shoring Falsework (Figures 10.21 and 10.22)

Figure I0.2I- Full Span Erection on Shoring Falsework (drawing courtesy of Flatiron Constructors, Inc.)

Figure I 0.22- Full Span Erection on Shoring Falsework (photo courtesy ofFlatiron Constructors, Inc.)

)

Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Shoring assembly and relocation Segment delivery Erection crane access and swing radius Material delivery Support operations This method can accommodate very tight radii The use of commercially available scaffolding and cranes minimizes the investment in specialized

equipment; making this method very competitive for small projects It is quite labor intensive: ground preparation, tower bases construction, towers erection, towers

adjustment, towers bracing, header beams installation, jacks installation, dismantling the system after erection and relocation to the next span. This method is also slow relative to SBS erection with either overhead or underslung trusses if only one span offalsework is used. To match the speed of a gantry or truss at least two sets of falsework will be required.

·· ...

)

This system is feasible where the maintenance of traffic is not an issue. A more complex falsework system will be required to erect over traffic or railroads.


29 of37

10.4.2.2

Erection Methods for Balanced Cantilever Bridges

10.4.2.2.1 Balanced Cantilever Erection by Crane on Ground or on Water (Figures 10.23, 10.24 and 10.25)

Figure 10.23 Balanced Cantilever Erection by Crane (drawing courtesy ofFlatiron Constructors, Inc.)

Access along the bridge aligoment must be maintained for the following operations: Foundations and substructure construction Pier bracket installation and relocation (if needed) Segment delivery Erection crane access and swing radius

Material delivery Support operations Access must be maintained throughout the erection phase. This could be quite costly if working over the water mainly due to trestle and /or barges and tugboat costs. This method is quite dependent on the weather conditions especially when working on the water. This method is governed by the maintenance of traffic rules and ground access conditions when working on land. If working over water, special loading and unloading facilities must be provided. Personnel, material delivery and post- tensioning operations are less efficient when working over water

The use of readily available cranes eliminates the investment in specialized equipment making this method the most economical solution for balanced cantilever erection where easy ground access is

available. This method imposes the lightest construction loads on the superstructure. It can accommodate tight radii and steep grades.

The cranes should be sized to erect the pier segments (typically the heaviest) and all other segments.

Typically the crane works from the end of the cantilever. Special attention should be paid to the midspan segments where the crane could get boom bound while erecting from the side of the bridge. By using ground based cranes, the erection can proceed from pier to pier without having to wait for the closure pour and continuity post-tensioning activities. With multiple cranes the erection could proceed simultaneously on several headings.


30 of37

Unlike the specialized erection gantries and trusses, the same cranes can be used to support various activities throughout the project. Furthermore, after the completion of the project these cranes can be readily used on other projects.

Figure 10.24- Balanced Cantilever Erection by Crane (photo courtesy of Flatiron Constructors, Inc.)

Figure 10.25- Balanced Cantilever Erection by Barge Mounted Crane (photo courtesy of Flatiron Constructors, Inc.)


31 of37

10.4.2.2.2

Balanced Cantilever Erection by Overhead Gantries (Figures 10.26, 10.27 and 10.28)

Figure 10.26- Balanced Cantilever Erection by Overhead Gantry (drawing courtesy of Flatiron Constructors, Inc.) Access to the pier locations must be provided for the foundations and substructure construction.

Depending on the Over Head Gantry (OHG) design, all major segment erection operations could be performed from the OHG and/or the constructed deck. These would include: Personnel access to work area Pier brackets erection Pier segment erection Installation of post-tensioning platforms Overhead service cranes Material deliveries Pier access Closure pour forming, pouring, and stripping support Integral fmishing bridges A cost-benefit analysis is needed to determine what options make economic sense. It is a very cost effective method if:

The bridge is long with repetitive spans. Restricted access at ground level Existing gantries are available and require a minimum of modifications. The possibility of reuse of the gantries is much greater if they are properly designed with versatility for future projects in mind. The project alignment including assembly area must be checked for overhead obstructions such as power lines and overpasses. OHG tend to be manufactured overseas. Adequate time should be anticipated for shipping, custom clearances and trucking to the project site. Due to the long lead time on certain components, the major spare parts should be ordered in advance and available on short notice.

Local electricians, hydraulic mechanics and suppliers of metric odds and ends should be identified early on and should be involved in the commissioning of the equipment.


32 of37

)

Assembly and commissioning of the custom made OHGs typically takes much longer and costs more than anticipated. Due to the project layout and the construction sequences, the OHGs may have to be relocated from one aligmnent to another. This relocation often can be accomplished using one of the following methods: Dismantling, trucking, reassembling and re-commissioning

Self launching back and repositioning in the new aligmnent Reconfiguring for reverse operations and re-commissioning

Loading complete OHG on special transporters moving it

) Figure 10.27- Balanced Cantilever Erection by Overhead Gantry (photo courtesy ofPerini/Homsi)

Figure 10.28 -Balanced Cantilever Erection by Overhead Gantry (photo courtesy of Flatiron Constructors, Inc.)


33 of37

10.4.2.2.3

Balanced Cantilever Erection with Beam and Winch/Strand Jacks (Figures 10.29 and 10.30)

Figure 10.29- Balanced Cantilever Erection with Beam and Winch (drawing courtesy of Flatiron Constructors, Inc./Kiewit) Access along the bridge alignment must be maintained for the following operations: Foundations and substructure construction Segment delivery Material delivery Support operations Access must be maintained throughout the erection phase. Each segment must be delivered right under its final position. This could be quite costly if some of the segments are over shallow water or land obstructions. For spans over water this method is quite dependent on the weather and water conditions Special loading and unloading facilities must be provided to transfer the segment on barges and vtce versa. Personnel, material delivery and post- tensioning operations are less efficient than when working with an overhead gantry. By using a winch and beam, the erection can proceed from pier to pier without having to wait for the closure pour and continuity post-tensioning. By increasing the number of winch and beam setups the erection could proceed simultaneously on several headings. A large crane is needed to relocate the winch and beam from pier to pier. A typical assembly could weigh as much as segment.


34 of37

(J

This method can lift very heavy segments very high and can be more economical than an equivalent crane or OHG. A separate operation is needed to either erect precast pier segments or falsework for a cast-in-

place the pier table. The superstructure must be checked for the erection loads caused by the equipment. The equipment design and fabrication lead times and the commissioning duration should be considered carefully when scheduling the project.

)

Figure 10.30-Balanced Cantilever Erection with Beam and Winch San Francisco-Oakland Skyway Bridge (photo courtesy of Kiewit/Flatiron/Manson Joint Venture)


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10.4.2.2.4 Balanced Cantilever Erection with Special Erectors {Figures 10.31 and 10.32)

) !

On certain projects, the typical erection methods discussed above are not well suited for the site conditions. In these situations, special equipment must be developed designed and fabricated. As with any other erection equipment proper review for conformance with the applicable US codes, by a qualified designer, is a necessity. Furthermore these special erection methods tend to be prototypes and as such longer fabrication, commissioning and debugging times should be anticipated.

)

Figure 10.31 -Special Erector (drawing courtesy of Flatiron Constructors, Inc.)

l) Chapter I 0.0 Procedures for Handling, Transporting and Erecting Segments

36 of37

Figure 10.32- Special Erector Used on the Dallas High Five Project, TX (photo courtesy ofDEAL/Rizzani De Becher USA) Safety Using Special Erection Equipment Requires: Properly trained labor force Checklists and procedures Experienced site supervision and construction staff

Experienced construction engineer Inspectors are a 2nd set of eyes Repetitive nature of work causes slacking off which increases the risk of an accident through carelessness.

10.4.2.3 Erection Methods Conclusion Many erection methods available Conditions that might dictate or eliminate certain methods: Design Site conditions Schedule Construction sequence Equipment availability Contractor experience Design to US standard and in conformance with OSHA

·..... )

Design-Build projects and Design-Bid-Build projects, that allow redesign or Value engineering to suit the contractor needs and expertise, lead to optimization, creativity and more competitive bidding.


37 of37

TABLE OF CONTENTS

)

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 11.0 ERECTION DETAILS

)

··. ·-

11.0

Erection Details

3

11.1

Permanent Post-Tensioning

3

11.1.1 Anderson Technology Corporation - Transparent Sheathing

4

11.1.1 Anderson Technology Corporation - Super Corrosion Protective (Supra Strand)

5

11.1.2 AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Multi Plane

6

11.1.2 AVAR Post-Tensioning Systems for Segmental Bridge Construction Single Plane/Flat Anchorage

7

11.1.3 DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental Construction

8

11.1.3 DYWIDAG-Systems International- DYWIDAG Post-Tensioning Systems for Segmental and CIP Construction

9

11.1.4 Freyssinet Post-Tensioning Systems- Freyssinet Post-Tensioning Hardware for Segmental Bridges/G-Range Post-Tensioning Systems

10

11.1.4 Freyssinet Post-Tensioning Systems- Freyssinet F-Range PostTensioning Systems

11

11.1.5 Mexpressa- Jacks and Pumping Units

12

11.1.5 Mexpressa - Anchorages and Couplers

13

11.1.6 SDI Post-Tensioning Systems and Services

14

11.1.6 SDI Type C Multistrand Anchorageffype C4.6 Multistrand Anchorage/ Type D Multistrand Anchorage

15

11.1.7 VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type ECiffype ESffype E/PT-Pius Duct System

16

11.1.7 VSL Segmental Bridge Post-Tensioning Systems- Anchorage VSL Type SANS LAB+® System

17

11.1.8 Williams Form Engineering Corporation -The Williams System

18

11.1.8 Williams Form Engineering Corporation -150 KSI All-Thread Bar

19

11.2

Temporary Post-Tensioning

20

11.3

Post-Tensioning Safety Issues

23

11.4

Lifting Segments for Erection

30

11.5

Temporary Supports

31

11.6

Midspan Closure

32

11.7

Construction Schedule and Sequence

33

) Chapter 11.0- Erection Details

I of34

TABLE OF FIGURES CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-5UPPORTED BRIDGES CHAPTER 11.0 ERECTION DETAILS

Figure 11.1

Use of Temporary Post-Tensioning for Erection

21

Figure 11.2

Use of Continuously Coupled Post-Tensioning Bars

21

Figure 11.3

Coupled Post-Tensioning Bars (Continued)

22

Figure 11.4

Anchor Head Hole Pattern

25

Figure 11.5

Jack Alignment with Tendon

26

Figure 11.6

Support of Stressing Ram

27

Figure 11.7

Stressing Personnel Located Away from the Stressing Ram

28

Figure 11.8

Stressing Personnel Safety Harness

28

Figure 11.9

Coupling of High-strength Bars

29

Figure 11.10

Erection Systems: Setting of a Pier Segment and Start of Cantilever

31

Figure 11.11

Erection Systems: Means of Stabilizing Cantilever

32

Figure 11.12

Aligning Cantilevers for Midspan Closure

33

Figure 11.13

Effect of Construction Sequence

34

Chapter 11.0 - Erection Details

2 of34

11.0 Erection Details 11.1

Permanent Post-Tensioning Permanent post-tensioning tendons are installed and stressed as erection of segments proceeds. Both internal and external tendons are used. Internal tendons are located in ducts inside the concrete slabs and webs. They are conunonly used in case of balanced cantilever erection. External tendons are located in polyethylene sheathing which is placed in the interior space of the box girder. External tendons are attached to the structure at the pier diaphragms and at deviation blocks. Comprehensive information on post-tensioning technology is presented in Chapter 3 ~ "PostTensioning Duct and Tendon Installation" of the FHWA "Post-Tensioning Tendon Installation and Grouting Manual" presented in Section II of this Handbook. As an addendum to Section II of the Handbook, information on safety during stressing operations, alternative procedures for calibration of jacks and gauges, and temporary tendon corrosion protection is presented below, and in Section 11.3. Safety PoSt-tensioning stressing operations create very high forces in the tendons and surrounding concrete. Therefore, precautions must be taken to prevent personal injury or damage to the structure. Prior to starting stressing operations, inspect anchorages and surrounding concrete.

Clear the work area of debris to allow for unobstructed movement of the stressing crew. Read and understand all operating and safety instructions for the stressing equipment before stressing tendons. Make sure that all safety stickers applied to the equipment are intact, legible and understood by the stressing crew. Comprehensive discussion of safety issues related to stressing of post-tensioning tendons is presented in Section 11.3. Calibration The FHWA Post-Tensioning Tendon Installation and Grouting Manual requires that all calibrations be performed with specific service gauges and a master gauge as a system. Gauges are often damaged on the job sites as a result of impact or shock, and often two service gauges do

not last the normal six-month period between recalibrations. Recalibration of jacking systems is time consuming and expensive, but can be avoided if the service and master gauges are calibrated

at a dead weight indicator to read true pressure. The dead weight indicator must be calibrated and traceable through the National Bureau of Standards. The contractor should seek approval from the engineer prior to beginning stressing operations to use dead weight-indicated gauges in order to

replace damaged gauges without having to recalibrate the ram and gauges as a system. Temporary Tendon Corrosion Protection Temporary corrosion protection is required for tendons that must be left ungrouted for extended periods due to cold weather or other circumstances. Vapor Phase Inhibitor Powder (VPI Powder) was used for this purpose for many years, but use of this product was abandoned due to health hazard concerns. Currently, corrosion inhibiting oils are being used for temporary corrosion

protection which have detrimental effects on bond. Recently, VpCI Powder has been developed which is non-toxic and biodegradeable. Use ofVpCI Powder is reconunended in preference to corrosion inhibiting oils. Product and material safety data on VpCI Powder may be obtained from: Cortec Corporation, 4119 White Bear Parkway, St. Paul, MN 55110 Toll Free (800) 4-CORTEC, Phone (651) 429-1100, Fax (651) 429-I I22 Email: [email protected], Internet http://www.CortecVpCI.com

)

Details on post-tensioning systems available for use in segmental bridge construction in the United States are presented in Sections 11.1.1 through I 1.1. 8.

Chapter 11.0 ~Erection Details

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11.1.1 Anderson Technology Corporation

SUPPl..ll=ROF AN[)ERSQf\1 POST-'TEN$10NING SY$TEM Anderson 1"Eictlnology Com()ra~i. . -. -. . ott (AT<'~) wJIS co-falli)de.J by Dr. Artb\lt.R.Andecion,a !'ioneerof •'

'

prtlstreSSciicorii:rell> iri.North .Anl!!i:iCa. 'Ilie Andemon PrlS!'tTensil>riing.Systeni (APS)has evolved win the otijlinal Amei:iC311 syswmto in.clpdeay~ ofi1Tmat¢o:i"':andm¢thadodeveloped ato~nd.theP;>eific Rlm.

~Transparent· sheathing for.ciHi:niai tendons inside box jtirSj>eCtion bOth. dutilig and i~r !lroutili~ can be done bj virtue of the liniL~Y (85%) oftbe sh.,thirig. which is <:OIDPO.Sed <>fElhylene B~e
deviator makes/it possi~!e tpr ~e leijdon jo bl> in Tablet.

Jriint

/-1\

''

"

\'

1J

t

} >

\;

¥I

,.\I { '·'{I!

'1 I

:0" <

lJ

tt

~·

:1

j

f !

f

I

\r

\1

/

Fig.-1. Dauble Cased Anchorfi>r Clear Duel Tendon

Table. I.

No. ofOB'Strands.

Dianleter

TranspPnmt Sheathing (mm) UnitMass(kg/m)

O.D.

I.D.

12

88.3

79.9

l.lJO

19

l!O;S

100.7

1.45

21

1362

126.1

1.90

Head· Office : Onarimon Ynsen Bldg. 2F

3·23-5 Nishi-Shinbashi Minato-kuTokyo, I 05-0003 JAPAN Phone: +81·3·3437-1999

Fax: +81·3-3437-9581

Unit.Length.

9m (Straight)

USA Office: Old Brolin Place Anderson Island, WA98303 Phone: 253·606-6097 Fa.x : 253·884-5683

:.) Chapter 11.0- Erection Details

4 of34

... ··~

Anderson Technology Corporation (Continued)

11.1.1

Fig-2 .~bows on~ Qf .b)jdges !!Ddet s~eptal. CQDSlrUction .!n J~pan'.USliig 100% exte1!1altend\»ls 1o1>e l'rt>tedted'by g.:.,tit lilfed !ntra!\Sp..;.,;nt Si!<\l!IQJngs. Transparent slt<\lllhliigssllow~ in F!g,-3 are install¢(! inSide a2-room box glrderhaving 3 corrugate
we)ls. l'ig.4 sllQ:ws llo\v'fu:int•oftM.high'visco!lSit.Y gro:ut.

*Super Corrosion PJ'
)

APS; A modified adh~ive resin ba.sed on. hign dens,ity p<>lyethyl~!'· fills !he. inn.er spaces among wires wilh0 ut eausing ilhra\'elling' imd coatS !he outer wires•. The natura of the resin and the injection method are such as to elimh\ale pinholes. Ordirtliry wedgesican be usedt(ulti•Str&ld"teJ]donf<:>r slay• cables, as 115ed in !he ex!r;i-dose bridge io Japan sbQwnin Figure7.

Fig-5

Supro!Sub unbonded Strand

Fig.~6

Supro Multi-SJrand-Tendon (Prefabricated)

Fig...-7

Mijiakodagawa-I1ridge

* These twO materials ·are intemationaUy patented. Chapter 11.0- Erection Details

5 of34

11.1.2

AVAR

Post-Tensioning Systems for Segmental Bridge Construction

• Systems_ available for tendons ranging from 4 to 3].(1.6" $irands

• Foim Travelers •- Installation Labor •- Value Engineering Smart~~ ~'hg'daDOT

C!:rnra:lot:Pt:CCMCnn~ Pwt-te~aildform T~tljAVAA

forfc'min. 6,500-Psi

Single Plat1e (SPS)

dffnensions·In inChes

NO~ of

Anchorage strands 0.6"Q SPS 12.6 12 SPS 19.6 19 SPS22.6 22 SPS27.6 27 SPS31.6 31 SPS 37.6 37

eA

B

11 112 141/2 151/2 17 18 20

17 17 17 20 22 24

eC

D

o_o_

E

oF

71/4

3318 4 4118 4318 4718 5112

31/4

13 15 17 18

8114 9 95/8 10-518 11112

41/4 4112 43/4 51/4 5314

20 22

G

NxP

#4

5tums@4 5tums@4

"#4 #4

5tums@l4

#5 #5 116

5tums®4 6tums@3 6turns-@3

Edge Dist. Anchor • Spacing

9 10 11 11 12 13

16 18 20 21 23 25

" based upon 2:' cover

r 0: si _L_

forfcmin. 4,500 psi

Multi Plane (MP & MPR}

No. of

dimensions are inches

oc

D

o_o_

9x9

7

09 e11

20 26

6 7318 B 1/4

3 33/8 4

3 3112 41/4

A

0.6"0

MP9.6 MPR 12.6 MPR 19.6

9 12 19

E

B

Anchorage Strands

oF

G

10

#4

111/4 14"112

#5

#5

NxP

Slums

2 2 7tums@2 6tums

.

Edge Disl Anchor Spacing 7 7 3(4 9112

11 121/2

15112

" based upon 2H cover

AVAR Construction Systems, Inc. 504 F Vandell Way, Campbell, CA 95008 (408) 370-2100 Fax (480) 370-2329 [email protected] Chapter 11.0 - Erection Details

6 of34

11.1.2

A\f/iD

Post-Tensioning Systems for Segmental Bridge Construction

;r,::.;;r-..;;:.o;;.

for fc min 4 500 psl

Single Plane (SP) No. of Ancllorege stiands

dimensions in Ind:les

A1

N2

B

.c

D

E O.D.

13.314 17114 171/4• 19114 20112

13314 161/4 161/4 19114 20112

16 20 19 20 20

73/8 81/4 9 10

33/8 4 41/8 4314 5

3112 4114 4112 5 5114

0.6~~

SP12.6 SPW.S SP22.6 SP27.6 SP31.6

'12 19 22 27 31

10518

Edge Anchor Pistarice Spacing 9 1.1 11 12 13

14112 18 18 20 21

""based up_on _2..- cover

Flat Anchorage (FS & FM)

No. of Anchorage Strands

tor f.., min. 4,500 psi

A1

A2

B

G

D

E O.D.

45/8 33/8

6 91/8

21/8

2112 15/8

2 2

0~6'"0

FS4.6

4

10112

FM4.6

4

9518

d1mens10ns 1n mehes as an option, 1"'x3" flat duct may be used

Q~"' Lj}I t!IJ3 FS Anchorage

~

( @@0@@)

'--' FM Anchorage

All listed systems use 0.6'" diameter strand per ASTM A 416, 270 ksi l_ow relaxation

The above AVAR systems are currenUy or have earlier been installed on the following segmental bridyes: Rosecrans and Kramer Bridges in Los Angeles. CA, Big I in Albuquerque, NM ~ Spaghetti Bowl in Las Vegas, NV Oyster Point, So San Francisco, CA- Benicia-Martinez Bridge in Benicia, CA- New Bay Bridge Skyway Structure in Oakland , CA- Richmond-San Rafael Bridge, CA- Smart Highway Bridge, VA- Los Angeles-River Bridge, CA Riverside Bridge, Mount Vernon, WA


7 of34

11.1.3

DVWIDAG-SYSTEMS INTERNATIONAL DYVII!D"l.> l'osHenSicnlog ~ems for S!'!!mental Conslr!l¢ion'and tliP (;Qilsfrcu~l!on' The 1)'{\yjO~-M:~~lPO&t~T~·:·~--is·shown -for hooded apptleationstiW_ may~~tl¥1:friri)$li.".a$'~-~ t~~

-~gvwioAG,MU~~fraM:_E¢i-frats&nrnfr~em--~-9$··~-(),~--tl~~~-~a'!li:lS.

Avallabk! 1\ilcnorage Type,; /'l,ltiltlslramt 'r~dQn'TYJMr~... ,(tiS-~em)

Nurrib!l! outs ~dS

,1)~-

"""'*""'~ 1)1><' ~~~,,.;.'[ Pfate·~_e--$0'

~J!~:~~·i?F~

Loop Anchor..ga Hv

fiif;Aii~~~F/;.;-· __

)\h:::

os,

00

5}7

Oil

00

:12.

.

1S' ''!:!·

27

~

•

•

Permanent Grout Caps _maqe_ frtnri Nylon AeinfQt.ced PlaStic - Meels FOOT spebs

::n

•·-

• •

:·-:_:e::···

C!xrP!er ~li DSt Syste.rt.-100

I

1!4,

•

..il ::.•

I

l!Wpectioo:arid grout port tor Anehots, .acCessib!e frorri tM i9P- M~.s FQOT Specs_

OYWIDAG-SYSTEMS INTERNATlONAL-USA INC. Phooe: +1·S30-7 3911 00

E-mail: [email protected]

wWw.dsianierica.eom

Chapter 11.0 -Erection Details

8 of34

11.1.3

DYWIDAG-SYSTEMS INTERNATIONAL

"fOOT~P~

Multistrand System 100.

Flat system 100

\

Top_Viaw·

Ooct1)

Pla.Slidlut<{ 1}

0

SldeViaw

Top GJout and lnspection Port


9 of34

11.1.4

FREYSSINET Post-Tensioning Systems

D

FREYSSINET 44880 Falcon Place, Suite 105 Sterling, VA 20166 (703) 378-2500 FAX: (703) 378-2700 [email protected]

FREYSSINET Post-Tensioning Hardware for Segmental Bridges FREYSSINET C•Range Post-Tensioning Systems The Ftey'sSinet CRilnge ·anchorlige Is:.lhe most _Compact posHehsi6niti!:_ .system avail
nCIS anchorage

rriost often ·used for-priiTiarY longitudunal, transverse diaphragm and vertical

Groul Cap {optiomU}

tendonsc The family of Freyssinet CRange Anthorages have been sUccessfully tested in acordanee with the AASHTO Specifications for Special Anchorage Devices.

Versatility The -system is designed for a wide range of applications with the same anchorage t)pe: Accomodares aU internationally avaiJable sizes and grades of 15mm strand (15.2 and 15.7

mm), including galvanized and unbonded strand; Applicable for- internal and external post-tensioning tendons: o Bonded o removable o removable and adjus!able o removable, adjustable and detensionable.

Compactness

Size 3Cl5

4CI5 7C15 _9Cl5 12CI5 !3C!S I9CI5 22C15 25CI5 25CI5P 27Cl5 31CI5 37Cl5 55CI5

A 150 150 180 225 240

250 300 330 360 350 350 385 420 510

B 110 120 150 185 200 210 250 275

300 290 290 320 350 420

c 120 125 186 260

D 85 95

346

110 150 150 160 185 220 230 220 120 230

466

255

516

300

165

246 256 430 400 360 360

H 50 50 55 55

65 70 80 90 95 95 100 105 110 145

~I

~2

40

"50

45 60 65 80 80 95

105 110 110 115

65 70 85 85 100 110 115

120

115 120 125

130 160

135 165

These very compact ar~chorages provjde efficient transfer of the prestressing forces into the concrete, fucilitating more economical designs by: reducing web thicknesses in beams and box girders, reduced blister-and rib dimensioru; allowing for a greater concentratiOn Ofanchorages and pre-stress force at the anchorage zones; reducing post~tensi~ming anchor blocks dimensions thereby minimizing strand deviations.

Chapter 11.0- Erection Details

10 of34

11.1.4

FREYSSINET Post-Tensioning Systems FREYSSINET 44880 Falcon Place, Suite 105 Sterling, VA 20166 (703) 378-2500 FAX : (703) 378-2700 [email protected]

D

Lightweight Jacking Equipment Lightweight, comp_fi,Ct and automaQc c..Range jacks: proyide:_ reduced _pre:stresssing anchorage recesse-s_ thanks. to ·the: compact Strarulpilit_em-and jack nOSes'; redUced offset distiffices_ to -,vall$ with Silla1fer .imposed moments; resulti~ in a.reouction insuppleiDentalrefuforcement and.improved . cOnciete platerirent; etihimced constructability, such as Dandling,, stressing and end ancbotag'e corrosion protection.

JCJ5 4C!5 1C:!f

9Cl_5

HCJ5

13CI.i

19Cl5

21Cl5

J!CI5

FreyssinCt-C-Range rif Anchorages

)

FREYSSINET F-Range Post-Ten$ioning Systems The Freyssinet F-Rai:lge· system was designed fattransverse deck slab post-te_nsiOning appliCations with tendon sizes rnnging from 1 to 5 _strands. The anchorn. are generally used with flat duct, and are· tensioned either strand-by-strand ·with monostrand equipment or as a-single operntion wJth multi-strnndjat:ks.

The F-Range supports increased productivity by enabling tensionirig in a single step using multistrand jack vs. strand-by-stmnd -using a monostrand jaCk. Pre-seating of non-stressing ends is easily act:omplished thereby eliminating expensive anchorage recesses. The F-Range offers a complete mnge of flat, low profile anchors suitable for transverse deck posttensioning of se~tal bridges and other thin elements such as building slabs and beams.


II of34

11.1.5

JACKS Two finesofhigh perfonnanet! lll!d durability DEL jacks exist for lhe stressing of strand cables, with or withom automatic gripping an!! release, ofadequate weight and size for their function and lhe size and length ofcables;

T J~tcks Equipadwilh automatic. frontgrippinglrelcasingand wedge sealing devices, they perfonn a streSSing/wedge operatiiJD.in less than l 0 minutes and ~strand tails of0.3..meters only for nonnal tendonsizes. They are the recommended option for short tendonsand precise streSSing openitions_, induding_wedg.e s_eating lo~ c~:mtrol. SeaU{)ss is Jimite4 at-3 m~ ..

The ligbteS!, easiest to handle and maintain multistrandjacks. They feature rear band operated gripping and semi-automatic releasing. Seat loss. is limited at 10 mm. .

PUMPING UNITS

DEL Multistrand Pumping Units include all the hydraulic control devices for!he opern(ion. Theybave been ergonomically designed for heavy duty and low maintenance. Electrical or gas power, optionally. T Pumps Three circuit, fur Stressing, Relnlction and Wedge Seating, they feature.2 ganges for superior control. Used with T jacks. E Pumps Two circuit, for Stressing and Retraction. They work at mid-high oil pressure for.lowest maintenance, in accordance with their corresponding E jacks. GROUTING MACHINES The tnixture of cement. water and admixtures must be done under a strid--Ihixing time and velocity control and must not coutain lumps nor any air bubbles during injection into the ducts.

DEL grouting machines include the mixing and injecting opern(ion in a single piece of equipmen~

easily handled, with pressures of up to 25 bar, without the presence of air bubbles, using any type of cements and admixtures.

Av. Nativitas 429 * 16090 Xocbimilco. D.F. *Mexico* Phone +(52)(55) 5615 7561 *Fax 5676 66'20 Email mexpresa®mtxpresa.eom * www.mexpresa.com


12 of34

11.1.5

ANCHORAGES AS Active, Standard A~tive or Stressing anchorages are-those located anhe-str:essiilg -ends· Oftendons, DEL AS anchorages-are suppliedinChtding-wedges, lVedge & bearing plates,trailsition and:g'rout port. Grout caps, whether-and as-required..

Design may_ ~pe_cifY active anchor3_ges.·on both ends· of aPT tendon evewthollgh stressing is-carried o~t_at one_ only,..For wedge seating 19S!' recup,era~ioih__sliiJ,nS: ·can:_he:-plaeetl be_twee_n wedge plate and-be_aringpJate, thrm,gll-a lift-iJJf.

AR Active, Adjustable for:- t~nsion-adjUstment aftedock-..off.

They~ supplied

completeaS·fOi-:AS type;

including adjusting_nut

)

AE Active for External. Post-tensioning Adjustable-and easy to instaU Clild remove, DEL AE anchorages have.been speciallydeveloped to withstand_ the dynamic m::tions·oc_~rring at the, en¢; of'externaltendons~ and to epsure a correct grQUting·or filling.ofprotectlon _pipes. They are-supplied complete with wedges, ·threaded wedge plate & nut~ ·capsule, bearing_plate~-fofiil tube~ s.trand:concentrator and grout vent. Where adjusting is notrequired, shiins: are provided instead .ofnut.

AF Active for Flat tendons They are typically used in bridge slabs, when concrete cover is a· must for corrosion protection. Stressing is done strand by strand with standard Mono~trand_ Jacks. Available in sizes up to 4 strands, t11ey are suppHed with ·wedges, wedge/bearing plate, transition and grout port. Pocket formers and grout caps, whether and as require_Q.

COUPLERS Ffixed Used for prestressed concrete elements' post-tensiOned_ c_onnec_tion. Also called_ Continuity Anchorages, they are supplied complete with_ standard bearing plate & coupler body, swage heads, strand concentrator,- shell and grout ports.

trumpe~

,.,_ M Mobile

For muJtistrand cable extension. Used mostly in repair jobs _for big sjze cables. They are supplied complete with strand _concentrators & deviators, single couplers, sheU and grout ports.

) Chapter I I .0- Erection Details

13 of34

11.1.6 Post Tensioning Systems

The SDl MultiSlraod SJ'Ste:m is the firSt all-hew port~k:nsion· 5Dl PoSt-Tens:iOn'iilg hardwai:e has--b'een-prolren thrOugh th-e.

ing system to be inlro-duced irf over a detade. The syStEm rigofOUs i
''ias desigr.affrom the ground-up- to--a:ddr
concr-ete mixes and the need for Compact

Developed in collabon.tlon vnth AVAA Construdiur.

-,anchora·ges in structural dements vlith mngtosted relnfo!'cing Systems, Inc. of Campbe!l, California, a total of 21 _n~w SOl

st-eel. The S)'S'\Sll is_ eUE:rtsivet· ~«d andapprvr.J, ;md ir;cor-

ancho~ge S'jStems have been sclected and
for use

porates mrnerous teclmi!:al .advances that -simplifY field place. on the new San Francisco·Oakland Bay Bridge Skyway

rne;;t;. mes;ing: ami grouting.

Structures, the

n~'f

Martinez-Benicia Bridge ln California:.

SOl furnishes comprehensive hardware solutions fur and the Sakhalin Offshore Oil Platform currently under conpost·te'nshming- projects warldW'ide, indudmg a broad range strudioh ncar Vladivostok. Russfu. SDI •.vas awarded theof ;;nchor heads ;:fld bearing p!a_tes for 1 to 37 o.G:.inch diamt~ndons,

post-tensioning suppty contracts ftr these thr~e major ~ngi·

all P-ins, duct. hydraulic equlpment

neering structures, tcitilling ovH 40 million po;mds ilf mate-

grouting equipment and fittings. Cninbined wi1h SOl'S serv-

rials. for the San ftancisco-O.akl3:nd Bay Bridge SkjW=f

ic-es for design :;_nd supply of t.:mporary ~reGion structures:,

Structures. SDI also designed and fumtshecl the SE'If

eter slrand

the new post-tensioning system pcoMes a prac"Jc;l ;md ful~: l_;;ur;ching Erection De>
o:; the

superstrm:wr~-

',J Chapter 11.0- Erection Details

14 of34

11.1.6 SDI Post-Tensioning Systems

s

6

)

i!!IJ SCHWAGER IIIIIIDAVIS INC

.. j

FOR MORE lNfOP.MATlON VISIT

198 HJttSO;\tE AYENVE

'SCHW.... GE"?. DAVJS lNC ONlJNE AT

St..n josE, CAI.lfORNlA 95136

WWWSCHWACHt:oAYIS.CQM

T£LEFHONf: 4<08-2lh-9JOO

I


15 of34

11.1.7 Segmental Bridge Post-Tensioning Systems 7455-T New Ridge Rd Hanover, MD 21076 888-489-2687 www.vsl.net

Anchorage VSL Type ECI

Anchorage VSL Type ES

Anchorage VSL Type E

PT-PLUS™ Duct System

Visitwww.vsl.net for updated technical data and dimensions

Chapter I I .0- Erection Details

16 of34

11.1.7 Segmental Bridge Post-Tensioning Systems 7455-T New Ridge Rd Hanover, MD 21076 888-489-2687 www.vsl.net

Anchorage VSL.Type.SA·

)

VSLAB+® System

[

__.__

ANCHORAGE!

.

TENDON SIZES

0.5"

DUCT SYSTEMS

0.6"

PT-PLUsn~

GALVANIZED METAL

EXTERNAL

VSLAB+®

2

-

X

SA

4. 5

4

X

X

1to55

1 to 55

X

X

X

x

x

x

X

X

X

E

• ES

..

12,19,31,43,55 7, 1219, 22, 31, 37

ECI

-

7, 12, 19!22, 31

Visit www.vsl.net for updated technical data and dimensions


17 of34

11.1.8 Williams Form Engineering Corporation 8165 Graphic Drive, N.E., Belmont, Ml49306-9448 (616) 866-0815 http:l/www.williamsform.com

Tll~WilliaJ;n$ Syst~m . .Williams Pre,stre.ssing 1 Post.Tensiorling systems :consist ofhi!l~ ten siTe steel bars aVailable in liVe dilJmeters from ·1" (46 min) to 2-112" (65 11Jill) with guaranteed tensile strenglhs.lo 718 kips {3460 kN). They are P(OVided withi:old.rolledlhreadsoverallora portion ofthe bar's length. All tension components for the·~ystems a.re designed fo develop .100$ of the bar strength. All components of the. systems are d~signed and m~nufactl[red in the United States. Williams All-Thread-Bar systems have been field proven around theworfd.

Grand Rapids, Ml 49504 Phone: (616) 365>.9220

FllJ(; (616) 365-2668 Email: williams@Y!illiamsf91111·~m )Neb: www.wi!lialllsfo[rn.com

Applications

.

·.· .

. . .· . .. , .

.·

Williams All-Thread-Bars were developed for use as Pre'S!reilsi!lg 6ars, Over !he yeats many other applications have heen adoptedsuch as: .. . . •!'lie Test Anchors · • ~oek An~hofl! -,.- ~O~Ctete: Tie·s •,Hanger Bolts • Jacks • Shear Pins

• Transverse Post Tensioning ,long~
Chapter I I. 0 - Erection Details

• Pre-stressed Block. and Brick Construction • Seisrnlc (earthquake) RastrainerSys!ems • Wood Structure Post-Tension Bars • Temporary High Strength Connections • Tower Base Plate Anchor Bplts • High Strength Concrete Reinforcement Bars • Multiple Corrosion Protection Anchors

18 of34

11.1.8 Williams Form Engineering Corporation

•

8165 Graphic Drive, N.E., Belmont, Ml 49306·9448 (616) 866-0815

.

'

http://www.williamsform.com

exceed

· 'Eifediva c:cis:s secliooal areas shown are as. required lrj ASTht A 7.22-98. Achlal iueas rray_ theSe' valutis~ •~ ACf355.1R m:vcnJ.U1 imitates ail U!limall:i.streog!b.ln Shear has a rofll}e:d:.a b) .7-ofifie l&ti~Da!.l t;;i;sie ~---De:si¢1iB safelyfactillsfclsafesbear~based-Oillhe~ofuie. -_ --,_'-- ·- '

""'ro p<~ -

•:~~:::.:T~==d~==~~ihi!~Steei· )

• The ~l«td !hoti!d not'e~ 70% oilhe specified rniniroom let~sie- &tl'ef'lgfh(lf~~sleel • The rnaxim.tm ieslbad should no_t exooeo 00% oflhe spedOOd iTWiimJm mi'ls&f stmlgth·orlhe prestrnSng·steet

Properties

Threads

All-Thread-Bars are ccld threaded to close to~ erances under continuous- monitOrinQ J>.i'o~d~re~ for quality control. Threads ior Wlliinl)S 150 ~SI Bar are specially designed with a r'ugg~,!ljread pitcll wide enough to be fast ~na~d&J5.site'conditions and easy to £1ssemblei Theystellets easily meet the allov.
or .

__ /

\


19 of34

11.2 Temporary Post-Tensioning With most forms of precast segmental construction, it is common practice to use temporary posttensioning to secure the erected segment or segments before the main longitudinal post-tensioning is installed (Figure 11.1). The purpose is: (a) To provide a rapid means of transferring the weight of the segment from the lifting equipment to the structure within the allowable setting time called "open time" of the epoxy jointing material. (b) To allow a fairly even stress to be applied over the whole joint face in order to bed down the epoxy and let it set under uniform conditions. It is normal to provide 30-50 psi average compression for this purpose. If the compression is significantly non-uniform from top to bottom. especially in cantilever construction, then the epoxy joint thickness tends to vary, which, after several segments, can affect the desired alignment. (c) In some cases temporary post-tensioning bars are used to control a temporary stress condition in the structure. For this case, the bars can only be removed after construction has reached a stage at which the stress condition no longer exists. If this is necessary because of some design feature of the bridge, the amount of temporary post-tensioning and its sequence of installation and removal are shown on the contract plans. If, on the other hand, the temporary post-tensioning is required to control a stress arising specifically from the contractor's elected method of operation, equipment, construction loads, or his own sequence of erection, then clearly the temporary post-tensioning should be designed by the contractor and approved by the engineer within the shop drawing process. In any event, the sequence of installation, stressing and removal of the temporary post-tensioning should be clearly shown on the shop

drawings and/or erection manual. Temporary post-tensioning bars may be overlapped so that individual bars or coupled bars extend only a few segments or they might be continuously coupled throughout a cantilever or span. With continuous coupling, it is advisable to evaluate in advance the likely cumulative effect of bar extension and concrete shortening, as the point of coupling can "drift" significantly and eat into tolerances of the space within the blockouts (Figures 11.2 and 11.3). It is normal practice to limit the stress in temporary post-tensioning bars to fifty percent of the breaking strength of the bars. This will allow many re-uses of the bars and the anchors. Sometimes, however, it is necessary to exceed this figure, and, if so, then these bars should not be re-used without the express permission of the post-tensioning bar manufacturer. Visual inspection of bars prior to reuse is always required. If there is any doubt, it is safer not to re-use the bars. In case bars are permanent or cannot be removed for re-use, it is acceptable to stress the bars up to seventy percent of the guaranteed ultimate tensile strength.

When using couplers with post-tensioning bars, it is critical that the couplers are properly engaged on each bar before stressing. Bars being coupled should be marked one half the coupler length from the end of each bar and the bars engaged to the mark prior to stressing. Insufficient engagement of the coupler could result in failure of the connection during or after stressing and possible damage or injury.

In cantilever construction, the temporary bars are only normally needed for the last two or three segments of the cantilever since permanent tendons are installed for most segments. Occasionally, when using continuously coupled bars, it may not be possible to retrieve them after the closure has been made at the midspan. In this case, it is advantageous to plan the temporary post-tensioning so that most of the bars can be recovered prior to adding the last cantilever segment. Temporary bars and particularly their anchors and couplers are expensive, so maximum reuse is desirable.


20 of34

,_···)··.. ·.. _

. r. bars (external}

Temp. P. r. bars may be external fo· concrel_e and anchored on blisters or may be internal through duels with anchors in

P.r. bars (internal)

l

re-formed recesses

Tension 71op Tempocarv

·c_onstruction

stresses for cantile-ver

Bottom

r--; P. "r.

_ .

Camp. M/S +

bars........-, Compression r

~

M=Moment due to loads (Dead load + Construction load) S=Section modulus P=Force of post- tensioning A =-Area of sec-tion e= Eccentricity of Tension post-tensioning + Pe/S = Approx. uniform

J 8

P/A

compression on epoxy joint

Figure 11.1- Use of Temporary Post-Tensioning for Erection

) Elastic shortening of concrete from !!11 P. T.

--Jt-'-

Direction of erection

______::ii~~~,....JL::.__\1-_i_l!___\:-~ e

c

,?::=3 • When using continuously coupled P. T. bars make sure there is adequate clearance (c) for movement of couplers caused by combined elastic effects

Anchor lift-off due to combination of concrete s/Jortening and extension of P.r. bars (e)

I

---=:r=: An alternative to a

recess would .be lo uSe o larger diotne·ter· duc-t in order t-o clear coupler

)

Figure 11.2- Use of Continuously Coupled Post-Tensioning Bars


21 of34

--lrFinal join l

I

-·'

position-(SI)..., FmnJ ela.sflcs:lwrtening at first joint at completion _of

cantilever

(SII)>O

(SI)

r

I

(L)bar

_n:----

JniUal

JOint r - position

-L

-

1--

--~c

':I

Oireor.fum o/ ercrtJon

Points to beware of. wllen using continuously coupled P X bars: 1. Each bar wi.IJ extend a small amount-{typica/Jy 3/8"-1/2" per lOll. segment). so if tlJe position ol tlJe couplers is critical, bars s.l!ouJd be ordered short of £> segment length by this. amount, (0) also:2

Particularly in a cantilever. the cumulative effect of adding more segments and P.1: tendons. causes an increasing shortening of the eal'lier segments, (S) 1'his can be significant and JYil/ effectively make tbe point of coupling of bars in later sepments drift in the direction of erection-eating into any tolerance (C). To avoid or minimize loss of tolerance by these effects tile !Jars. should be ordered to a length shorter than segment length l>y=(S~SI/2}.

3. But-always allow for variation i.'l segment Jengll1s., also. i.e. provide ample tolerance!

Figure 11.3- Coupled Post-Tensioning Bars (Continued)

·.~ Chapter 11.0- Erection Details

22 of34

11.3 Post-Tensioning Safety Issues 11.3.1 Introduction A 0.6" diameter strand is stressed to a force of23 ton, the equivalent of a truck load of steel. Such a force can be dangerous to jack-operators or on-looking personnel if proper precautions are not taken. Posttensioning work should only be carried out by people who have the expertise in this field and operators who are trained under the direct supervision of competent PTI certified instructors. When potential hazards are understood and carefully considered, and combined with preventive measures, the occurrence of workrelated injuries can be prevented. In this chapter safety issues in handling and stressing of post-tensioning tendons are described.

Read all safety and operating instructions and warnings before starting any work or operation. NEVER stand or allow anyone to stand directly behind, above or below a jack when stressing operations are under way.

)

11.3.2. Handling of Post-Tensioning Materials I.

2.

When cutting the steel bands that bind the tendon coils, remember that the coils are under pressure and will want to open up and uncoil like a spring when the bands are released. Strand coils (packs) must always be contained in a proper dispensing unit prior to cutting the bands. Use extreme care when pulling the loose strand end out of the pack center as the spring force induced from coiling tends to push the strand out of the pack. The cut ends of the strands/bars can be extremely sharp and care should be exercised when handling tendons. Deburr ends of the strand/bar.

3.

Do not weld or burn near post-tensioning materials to prevent sparks or hot slag from

4. 5.

Do not use any part of strand/bar as a ground connection for welding. Avoid using a torch to cut the stressed strand/bar. Use an abrasive saw, shear or plasma cutter. It is not recommended to re-use temporary PT bars stressed to more than 60% of guaranteed

touching any portion of the strand or bar which will be under stress.

6.

ultimate tensile strength (GUTS). Usage is typically limited to 20 times. Check internal threads of nuts and couplers before stressing.


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11.3.3 Stressing Jack Calibration Requirements All stressing jacks to be used at job site must have correct and current calibrations. Gauges should be independently calibrated. Generally, specifications require that the jack and the gauge be calibrated as a unit. Do not interchange them. Make sure the gauge being used is labeled and corresponds to the jack. Most specifications require that a master gage be sent with post-tensioning equipment. The master gage is used to verif'y accuracy of the service gage. In some cases, specifications allow the use of the master gage in lieu of recalibration of the jacks and gages as a unit.

11.3.4 Check List for the Jack I. 2. 3. 4.

5.

Prior to use, visually inspect the jack for signs of oil leakage or damage. Prior to use, check and read all safety instructions and stickers. Any stickers that are not intact must be replaced prior to anyone using the jacks. Free cycle the jack for operation, check and bleed air. All air must be purged from the jack or seals may be damaged. Some twisting of the pulling head can occur during shipping or handling. Be sure that internal jack parts are aligned. The jack cannot be installed unless all tubes are in line. If a center hole ram is used the check no 4 will not be needed. Jacks arrive with reusable pulling wedges in good condition. Consult equipment supplier regarding scheduled change, replacement or maintenance.

11.3.5 Jack Safety Instructions

2.

Observe all relevant OSHA standards e.g. use of protective clothing and devices, grounding of electrical equipment, control of work area, etc. All system components must be in good working condition prior to use. Inspect daily for signs of wear or damage. Do not use if grippers are worn excessively, hoses are cracked, pressure gauge is in operable, or other defects are observed.

3.

After inspection, test run system (see operating instructions) to insure all components are in

I.

4. 5. 6. 7.

proper working order. Make sure that the jack is in the fully closed position when moving from tendon to tendon. Do not activate pump while moving the jack. Proper lifting equipment for jack must be available prior to commencing. Lift equipment by lifting harness only. Never use hydraulic lines for moving, or adjusting of equipment. Do not attempt to service the equipment beyond that described in the operating instructions. All other servicing should be referred to qualified supplier's service personnel. Proper and complete connection of the hydraulic lines is vital to the safe operation of the equipment. Improper or incomplete coupling of hydraulic hoses may cause injury or death to personnel, or severe damage to equipment. Check occasionally to ensure that the quick couplers are closed.


..:J 24 of34

11.3.6 Jack Maintenance Requirements All equipment should be properly maintained and equipped with manufacturer-recommended safety devices. Disabling or removing safety devices is dangerous and should be avoided. All unsafe or inoperable equipment should be marked as such to prevent further use of the equipment. Post-tensioning operation involves high stresses and proper care is vital. All workers should be trained and tested by the manager or superintendent before operating any equipment. Knowledge ofthe hazards associated with specific equipment is the first line of defense against injmy.

11.3.7 Installing Stressing Jack I.

Install pattern plate on tendon and slide to anchor head, secure outer strands and then slide back. This assures strands are in correct holes. Misalignment of strands will cause damage to jack and tendon during stressing.

2.

Check alignment of anchor head hole-pattern (Figure 11.4) with that of jack. Confirm second stressing end is also aligned.

)

WEDGE

JACK FRONT

Figure 11.4- Anchor Head Hold Pattern 3.

Install dead-end keeper plate if required. This may eliminate the need for a man watching the dead-end during stressing, and keeps the anchor plate wedges and strand tight.

4.

Be sure the jack piston is in the full return position. In this position, the automatic stressing head tube will be protruding and the wedges will be open. Lift jack and align axis of jack with that of the tendons, slide jack over the strands to anchor head. Jack support must contact the wedge plate surface before stressing begins.

) Chapter ll.O -Erection Details

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0000000

CORRECT

INCORRECT

Figure 11.5- Jack Alignment with Tendon

11.3.8 Secure Stressing Area I.

2.

Appropriate warning signs should be clearly displayed. Warning signal (i.e. horn) shall be used to alert personnel in area that stressing operations are active. People not involved with this work should keep clear and follow any safety instructions from competent operators. Safety Rails I Barricades shall be present to prevent other personnel from entering an area where stressing operations are going on.

11.3.9 Communications It is extremely important to establish proper communication among the stressing crew, especially, when simultaneous stressing operation takes place. Proper communication devices (i.e. radios) shall be present for communication among stressing crew.

11.3.1 0 Access with Stressing Jacks within the Box Detailing the segmental box girder access dimensions, should accommodate access for stressing jacks. Providing adequate and safe access to the work area is vital.


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)

11.3.11 Precaution in Stressing Operation: I. 2. 3. 4. 5. 6. 7.

8. 9.

Refer to safety and operation instructions before operating any jacks. Stressing operations must be under the direct control of a superintendent experienced in such operations. Operators must wear proper personal protective equipment (hard hats, safety glasses and steel toes shoes, gloves and long sleeves, etc.) while operating equipment. Stressing unit should be securely tethered to the structure at all times. In the event a tendon breaks during the stressing operation, the tether will prevent the unit from falling. Operating personnel must keep feet from becoming entangled in the hydraulic hoses while stressing. Cleaning of the wedge cavity is critical to the success of the stressing operation. Cement paste or other debris can prevent the wedges from seating and the strand to slip back. When re-stressing a detensioned tendon, remember to use a new set of wedges. Always discard the old wedges. No one should be allowed to stand behind, directly above, or below the jack when stressing operations are under way. Stay clear of any un-grouted stressed tendons.

11.3.12 Chain Falls to Hold Jack on Stands or on Stressing Platform Always tie off both the pump and the jack when stressing tendons on an elevated deck

Figure 11.6- Support ofStressing Ram

) Chapter 11.0 - Erection Details

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11.3.13 Stay clear of the jack On should keep in mind that the forces are ahnost as high at the fixed-end anchorage as they are at the stressing-end. Always stay clear of the jack.

Figure II. 7- Stressing Personnel Located Away from the Stressing Ram

11.3.14 Do Not Overstress the Tendon Do not exceed the estimated jacking pressure. Overstressing to achieve required elongations is absolutely unacceptable under any circumstances.

11.3.15_Fall Hazard The number-one leading cause of construction-related injuries and fatalities is attributed to falls from height. In work areas with unprotected sides where employee could fall six feet or more, wear safety harness and connect to lanyards with deceleration device. Personnel should be tied off 100% of the time that they are subject to fall hazard.

Figure II.8- Stressing Personnel Safety Harness


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11.3.16 Coupling of High Strength Bar It is crucial that extra precaution is taken while coupling the bars. Bar ends should be marked with half of

the coupler length (Figure 11.9). The end of the bars should be engaged in the coupler up to mark. Bar supplier should instruct about the minimum engagement. If enough thread is not engaged in the coupler, the bar will fail when stressed. Bar Coupler

Min Engagement 0.5L- 0.5"

L

Min Engagement 0.5L- 0.5" · - - - -

Figure 11.9- Coupling ofHigh-Strength Bars

)

-~) Chapter 11.0- Erection Details

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11.4 Lifting Segments for Erection The method oflifting and handling of segments is clearly the contractor's choice, subject to the approval of the owner's engineer.

When erecting a cantilever, it is necessary to lift the segments in such a way that they hang precisely in the position ofthe previously erected segment in order to align the shear keys and temporary post-tensioning bars during the epoxy jointing process. If the position of the two segments does not match, the segment will bear temporarily only on a few keys, which might lead to cracks when jointing. It is quite easy to align the segments if two lifting points (i.e., beam and winch) are used, one over each web. With a single central lift, it is necessary to lift slightly off center so that the segment hangs at the required crossfall. This can be done by using a lifting frame with laterally slotted holes for the attachment of the slings (Figure 7 .l (a)). In any case, the lifting device used for erection must have the means to adjust the position of the segments. Lifting segments at a present crossfall is not necessary when they are to be placed on an erection truss as with span-by-span construction.


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11.5 Temporary Supports Construction in balanced cantilever begins by placing the pier segment on the pier. Setting this segment at the correct vertical and horizontal alignment is critical as any errors are magnified in the cantilever (see Chapter 13 -Geometry Control). It is furthermore essential to support the pier segment in such a way that successive segments can be added. One method of doing this is shown in Figure 11.10. Vertical post-tensioning bars and shim packs are used to stress the segment down to the piers and provide temporary support. (Note the provision of local reinforcement above and beneath the packs to control any possible "bursting" effects). A support system as shown is only suitable for the first few segments, at most two on each side of the piers. Beyond this, the out-ofbalance effects are likely to exceed the capacity of the concrete and of the available bars which can be fitted into the restricted space. After the first few segments, stability shonld be provided by some other means. Temporary towers as shown in Figure 1l.ll(a) can be used either "wrapped around" the pier, with support provided to both sides of the cantilever through the system ofhydraulic jacks, or by a tower on one side of the pier only. With the latter system, the cantilever should always be kept out of balance in the same direction so that the tower is always loaded. Another method of providing stability is through an overhead launching gantry. Figure 11.11 (b) shows how the cantilever is suspended from the gantry. The hanger bars are repositioned to be always next to the last erected segment. With these systems (towers and gantries) control can be exercised over the amount of rotation of the cantilever. This is advantageous when it comes to aligning cantilevers for midspan closures.

)

,-

P. T. bars stressed lo 50%

1

L--~.rPier segment Profiled packs

secured by snug ligllt ltorizonla/ P.r. bars Sleeve

/.____(_aJ_ _I---~

~

Pot bearing

This type of connection is O.K for up to one or two segments- each side of pier only unless specHied or designed otherwise.- Physical limits of bars control.

Alternati.ve anchorages:

.

(a) Dead end plate & nut: wrap with tape to a 1/o w

bar to be screwed oul afterwards. {b) Embedded P. T. bar with coupler.

P T. =.Post-tensioning

.. )

Figure 11.10 -Erection Systems: Setting ofa Pier Segment and Start of Cantilever


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I

/ I

I Jacks

wit IJ

locking · deviceS-/

..-7r:

-

J

I ~ Out

of lmli1ncc

by ienrpontr.v Useful fot

l 'ilrt·ied

l owcrs

rut -ved or

slaighl brtclges IVU!t

Unbalance

n1oderaLe spa.ns erected from ground or Wit'ler.

G~1-11l1J'

Unbalance

n

Ou L o-r IJllla uce <.'a t-ried lhrougb liturger bars of overhead gantry. .Usefull

with gantry construction, for rela lively slraigltt, large spa-ns.

Figure 11.11 -Erection Systems: Means ofStabilizing Cantilever

11.6 Midspan Closure In order to make a midspan closure, it is necessary to secure the new cantilever to the rest of the bridge. This is readily accomplished through "strong backs" stressed by post-tensioning bars to the segments (see Figure 11.6). Strong backs should be carefully checked for the loads likely to be carried. Apart from the weight of the closure joint concrete, this can be some ofthe remaining out-of-balance forces and any force needed to pull the cantilever tip up to level. In addition, the strong backs should be capable of overcoming the bearing friction on the adjacent pier(s) so that the cantilever can follow daily temperature movements after connection to the structure.

Usually the midspan closure is a nominal two- to five-foot gap. Sometimes, however, it can be larger, and might be as long as a segment. In such cases, the added weight of concrete can cause a deflection and rotation at the closure. For the precast segments, this effect is compensated for in the casting curve. The cast-in-place joint itself requires careful placement of the concrete working from one end of the segment to the other to avoid any tendency to "crack" or open up at the bottom of the joints between the segments and the cast-in-place concrete. If the anticipated deflection or rotation is likely to be very large, such as with a very large closure, then consideration should be given to casting the bottom slab first and applying a nominal posttensioning force (say, 100 kips) through it prior to completing the rest of the pour. This will help to avoid cracks in the joints. The weight of the frrst cast-in-place joint connecting two cantilevers causes an unbalance which is usually controlled by the stability tower (Figure 11.12). This tower will deflect under the effects of the additional load. This deflection will lower the elevation at the cantilever end where the cast-in-place splice is poured. The arnonnt of this deflection should be carefully predetermined and compensated for. Cantilever tips also move because of the effect of sun radiation on the deck. The effect of temperature effects on the casting of midspan splices is described in Section 13.9.2.


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\_)

_,/ /

/

H Steel beam "Strong Backs·

~~

'

-Midspan closure device Connected to deck witll p I. bars . --New can!J/el'er /

•' '• •' ,, Stability tower .. bars Lllrougb lifting holes PT

7

//

b

I

P. T =Post-tensioning

Figure 11.12 -Aligning Cantilevers for Midspan Closure

11.7 Construction Schedule and Sequence The casting curve will reflect the various deformations the bridge will have if constructed in accordance with the schedule and sequence the contractor proposes. The construction schedule and sequence are important. In fact, so important that once sequence and schedule are selected as a basis for the casting curve, a change of sequence or schedule or both may require a change of the casting curve and possibly even a design change. The schedule is important because once cast and under stress, concrete has the tendency to deform (i.e., !-beams which camber up as soon as the prestressing is applied). If the camber is checked again after a period of time, say a month, it has often increased, and, as time goes by, will increase even more. This increase in camber is caused by concrete creep. In segmental bridges where spans can be longer, this creep effect may amount to several inches. In order to compensate for these creep effects, they are calculated based on the contractor's construction schedule. The construction sequence is also very important. First, the sequence details when certain spans will be built. In addition, the sequence indicates when continuity post-tensioning will be applied. This is the post-tensioning provided in the span to connect two adjacent cantilevers. The continuity post-tensioning has the tendency to camber the span in which it is stressed, but will deflect the adjacent cantilever end. These deflections are carefully compensated for in the casting curve. Ifthe sequence was changed so that the continuity post-tensioning in the span with the deflecting cantilever were stressed first, the span would go up instead of down, and the compensation would be wrong. An example ofthis is given in Figures 11.13(a) and (b), where different sequences are used to construct the same bridge requiring completely different compensation of deflections caused by continuity post-tensioning.

·..

) Chapter I I .0- Erection Details

33 of34

The bridge deflections are generally calculated by the contractor's specialty engineer and reviewed by the DOT or a consultant. The reason is clear. Only the contractor, after making out his schedule, can know for snre when and how the structure will be constructed. Exceptions to this rule occur, for example, when the designer decides to prescribe the sequence, and has determined from his calculations that the effect of the schedule is minor (in case of short spans). During the design process (pre-bid), the designer must analyze this structure for compliance with specifications based on the construction sequence clearly shown on the contract drawings. During construction, the contractor or the contractor's specialty engineer will calculate deflections based on the anticipated construction schedule.

.4

II

A 11

'h!

'2'

[:;;:::==;===11(1===;;:::==;]1 A A A A

c·

D

'i

k ; .:::J 11 C::

v·

I~ :

A:

:A

A A

A

c

F

A

II

A

A

A

II

A A

A

t :: 4 == = =-= Ls: -= j e· gc-.:::::::;A;::::===:=;n;::::=---:Jg

A

ri~;:==:;=======;====;JI LA A 21 11

i'

:;:3 II C::: :~

'k'

II

Three-span structure showing mid-span and tailspan splices

B. Erec:l cantilevers C. Close tailspan splice and post- tensioning /). Deflection caused by ''C'" above E. ComperJsation of de!JectioJJs by ··c'" above F. Completed structure

c·.

Close mid-span splice MJd posltension mid-span D'. Deflection caused bv "c'" a/mve E' Compensation of de.flel'lions by

"c"" a/Jove

F'

Completed structure

[a)

(b)

Figure 11.13- Effect of Construction Sequence


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)

TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 12.0 EPOXY JOINTING, DUCT COUPLER DEVICES, AND PREPACKAGED GROUT

Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout Purposes of Epoxy Types and Application of Epoxy Duct Coupler Devices FREYSSINET Post-Tensioning Systems VSL Segmental Duct Coupler General Technologies, Inc. Precast Segmental Duct and Duct Coupler Prepackaged Grout BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction 12.4.1 BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction 12.4.2 SIKA Corporation Epoxy Resin for Segmental Bridge Construction 12.4.3 SIKA Corporation Prepackaged Grouts for Segmental Bridge Construction

12.0 12.1 12.2 12.3 12.3.1 12.3.2 12.3.3 12.4 12.4.1

3 3 3 6 7 8 9

10 13 14 15 16

)

Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout

I of 16

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 12.0 EPOXY JOINTING, DUCT COUPLER DEVICES, AND PREPACKAGED GROUT

Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure

12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.1 Oa 12.1 Ob

Mixing Segmental Bridge Epoxy Applying Epoxy Onto Face Of Segments Epoxy Squeeze Out After Stressing Of Segments Epoxy Resin Being Applied To Precast Bridge Pier Segments Multilevel Corrosion Protection for Bonded Post-Tensioning Tendons Completely Filled Duct with Prepackaged Grout Prepackaged Epoxy Grout Poured Into Anchorage Zone Applying Sikadur 31, SBA On Central Artery Bridge In Boston, MA Sikagrout 300 Pt Being Used In Segmental Bridge Construction Post-Tensioned Strand Terminus Sikadur 42, Grout-Pak Pt Mixed In Pail

3 4 5 6 11 11 12 15 16 16 16

)


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12.0 Epoxy Jointing, Duct Coupler Devices, and Prepackaged Grout 12.1

Purposes of Epoxy The purposes of using an epoxy resin in the joint between the segments are: • • • • •

12.2

To maintain the strnctnral integrity of the joint and maintain a monolithic concrete segment To completely fill any minor surface imperfections and irregularities between the match cast surfaces To provide a water and grout tight seal, preventing chloride intrusion To act as a lubricant when erecting the segments To ensure a tight fit between the segments so that the compressive and shear stresses are transmitted directly across the joint

Types and Application of Epoxy Epoxies are formulated as two-part compounds consisting of a resin and hardener. When mixed together, they begin curing which can take anywhere from a few minutes to a few hours, depending on the formulation, the ambient and storage temperatnres, and the mass of the epoxy. The cure time will be shorter when epoxies are mixed in higher temperature conditions and in larger masses. For some applications, such as in span-by-span erection, it is desirable to have a long pot life to allow for the erection and stressing of a complete span, which may take several hours. Details on the commercially available epoxies for use in segmental bridges are presented in Sections 12.4.1 and 12.4.2.

Figure 12.1- Mixing segmental bridge epoxy


3 ofl6

Segmental bridge epoxies are specially formulated as either normal or slow setting resins. For segment-by-segment erection, the normal set epoxies are typically used and for span-by-span erection, the slow set epoxies are typically used. In addition, they are formulated for use in different temperature ranges, from 20'F to 115'F. It is important to use the correct pot life and correct temperature range to ensure adequate working time and proper strength gain of the epoxy. Prior to application, the joint surfaces must be clean and sound. They may be dry or damp, but

free of standing water or frost. It is important to remove dust, laitance, grease, oils, curing compounds, impregnations, waxes, foreign particles, disintegrated materials and any other contaminants before applying epoxy. Mixing of the epoxy is typically done in the pails. The pre-proportioned units allow for all of Part A (base resin) to be mixed with all of Part B (hardener). The units should never be hatched down on site. The epoxy should be mixed for a minimum of3 minutes with a low-speed (400-600 rpm) rotary drill fitted with an appropriate mixing paddle. The sides of the pail should be scraped down during mixing to ensure there are no streaks of unmixed epoxy in the container. When fully mixed a uniform gray color should be achieved. Application requirements are stated in the specifications. Application is typically done by hand, using protective, disposable rubber gloves. Since the application time may be short, sufficient labor should be available to coat the joint in the time allowed. The epoxy should be applied to both faces of the segments to a thickness of approximately 1116 in. on each face. This is sufficient to lubricate the segments and ensure against joint leakage in the completed structure.

Figure 12.2- Applying epoxy onto face ofsegments


4 of 16

When the segments are brought together and stressed, excess epoxy is squeezed out. For joints over traffic, procedures must be implemented to avoid dropping epoxy on automobiles. The epoxy should be left approximately I in. clear around any ducts and approximately Y, in. shy of the outside edges. Once the segments have been joined and stressed, all excess epoxy should be cleaned. Leaving it to harden may make it more difficult to remove later on. It is essential to swab all the ducts before the epoxy cures so that any epoxy squeezed into them does not create an obstruction for the tendons. The use of duct coupler devices simplifies the placement of the epoxy and ensures that the epoxy will not be squeezed into the duct when the segments are stressed.

Figure 12.3- Epoxy squeeze out after stressing of segments

When bridge piers are constructed with pre-cast concrete boxes, epoxy should also be used between the segments for the same reasons described above. The only difference in application is the epoxy is applied in a horizontal and overhead orientation, rather than in a vertical orientation as on the spans (see Figure 12.4).


5 of 16

Figure 12.4- Epoxy resin being applied to precast bridge pier segments

Details on commercially available epoxies are presented in Sections 12.4.1 and 12.4.2.

12.3

Duct and Duct Coupler Devices Duct coupler devices insure the watertightness of the duct across the joint between segments, and

eliminate the problems related to squeezing epoxy into the joint. These devices also eliminate the need to swab out ducts after the segments have been pre-stressed together. Details on three commercially available duct coupler devices are presented in Sections 12.3.1, 12.3.2 and 12.3.3. Plastic duct is also shown in Sectionl2.3.2.


6 ofl6

12.3.1 FREYSSINET Post-Tensioning Systems Freyssinet LLC, 14221A Willard Road, Suite 400,ChantiUy, VA 20151, Tel: (703) 378-2500 Fax:(703) 378-2700 Email: [email protected]

FREYSSINET Post-Tensioning Hardware for Segmental Bridges LIASEAL Coupler System: Leak-Tight Connections for Internal Tendons at Precast Segmental Joints Freys:finet's"LlASEAL coupler is an engineered system. providing leak-tight internal post-tensjoning duct connections across match-cast precast concrete segment joints. LIASEAL is composed ofthn::e clcmen!S: two identical inserts incorporated in the segment faces with a eenlral sealing element-SCreloved into one insert and mechanically engaged into the other insert. The LlASEAL System 1.vas first implemented on the Ringling Causeway Bridge (SR789) in Florida.

Advantages of LIASEAL: •

l..eak-tight connections prevent ingress of segment epoxy during segmental erection and the ingress ofe>.1emnl aggressive agents (wat;:r, chlorides, etc.) over the service life of the structure.

Leak tight connections prevent cement grout leakage and crossovers during grout injection. LIASEAL components are non-metallic, cannot corrode and offer permanent protection to internal tendon prestressing slecl at segmental bridge joints. •

LIASEAL can be used with HDPEIHDPE ducts to provide a complete leak"'tight plastic encapsulation of the tendons.

)

Mechanical engagement

Scre\\ing

Chapter 12.0- Epoxy Jointing. Duct and Duct Coupler Devices, and Prepackaged Grout

7 of 16

12.3.2 VSL Segmental Duct Coupler

Segmental Duct Coupler 7455-T New Ridge Rd., Hanover, MD 21076- 888-489-2687 www.vsl.net

Design Features: •

Complete encapsulation of post-tensioning tendons through segment joints

•

Small form factor- does not require increased duct spacing

•

Tendons can pass through bulkheads at an angle, resulting in reduced friction

Casting Features: •

Uses conventional inflatable mandrel to support duct

•

Duct does not need to be precisely cut to length

•

Uses standard bulkhead

Bulkhead

Inflatable Mandrel

Coupler Sleeve

j

~

Seals

Erection Features: •

No components projecting from segments during segment erection

•

Segment shimming does not impact coupler performance

Visit www.vsl.net for updated technical data and dimensions Patent Pending


...

8 of 16

)·.

.

12.3.3 General Technologies, Inc.

Precast Segmental Duct and Duct Coupler 13022 Trinity Drive, Stafford, TX 77477 888-255-0440 www.gti-usa.net

New GTI Precast Segmental Duct Coupler

)

GT14 Strand Fully Encapsulated Bonded System

Full Line of Round and Flat Plastic Duct 21mm Grou! Fube

Zero Vofd'/f' -

Monostrond Encapsv/alian w/ Me/a/ Ring

Zerov~

Ccp

Zero vOk::fl?Ccp

Zero Void® Bonded Mono-strand System

Chapter 12.0- Epoxy Jointing, Ductand Duct Coupler Devices, and Prepackaged Grout

9 ofl6

12.4

Prepackaged Grout Prepackaged grouts were developed to reduce or eliminate bleed water voids in the ducts, and to achieve complete filling of the duct with a cementitious grout. Prepackaged grouts are recommended for use on all segmental bridge projects. Even when prepackaged grouts are used, it is necessary to inspect all anchorage areas for bleed water voids within 24 to 48 hours after grouting, until the inspection agency is assured that there are no bleed water voids. Subsequent spot inspections of one or more anchorage per span may be conducted provided no voids are found. Any voids discovered must be filled immediately with cementitious grout, preferably by vacuum grouting.

The cement grout injected into a post-tensioning duct is often the last line of defense against corrosion of the steel tendon. Inspection of the tendons is often difficult, and therefore severe corrosion may go undetected for a long period oftime before failure occurs. The steel tendons are susceptible to corrosion damage because of the high steel stress and the small wire diameter, and if allowed to corrode, there is a danger of structural distress. This underscores the need for the use of quality prepackaged cement grout during the construction of the post-tensioned structures.

Prior to the use of prepackaged grouts, site blended grouts were typically used in post-tensioned applications. The biggest problem with the site blended grouts was the bleed water that would form in the ducts. This bleed water migrates towards the upper end of the duct where it accumulates, and is subsequently absorbed into the matrix. This in turn leaves large voids within the duct containing the cable, and this makes the cable more vulnerable to deleterious chemical attack and/or corrosion. In addition, bleed water itself, and deleterious chemicals that are sometimes admixed, migrate with the bleed water and accelerate strand corrosion. For these reasons, site blended grouts are not recommended for use on segmental bridges.

Post-tensioning techniques There are two types of post-tensioning methods: unbonded and bonded (grouted). An unbonded tendon is one in which the prestressing steel is not actually bonded to the duc1fconcrete that surrounds it except at the anchorage points. In this form of post-tensioning, the tendon (seven-

wire stand) is simply coated with a corrosion inhibiting grease and encased in a plastic protective sheath. In bonded systems, two or more seven-wire strands are installed in steel or plastic ducts in the concrete. The strands are stressed and anchored at a connnon site. After the tendons are

stressed surrounding duct is filled with a prepackaged cement grout that provides corrosion protection to the strands. As seen in Figure 12.5, bonded post-tensioning offers multiple layers of corrosion protection to the steel tendon. Protective measures include surface treatment of the concrete, the concrete itself, the duct, the grout, and possibly, strand or bar coating such as epoxy or galvanizing.

In order for the grout to provide protection to the steel, it should form a good bond between the duct and the steel. A grout having good bond characteristics, transmits forces from the concrete


10 of 16

.)

Figure 12.5- Multilevel Corrosion Protection for Bonded Post-Tensioning Tendons to the steel over its length, and thereby relieves load stress fluctuations at specific sites. As a result of site-specific load stress fluctuations, grout sections having poor bond characteristics

)

may crack easily thereby creating easy access for the ingress of moisture and deleterious chemicals such as deicing salts. The grout functions to provide corrosion protection by passivating the steel strands due to its high alkalinity, which in turn is provided by the hydration of potassium, sodium and calcium ions in the Portland cement. Complete filling of the ducts with a non-bleed grout ensures that there is no damage due to freezing and expansion of trapped water/moisture, which in turn prevents damage to the external concrete. This can only be consistently achieved with the use of prepackaged grouts having been formulated to have zero bleed. High permeability resistant characteristics of the prepackaged grout ensure that no deleterious chemicals (deicing Cr) have easy access to the encased steel. Chloride ions destroy the passivating iron-oxide layer on the steel surface, which in turn exacerbates steel corrosion. In addition, carbon dioxide from the atroosphere, if allowed to penetrate through the cement grout, could reduce the pH and thereby could lead to loss of passivity, and ultimately, corrosion. Therefore, it is important that the prepackaged grout have a low permeability .

Figure 12.6- Completely filled duct with prepackaged grout Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout

II ofl6

Prepackaged Epoxy Grouts for Anchorage Zones Prepackaged epoxy grouts are designed to seal and protect the anchorages of post-tensioned tendons on segmental bridges. This is the area that is the most critical for post-tensioned bridges since it is completely exposed to the elements. If site batched cementitious grouts are used for the "pourbacks," they can shrink and crack over time, allowing moisture and chlorides to gain direct access to the steel strands, and over time, initiate the corrosion process. Prepackaged epoxy grouts offer the following benefits: • •

Pre-measured kits (no mixing errors) High bond strength

•

Non-shrink

• • •

Low exotherm Impermeable to moisture, chlorides and chemicals Resistant to impact, vibration and stress

) Figure 12. 7- Prepackaged epoxy grout poured into anchorage zone

Details on commercially available, prepackaged grouts are presented in Sections 12.4.1 and 12.4.2


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12.4.1 BASF Construction Chemicals- Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction

D•BASF The Chemical Company

Bridge Products By BASF Construction Chemicals - Building Systems Building Bridges for Durability

1. Corrosion Protection for PT Strands. Complete fill and protect PT ducts with Masterflow® 1205 distances.

cable grout.

High-flowability, easily pumped long

2. Bearing Pad Grouting - Highly flowable leveling grouts.

Masterflow® 928.

Easy install, especially in hot weather conditions

3. Protect PT Anchorage Blocks Coat with Sonoguard® Top Coat, flexible urethane waterproofing. 4. Patching P-T block outs and inspection points use Weather" rapid set.

)

"Set 45 Hot

5. End anchorage caps corrosion protection- Encapsulate caps with Masterf/ow® 648 CP Plus epoxy grout. 6. Anti-carbonization Coating Thorocoat smooth, a pure acrylic coating. Exceptional long-life, rich custom colors for beautiful bridges.

7. Segmental Epoxy Adhesives - Concresive® SBA 1440 series

Protection for 8. Chloride Concrete "Enviroseal 40" Silane waterbased penetrating sealer. 9. Bonding Bridge Overlays & cold joints, Concresive Liquid LPL epoxy. lO.Key Way grouting "Set® 45" magnesium phosphate based concrete. Non-shrink, chloride resistant and rapid setting even in freezing temperatures BASF Construction Chemicals - Building Systems 889 Valley Park Drive Shakopee, MN 55379 Customer Service 800-433-9517 Technical Service 800-243-6739


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12.4.1 BASF Construction Chemicals - Building Systems Epoxy and Prepackaged Grout for Segmental Bridge Construction

D•BASF

Bridge Repair

1. Crack Repair of Structural Elements Concresive® Standard SLV epoxy used for injection grouting of fine cracks. Structurally bonds concrete.

The Chemical Company

2. Heal and Seal Map Cracked Decks. Concresive® 2070 Methacrylate penetrates cracks, seals bridge decks and gets traffic lanes reopened with hours of application. 3. Repair Concrete Pavements, Bridge Decks, and Resurface Traffic Lanes - "Emaco® T-430" and "Thoroc SD2" mortar. 4. Dowel Bar Pinning of Joints in Concrete Roadways - Dowels are installed to pin jointed pavement sections together for the purpose of preventing bounce (and resulting wear) between pavement sections. "Set® 45" Manesium Phosphate based concrete. 3000 PSI in 1 hour. Non-shrink. 5. Piles, Pier Sections, Girder Repairs Three types of repairs are most common: • Small spalls - Emaco S88 silica fume mortar & Thoroc® HBA non-sag mortar. • Larger isolated areas - damaged caused by impact (over height vehicles) on the underside of Beams, Spalling caused by corroding steel reinforcing, deck areas joints. including spalling expansion Typically a highly flowable, shrinkage compensated, low permeability repair mortar is desirable. These mortars can for PUMPED or Poured into formed spaces. Good choices for beam and girder repair include "Emaco 566", "Thoroc LA 40" flowable, fast setting repair mortars. • Large area I volume repairs - vertical and overhead (not pavements), i.e. bridge abutments, protective seawalls, bascule bridge structures, piles etc .... Shotcrete repairs are often the best solution. Use "Shotpatch® 21F". 6. Corrosion Inhibiting Passive Galvanic I Cathodic Protection: Corr-Stops® easily installed zinc based corrosion mitigating anodes. BASF Construction Chemicals - Building Systems 889 Valley Park Drive Shakopee, MN 55379 Customer Service 800-433-9517 Technical Service 800-243-6739 Chapter 12.0- Epoxy Jointing, Duct and Duct Coupler Devices, and Prepackaged Grout

,~) 14 of 16

12.4.2 Sika Corporation Epoxy Resins for Segmental Bridge Construction Sika Corporation 20 I Polito Avenue Lyndhurst, NJ 07071 Tel: (201) 933-8800 Fax: (201) 933-6225 Email: [email protected] Web: www.sikaconstruction.com Sika Corporation is a worldwide leader in the construction industry specializing in systems for concrete repair, protection and structural strengthening. Sika offers products such as concrete admixtures, corrosion inhibitors, repair mortars, prepackaged grouts, sealants, adhesiveS, c0atings, and segmental bridge epoxies. Sikadur 31, SBA (Segmental Bridge Adhesive) has been used on most of the segmental bridges constructed in the United States and around the world. The specially formulated epoxies are available in Normal Set and Slow Set formulations for use in temperatures from 20 degrees F to 115 degrees F. Sikadur 31, SBA is a unique high-modulus, 2-component, moisture-tolerant, solvent free, epoxy resin. It conforms to the current ASTM C-881 requirements and ASBI Guidelines for epoxy resins. The range of products is as follow:

)

Normal Set

Slow Set

Sikadur 31, SBA (20-45F) Sikadur 31, SBA (40-60F) Sikadur 31, SBA (55-95F) Sikadur 31, SBA (80-115F)

Sikadur 31, SBA Slow Set (40-61F) Sikadur 31, SBA Slow Set (55-75F) Sikadur 31, SBA Slow Set (70-90F)

Figure 12.8- Applying Sikadur 31, SBA on Central Artery Bridge in Boston, MA


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12.4.3 Sika Corporation Prepackaged Grouts for Segmental Bridge Construction SikaGrout 300 PT is a high performance, zero bleed, sand-free, non-shrink cementitious grout with a unique 2-stage shrinkage compensating mechanism. It is non-

metallic and contains no chlorides. With a special blend of shrinkage-reducing and plasticizing/water-reducing agents, SikaGrout 300 PT compensates for shrinkage in both the plastic and hardened states. SikaGrout 300 PT is designed for use in horizontal and vertical grouting of ducts within bonded, post-tensioned structures. It can also be used to repair voids within ducts of post-tensioning strands for corrosion protection. With its high fluidity, SikaGrout 300 PT can also be use for grouting in tight clearances.

Figure 12.9- SikaGrout 300 PT being used in Segmental Bridge Construction Sikadur 42, Grout-Pak PT Sikadur 42, Grout-Pak PT is a prepackaged, three component, !00% solids, moisture tolerant epoxy grout specifically designed to seal and protect the anchorages of post-tensioning tendons on segmental bridge projects. Anchorage locations are commonly referred to as "pour-back" boxes. Sikadur 42, Grout-Pak PT is an impermeable epoxy grout that is resistant to chemicals, corrosion, impact, vibration and stress. Even when poured in mass, Sikadur 42, Grout-Pak PT has a low peak exotherm, meaning it safely cures with low heat development. It is a non-shrinking grout providing high compressive strengths.

Figure 12.1 Oa -Post-tensioned strand terminus

Figure 12.1 ObSikadur 42, Grout-Pak PT mixed in pail


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TABLE OF CONTENTS

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 13.0 GEOMETRY CONTROL

13.0 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.9.1 13.9.2

•...

Geometry Control General Casting Cell Geometry Control System Tools Used for Geometry Control Geometry Control of the First Pier Segment Field Survey Checking During Erection Systematic Error Achieved Profiles Pier Shaft Segments Temperature Effects Temperature Expansion and Contraction Temperature Gradient

3 3 7 12 13 13 14 15 15 15 15 18

) Chapter 13- Geometry Control

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TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 13.0 GEOMETRY CONTROL

Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure

13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20

4 4 6 7 8 8 9

Alignment Control: Set-Up Alignment Control: Set-Up (Continued) Setting Pier Segment from Ground Definition of Global Geometry Match-Cast, New-Cast and Bulkt)ead Joint in Global Structure Segments in Local Casting Cell Coordinates Cell Hardware and Survey Observations After-Cast Survey Observations- General Case A check for twist of the Match-Cast Segment Geometry Control Measuring Equipment Geometry Control for Starting (Pier) Segment Effect of Accumulation of Systematic Errors Alignment of Cantilever Structure (Three Span) Alignment of a Span-by-Span Structure Shimming Joints to Correct Profile Shimming Joints to Correct Profile (Continued) Geometry Control for Precast Pier Shaft Segments Temperature Expansion and Contraction Temperature Gradient Deflection Caused by Temperature Gradient

Chapter 13 - Geometry Control

10 11 12 14 14 15 16 16 17 17 18 19 19

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13.0 Geometry Control 13.1

General The geometry control of precast segmental bridges is achieved io the casting yard. The "shortline" casting system is based on making very fine adjustments to each match cast segment in the casting cell, and therefore requires precision; more so than the 11 }ong-line" system where the geometry control is maioly achieved when building the soffit. The following discussion concentrates on the "short-line" system since it is more commonly used, although the principles apply to both systems.

Precision geometry control has nothing to do with the sizes, thickness variations or tolerances of the component pieces of the segments, important though as these are to the overall quality of the finished product. The precision is required for measuring the relative as-cast position of the new segment in relation to its match cast neighbor. These measurements are critical. The setup required for this io the casting yard is shown in Figure 13.1. The aligmnent is controlled by an instrument on a permanent base and a permanent target. Neither instrument nor target should be disturbed throughout the production, otherwise control must be reestablished. For this, adequate bench marks should be maiotained. The casting cell is always plumb, level and usually square so the geometry control is established, mainly by positioning the old segment as prescribed by the castiog curve and as shown in Figures 13.2(a) and (b).

)

As the first segment is cast and the top slab has been fmished, four elevation bolts, A, B, C, and D, as well as two centerline markers, E and F, are installed. The following morning, the elevations of the tops of the bolts are recorded and the centerline is scribed onto the centerline markers. Now the segment can be rolled forward for match casting. After the first segment is moved to the match casting position, it is reset to the instructions provided by the casting curve. The centerline will be as it was before, unless the bridge is curved. In case of a curved bridge, an offset "0" is used as shown in Figure 13.2(a). The vertical curvature is handled similarly. But even if the bridge is flat, it is necessary to adjust for the deflections which occur during construction. As mentioned, the amount of adjustment to be made is determined by the casting curve which can be part of the shop drawings. Note that if the segment would be positioned in such a way that both centerline markers are in line with instrument and target and the bolt elevations are the same as those measured before the segment was moved, the segment would lioe up exactly with the next segment-to be poured. Geometry control for precast segmental bridges requires an excellent surveyor. He should be on the job daily and keep accurate records. In spite of his competence, his work should be meticulously checked by the inspector since errors are expensive and time consuming to correct. After the old segment is properly reset and the setup for the new segment is complete, the new segment can be cast. The following morning, the surveyor marks the center line and records the bolt elevations of the new segment. In addition, before the old segment is moved, the elevations of its bolts and its centerline position are checked to determine if the old segment has moved during casting the new segment. It is often noted that position changes of the "old segment" occur due to settlement of the soffit rails by the segment weight, due to vibrating of fresh concrete against it, or due to forces applied to it while closing the forms.


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"'f>'·

level boll

Old ,...gment

N.e w SErgment

---

-

lllS'lrument

llorbtoni.,J refe#Wl!Cf!

Levt!!l boll Ne-w .segment.

~;:S:~~;:~p=lo~ne

__________~-, OM segment

ELEVATION

Figure 13.1 -Alignment Control: Set-Up

/n•

Cenler line

•A IE

.

Form always

plumb, level

~c

ll.J

square

Segment rotalion

Amount of offset determines horizontal

·o·

curvature

Level bolls ~

n

-

1 ~Target

anrl usually

(a)

Old segment

-

lJ.

•Ne. w ..

'(b)

'

B D

1

"old"

Amount of till

rcurva l ure

l-r·

El.EVAT[(JN

Figure 13.2 -Alignment Control: Set-up (Continued)

Chapter 13 -Geometry Control

-r-

det-ermines vertical

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When constructing a bridge using girders or whole spans cast in place, it is normal practice to set forms to within 1/100 feet (1/8 inch) of the desired position duly corrected for anticipated deflections. Each new segment should be cast to stay within this tolerance based on as-cast surveys of the previous segments. As accuracy depends upon consistency, it is important that the same individuals make the critical"as cast" observations at the same time each day prior to stripping the forms ofboth the new and the old match cast segments. Usually, this is the first thing each morning before the daily crews arrive and when weather conditions are most stable from day to day. Note that all the critical readings are those after casting. While it is important to have an accurate set up before casting, this is unlikely to remain so during the casting operation. Some movement,

however slight, will occur, so the true achieved geometry is recorded after casting. It is possible to compensate for casting errors by adjusting the position of the next set up and so on. In fact, the major challenge in geometry control lies in keeping track of casting errors and correcting for them. Erection of the first segment, usually a pier segment, is critical and should be done as accurately as possible. This segment should be placed to an accuracy of Ill 000 feet. It is very important that all the information from the casting operations and the calculated "as cast"

actual relative positions of the segments be carried through the field erection process as well. This poses some practical difficulties because it is by no means as easy to obtain the same accuracy in the field as in the casting yard. However, the field setting is only required at each pier segment or start of a successive run, and it is worthwhile doing this correctly. Placing a large chunk of concrete with a crane to an accuracy of a few thousandths of a foot is difficult. In practice, it is possible to use shims, packs and wedges to maneuver the segments to an acceptable

)

accuracy. Also, by installing supplementary transverse alignment markers while in the casting cell, the horizontal adjustment ofthe pier segment can be set in the field using the base line of the full segment width, thereby not relying solely upon the shorter, front to back; longitudinal centerline marks (Figure 13.3). During erection, elevations and horizontal alignment should be checked to see if they are in agreement with the calculated as cast positions. If not, then adjustments may be necessary. Such compensations include: re-orienting or rotating the cantilever after erection, calculating a

compensatory setting for the next cantilever, or shimming the joints. The latter should only be used as a last resort as it can unpredictably lead to "correction of corrections," and so on. Moreover, it is not effective for short cantilevers or deep girders.


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liPrizont'BI' n.figumeul: -cont-rol by observation onlo P-I'e-sel lrt~nsverse

een-lertine

\

Figure 13.3 - Setting Pier Segment from Ground

Precision within the geometry control system is essential in order to avoid errors in the geometry of the structure. A source of error in aligmnent may arise from the deformation characteristics of the concrete being different from those assumed. Deformations of concrete are difficult to predict with any degree of accuracy, and most attempts are, at best, sophisticated judgments. In segmental construction the actual deflection can differ from the theoretical just as in precast girder production, where identical girders can differ in camber by a few inches. However, with precast segmental construction most of the shrinkage has usually occurred during storage, and the concrete has matured substantially by the time of erection. This helps to eliminate the significant variations likely with young concrete.


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13.2

Casting-Cell Geometry Control System

Geometry control is achieved in the casting cell by means of a system illustrated in Figures 13.1 and 13.2. The elevation control bolts A, B, C, Din Figure 13.2 are set over the webs as these are stable locations where no vertical deflection occurs from transverse flexure or post-tensioning. For example, wing tips can sometimes deflect upward by Y. inch from post-tensioning. Horizontal control is established by setting the match cast segment at the necessary skew at offsets measured at centerline hairpins E and F. Vertical alignment is set by adjusting jacks on the soffit carriage of the match-cast segment until the elevation bolts are above or below the plane of the top of the bulkhead by a desired amount. Normally, the geometry of a segmental bridge surface is defined by establishing three dimensional global coordinates (easting, northing, and elevation) at the centerline and equidistant to the left and right over each web at each joint (Figure 13 .4). These coordinates are directly calculated from the stationing, Instantaneous radius of curvature, longitudinal profile grade and snperelevation at each joint. Global elevations are adjusted for camber (the opposite of deflection). Normally, camber adjustment for global structural torsional twist is rarely needed but could be incorporated if necessary.

Geometry Control: 30, Define Structure Geometry

Global

v"""""

/

'

j'

Global Coordinates: E, N, Z at left, center, right at each joint

Figure 13.4 - Definition of Global Geometry


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Three consecutive joints defme the intrinsic geometric surface shape of two consecutive segmentsnamely: the previously made match-cast segment and the yet to be made new-cast segment.

Geometry Control: Relation Global Space to Cell Up

Station

Match Cast (M) and New-Cast (C) in Global Space

Figure 13.5- Match-Cast, New-Cast and Bulkhead Joint in Global Structure Geometry Control: Relation Global Space to Cell

Match Cast (MC) and New-Cast (NC) in Local Cell

Figure 13.6- Segments in Local Casting Cell Coordinates

Chapter 13- Geometry Control

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)

If it is assumed that the after-cast coordinates of the match-cast segment are already known from previous observations and calculations, it is a tedious but relatively straightforward mathematical process to imagine setting the cell-bulkhead at the desired position of next (new-cast) joint in global space (Figure 13.5) and transforming the global coordinates of the two known joints and the new desired (bulkhead) joint from 3-D global space to the local coordinates of the casting-cell. The latter are defined by the bulkhead and cell centerline (Figure 13.6). This transformation provides the set-up of the match-cast segment relative to the desired bulkhead location for the new-cast segment. To reference the new segment to the cell and facilitate after-cast observations, four new elevation bolts and two new centerline hairpins are placed in the top of the new-cast segment, close to match-cast joint and bulkhead. Those close to the bulkhead (bolts Ao and C, and centerline pinE,) define the position of the bulkhead joint. Those close to the match-cast face (bolts B, and D, and centerline pin F ,) relate directly to those next to them on the match-cast segment (Am, Cm and E.,) and thus to the previous bulkhead joint. Likewise, those at the far end of the match-cast segment (Bm. Dm and F.,) relate to the previous (A", C" and E" -not shown) and the previous bulkhead joint.

Geometry Control: Survey Hardware

r"rEie,effon Bolts

(Vertical Control)

Cefl

L..

Bulkhead

Face

'-''""'""on Top of Bulkhead (Typ.)

(shown for bulkhead perpendicular to chord)

Geometry Control Survey Hardware in Local Cell

Figure 13. 7- Cell Hardware and Survey Observations No set-up is ever perfect and match-cast segments always tend to move a little during casting. So, after casting, all bolt elevations are carefully surveyed relative to the elevations at the top of the bulkhead. The centerline of the casting cell is punch-marked into the centerline hairpins on the new-cast segment. Theoretically, these have an offset of zero (Figure 13.7) providing there is no mistake when punching. Regardless, all four centerline hairpin offsets are measured from the casting cell centerline. The length of the new-cast segment is measured along the webs between like-bolt (i.e. Ao to Am and from C, to C.,) - the average is used for the centerline length. This requires that all bolts always be set at a constant, short distance from the joints - and likewise the hairpins. And that elevation bolts always be a a constant distance ("W/2'') from the centerline. For length measurement, the same center-punch marks are used in the elevation bolts as used for setting the point of the survey leveling rod. Figure 13.8 summarizes the necessary after cast observations and includes the general case of a deliberate, or accidental, non-zero center offset at the match cast joint.

) Chapter 13 - Geometry Control

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Geometry Control: After-Cast Observations

Joint jj Previous

Ch Match-Cam Segment

Sight-line

Center Hairpin

A

Jomti

LeftLe

Ceil Left

Em

em

'=======~~-~m==~~~~--==~~~~-====--1 ~ B.c De New-cas!

Segment

Cell Righi

Right Length =Cctocm

cb

Standard 'd'

Fixed

Bulkhead

Non-Zero Offsets - regardless of radial or perpendicular

Figure 13.8- After-Cast Survey Observations- General Case Survey results are converted into coordinates local to the cell itself and then local to the cell-axes of the match-cast segment when it was newly cast. Using these match-cast cell-axes as a reference enables transformation from the cell to global space and provides the actual achieved "as-cast" location of the new bulkhead joint. The entire process is repeated for the next segment, and so on. This process- "3-D Coordinate Geometry Transformation Technique" -was originally developed at the Linn Cove Viaduct in 1979. For simplicity of construction and ease of operation, casting cells are almost always fabricated so that the bulkhead is perpendicular to the cell centerline. Also, the soffit form is rectangular and the web and wing forms operate parallel to the cell centerline- as in Figure 13.7. Horizontal aligmnent is attained by slewing the match-cast segment in plan- holding the centerline offset at the match-cast face at zero - while offsetting the far end face (remote from the bulkhead) by the desired geometric amount. This configuration places the bulkhead joint face perpendicular to the chord conoecting the centerline points of the new-cast segment. The resulting joints in the bridge are not on a radial line but are perpendicular to the chord- i.e. slewed off-radial one way or the other depending upon the direction of casting. Such joints are often referred to as "chord-perpendicular joints" as opposed to the alternative of "radial joints". For the general condition of any type of curvature, the calculation of global 3-D coordinate geometry is relatively sirople when joints are truly "radial" (Figure 13.4). However, in order that casting cells remain simple machines it is necessary to modify coordinates generated on a radial to chord-perpendicular coordinates prior to perfomting transformations from global space to the cell and vice-versa. The mathematical exercise involves interpolating (in 3-D) along the longitudinal lines of the left and right elevation control points, with some iteration, until the global coordinates of the joint lines are mutually perpendicular to the centerline chords. Since the direction to slew the joint depends upon the necessary or Contractor's elected direction of casting, this part of the process may await the actual casting. In the meantime, for information and geometry planning it is useful to have three-dimensional coordinates generated for radial joints provided on design plans - since this is the first step in a general process.

.J Chapter 13 - Geometry Control

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Observations are made to an accuracy of ±(J.OOl feet. It is recommended that readings are by two separate teams or lead surveyors. The alignment of the cell and elevation and attitude of the bulkhead should be checked regularly by reference to remote bench marks or survey points to guard against (unlikely but possible) error due to drift of equipment. Processing of numbers may be graphical or numerically by computer. It is recommended that a graphical plot to an exaggerated scale be run as a separate check against computations and to provide a visually recognizable warning in advance of error.

The above is a basic introduction to geometry control needs and techniques. It is not the intent here to present a full thesis. Geometry control calculations are tedious; they are best made by a computer program and further explanation would add little to this guide. Variations on the basic process are possible to accommodate situations where occasional elevation bolts and centerline hairpins cannot be placed in their desired locations to avoid construction details such as block-outs - or to accommodate breaks in superelevation across the width of the segment or an offset profile grade line - and so on. The key is always to respect that elevation bolts over the webs defme vertical control and centerline hairpins define horizontal control.

It is important that little or no twist is inadvertently introduced when moving a new-cast segment into the match-cast position- a simple check is illustrated in Figure 13.9

Geometry Control: Twist Error Twist: Set-Up of Match-Cast Segment Desired setting

~"'I :?>"'" - - -- -'

Inadvertent twisted setting

------.'it

G>·-----------------------.. .· ............... Bulkhead

For no twist set-up, check elevations: (Dm- Cm) +(Am- Bm).LAB = [De- Cc] + [Ac- Bc].LAB LCD LCD

Figure 13.9- A check for twist of the Match-Cast Segment


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13.3

Tools Used for Geometry Control (I)

Offsets: Centerline offsets are measured from the casting cell centerline using a metal scale fitted with a center point which sits in a pnnch mark on the hairpins. A spirit level shonld be attached to this scale so that it is set horizontal. Also, it should be held at right angles to the centerline of sight in the cell (Figure 13.10).

(2)

Elevations: Elevation readings on the bolts are made with a precision level placed on top of the fixed mounting, reading onto a leveling rod fitted with a scale divided down to at least .005 feet. In order to make sure the readings are taken at exactly the same point each time, the leveling rod should be fitted with a center point which sets into a punch mark in the top of the bolt.

(3)

Lengths: A steel tape is used for length measurement. It is advantageous to measure lengths between the center point marks on the hairpins, the distance between, adjacent hairpins and similarly along the bolt lines between the leveling pnnch marks. Readings should be estimated to at least .002 feet for length (Figure 13.8).

(4)

Lateral offsets to the level bolts should be measured from the centerline hairpins. It is preferable to have the bolt positions accurately marked on the bulkhead so that they are always at the exact required offset from the centerline (Figure 13.8). With care and precision, the readings obtained will allow precise processing using threedimensional coordinate geometry computations which are the most accurate when it comes to defining curved surfaces in space. Good recordkeeping is essential as well. There have been occasions when accidentally one or more of the geometry control hairpins or bolts were lost. This is not irretrievable. It is usually possible to continue construction by using known relative positions of adjacent undamaged markers. What it means is merely a little less predictable control over the erection aligmnent.

Spirit levelling bubble

~

Pfnely divided metal scale

I

pirit level.

~

~

~

. Cenler point c( ha,.,dend sl'eeJ

Center punc!J stirrup

HoNZ!J!!Iaf Qflsel$

Cenl-er point of h~t:delJ

ed steel ___

·an ball -

Figure 13.10- Geometry Control Measuring Equipment Chapter 13 - Geometry Control

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13.4

Geometry Control of the First Pier Segment The first segment of a run or a cantilever is cast between the bulkhead and a temporary bulkhead. Consequently, it has no match cast segment to which its geometric position can be referenced.

When moving this segment from temporary storage into the match-casting position, it is simply set to the same position it had after casting by reading the same elevation on the bolts and the same offsets on the markers; This gives a starting point from which all other segments can be subsequently referenced, assuming that there is no casting curve adjustment to be made. If there is a casting curve adjustment needed, it can be made at this time. The bolt and centerline marker readings are also used for setting the first segment in its required attitude in the erected structure. The technique is again part of regular geometry control procedures and will not be elaborated further here. The main feature of the first segment which, if it is a pier or abutment segment, is usually shorter than the typical segments, is to establish a transverse horizontal control line on the surface of the segment in the casting cell (Figure 13.11 ). This provides a greater base line length to align the segments in the field. The normal procedure is to determine either a radial line or a line parallel to the bulkhead and establish this on the center of the segment with horizontal alignment hairpins set as far out on the segment wings as possible. This requires that this line be observable on the bridge, either from above or from the ground below. In the latter case, the line has to be scribed onto the end faces of the wings, and two observation stations must be established on the ground on either side of the pier (Figure 13.13). Precise setting and checking of the first erected segment is essential since any error in its position

is magnified proportional to the ratio of the length of the cantilever or continuous run of segments and the transverse base line width.

) 13. 5

Field Survey Checking During Erection After the pier segment has been set and checked the horizontal and vertical alignment of successive segments must be checked as well. It is normal practice to calculate and measure elevations each time each segment has been erected. The horizontal alignment is also checked and

should match the theoretical horizontal geometry. The only errors occurring should be slight deviations due to casting errors and corrections. The overall line should closely track the desired

line. A generous tolerance should be allowed for the vertical alignment since this is subject to all kinds of variations due to construction loads, creep, shrinkage, temperature, post-tensioning variations,

and so on. However, the alignment should closely agree with the required alignment at the time of erection when duly corrected for these effects. It is difficult to put a precise figure on this tolerance as it depends upon the type of construction. For cantilever construction, the vertical

alignment should generally be within one- to two-inch per cantilever length of I 00 feet, and similar cantilevers should behave comparably. (This latter point is a guide to the accuracy of the initial material assumptions and calculations). Any substantial variations from line and level or any trends noticed early in the construction

should be subject to close study, and corrective action should be taken. The latter would include checking procedures for errors, especially systematic errors, amending casting curves for future

segments and perhaps shimming the joints with glass fiber matting to adjust the alignments. The use of shims is a "last resort" since it causes stress concentration on the segments and prevents the

joints from closing properly, which may cause problems during grouting.


13 of 19

Pre-determine and set lhis angle in the casling--cell

f f. C;rsling-cell - ----~

£1e•,.L1on bolts

I

I

...- Tempornry

lmlkl!ead

•

- [-.

.. Auxiliary llD irpins to_/ ll"iiiJSflei"'Se £

Casting-eel/ bulk/lead

scl

Alain longitudinal center line hairpiiJs

Figure 13.11- Geometry Control for Starting (Pier) Segment

13.6

Systematic Error It is worthwhile giving some consideration to the implications of making a systematic error in each casting operation either as a result of a computational method error or as a physical defect of the equipment which is systematically repeated in each segment of a nm. Figure 13.12 shows the effect which creates a total small systematic error (e). The final error after "n'' segments amounts to n(n-1 )e/2. In other words, a systematic error of .002 feet in each segment would amount to an off line error of .09 feet after 10 segments and .38 feet after 20 segments. Clearly, systematic errors must be avoided, and the use of proven techniques should be encouraged. e::;t•rror

---r

n-1

E

___L It can be_ slioivn lllal tile effect of

error

E.

1'1

sm<1/l consistent

conlmrwus/y r<'pealed, will accumulate to loll!/ error of E"' llJ!!:-:.IJe ., !!P e ,, ft er "11" segme11 Is 1f

2

2

·J

Figure 13.12- Effect ofAccumulation of Systematic Errors


11

14 ofl9

13.7

Achieved Profiles Figures l3 .13 and 13.14 illustrate the kinds of variations in cantilever and span-by-span profiles. Figures 13.15 and 13.16 show the means of correcting a profile by shimming a joint. It is emphasized that this should only be done if absolutely necessary as a last resort. It can lead to complications and is not entirely predictable.

13.8

Pier Shaft Segments Figure 13.17 shows one technique of observations for the aligmnent control while casting precast pier shaft segments. Other methods are possible by using inserts, plumb lines, leveling bolts, etc.

13.9

Temperature Effects

13.9.1 Temperature Expansion and Contraction A rise or fall in temperature will cause a structure to become longer or shorter. Bearings and road joints are designed to accommodate this movement.

In some cases this temperature effect may cause problems during construction. Figure 13.18(a) for example shows a structure with a fixed pier in the center: After the cantilever on this fixed pier is erected a connection is made to the remainder of the structure. The connection should be able to pull the erected part of the structure over its bearings in order to take care of the temperature movement. If the connection is not strong enough, the cast-in-place splice will crack (Figure 13.18(b)).

)

T/Jeorelical casting. curve to compensate

-------~

for anticipated

(a)

..

Canl.,fl ~------

---

+-

07 ___

deformations - - ,

+ .

=:.-----··--!__ __________ ·=

Required t/Jeoretic:al final grade

Actual ac/Jieved prome lime of construction

·~

Canl/2 ·-~---- ~ ----=-

3. Align 2nd.. cantilever to match first

(b)

Set side span segments lo match cantilever

4. Set 2nd side span segments to match 2nd. cantilever

{c) Figure 13.13 -Alignment of Cantilever Structure (Three Span)


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Actual

T/woretical

Span-by-span conslruc_tion is less sw:ceptibfe .to casting curve and castmg geometry discrepancies !han cantiJe.ver construction because there are lvpically fe.wer segmenls per ·span {tile spans

a"re usually shorter and segments longer} and tllere is usually a closure joint in earll Spall whicll pal·mils .some adjustment Also. !IJe structure is geJ~Prall.v stiller. Figure 13.14 -Alignment of a Span-by-Span Structure

Acl·ua-1 acl1ieved profile

t.hus fnr

-·-·-·-

r

ITT1

1'heroUt::al

re.quired .prolile

l---

"'

If observed profile do_es JJot mat·ch deslred and if it is -c/enr· tiJa-_l they will conlinue t-o diverge, l·hen some correc:tive ac:Uon is possible by

shimming the joints willl woven glass fiber matting embedded iii tile epo.•y. Usun-ltJ• -llw rcrnaining cantilever ·seg-me.-nts IJa ve a:IJ·ea(fy -been ca$l by ibis time ma-k-ing correcUons by cast-ing cOJnpe-ns:a-Ho-ns impossib-le. StJiJnming should be -doue only if a.bsolutelyr necx:Jssa_ry, and t-hen it shnuld be lwpl ·t-o a nJinim.um be.cnuse tis c./fee-l is not pred-ictnbie ruJCl t-lu~ l/Jicl
I

Sbou

Figure 13.15- Shimming Joints to Correct Profile

\J Chapter 13 -Geometry Control

16ofl9

1 Layer None Shimming jlJint trith wuven glass fibre mat.t:Jng lo pmlillde wedge shaped jlJinl to corr;ect sliltnment. It is r:ecoml'(leiJ.deq fh«1. no mare {han 2 laJil!rs tpsximum be u.s~d in any joint. Layering as shown would Up next segments

d.o•imwards. To tip next segments upwards. shim from bottom

Shiinming jninl,<; riuJ_J!

ott~asiona.llr

be ner:es$ary ·

in canUietrer constrUtill.ion. • ll is never liftel)' Lo be used in ol•her segmental construction i.e. span- by-span. Figure 13.16- Shimming Joints to Correct Profile (Continued)

) Mea-sure C10rner;- or

otbcr ,-eteren:ce Jhr.e, a[fsets fl'C!/11 '"u·.tfea/ planes Q

(9

.

Mil tell- c-asl

~

l (iJ )ObS"efVatioJis

5

r-- -It I!

1

.)

@ Scg.

Seg

®

.

,.

~-~-

0

-1r:_ r--

4 \

Seg 3

Seg, 2

Sec

I

Figure 13.17- Geometry Control for Precast Pier Shaft Segments Chapter 13 - Geometry Control

17 of19

13.9.2 Temperature Gradient A temperature gradient or temperatnre differential exists when a part of the structure has a different temperature than another part. This commonly occurs when the top slab of the box girder, which is exposed to the sun, heats up faster then the webs and the bottom, which are not directly exposed. Temperature differences of 30-40 degrees Fahrenheit can easily occur. As a consequence of this temperature differential, (shown in Figure I3.19(a)), the top slab wants to expand, but the bottom slab does not. As shown in Figure 13 .19(b), a girder will camber due to this temperature effect if supported at the ends. In case of a free cantilever, as shown in Figure 13 .19(c), it can be seen that the tips of the cantilever deflect. The amount of movement noted in the field increases with the length of the cantilever. A l-inch deflection, however, is common. Because of this effect it does not make sense to measure elevations any time after the structure has been exposed for some length of time to sun radiation. The only suitable time for measuring elevations during erection is at sunrise. The fact that the cantilever tips move as they are exposed to the daily temperature cycle also affects the timing of casting midspan splices (see Figure 13.15). The best way to do this is:

(I)

connect the cantilevers at the tip by means of a strong back, as shown in Figure 13.20

(2)

cast the splice when the deflection at the cantilever ends is the greatest (say 3 p.m.)

(3)

At sunrise, the next day stress as mauy tendons as allowed by the strength of the "still green" concrete. Usually this is two or four tendons, which is enough to compress the splice so that the subsequent temperature deflection will not crack the concrete at the splice at the bottom.

If the splice were cast in the morning, it is possible that the temperature effect will crack the bottom of the closure joint before the day is over.

Figure 13.18- Temperature Expansion and Contraction


18ofl9

Exposed l
'%*'

(b)

Not exposed, temperature=

r·

(a)

{c)

Figure 13.19- Temperature Gradient

)

n

n

n II

:J p. m

n

(appro.< I

10 p.m. (appro.><)

Figure 13.20- Deflection Caused by Tl!ltlperature Gradient

..

) Chapter 13 -Geometry Control

19 ofl9

)

TABLE OF CONTENTS

\

j

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 14.0 BEARINGS AND EXPANSION JOINTS

14.0

Bearings and Expansion Joints

3

14.1

Bearings

3

14.1.1 Bearing Installation

3

14.1.2 Mortar Pads

6

14.1.3 Horizontal-Position of Bearings

6

14.1.4 Temperature Adjustment

6

14.1.5 Direction of Movement

6

14.2

7

Expansion Joints

14.2.1 Strip Seal Systems

7

14.2.2 Molded, Steel Reinforced Rubber Cushion Bolt-Down Systems

\

I

(Transflex or Waboflex)

8

14.2.3 Modular Joint Systems

9

14.2.4 Finger Joints

10

14.2.5 Bearings and Expansion Joints Supplied by The D.S. Brown Company

12


13

14.2.6 Expansion Joints Supplied by Freyssinet LLC

14

14.2.6 Expansion Joints Supplied by Freyssinet LLC

15

14.2.7 Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation 16 14.2.7 Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation 17

Chapter 14.0- Bearings and Expansion Joints

I of 17

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-5UPPORTED BRIDGES CHAPTER 14.0 BEARINGS AND EXPANSION JOINTS

Figure 14.1

Neoprene Bearings

4

Figure 14.2

Pot Bearings

5

Figure 14.3

Standard Design Strip Seal System

7

Figure 14.4

Strip Seal Joint System

7

Figure 14.5

Transflex Joint

8

Figure 14.6

Modular Joint

9

Figure 14.7

Standard Movement Modular Joint

9

Figure 14.8

A Multiple Direction Movement and Seismic Modular Joint

10

Figure 14.9

A Typical Finger Joint

11

)


2 ofl7

14.0 Bearings and Expansion Joints Bearings and expansion joints are provided to allow the structure to expand and contract. In addition, bearings transfer the loads from the superstructure to the substructure. In general, bearings and expansion joints are the most vulnerable parts of a structure. Expansion joints are subject to much wear and tear by traffic and cause many maintenance problems. Bearing and expansion joint devices supplied by the D.S. Brown Company and Watson Bowman Acme Corporation are presented in Sections 14.2.5 and 14.2.6, respectively. Bearings and expansion joints are specified on the plans. Usually a drawing of the type ofbearing or expansion joint required is included with the note that an "approved equal" may be substituted. In addition, special provisions should provide a detailed description regarding material quality and tolerances.

Since the product supplied is seldom equal to that shown on the plans, the contractor will submit shop drawings which will be provided to the inspector for his use in the field after they have been approved. Upon delivery to the site, the inspector needs to verify that the product is in agreement with the shop drawing and is properly installed.

14.1

Bearings There are two types of bearings commonly used on segmental bridge projects: neoprene bearings with or without sliding pad, and pot bearings. Neoprene bearings are more desirable bearings for their simplicity of installation and maintenance-free performance, However, both load bearing and movement capacity limit the application of neoprene bearings to short spans and short distances between expansion joints.

Neoprene bearings with sliding pads have more movement capability and therefore allow longer distances between expansion joints (see Figure 14.1). Pot bearings are available for large loads and movements and is therefore the type of bearing most used. Pot bearings consist of a base plate containing a rubber cushion inside a low cylinder or ring which allows a small rotation in the base plate. This is the reason for the name "pot" bearing. The

top plate rests on a piston which rests on the rubber cushion inside the cylinder. Since this rubber disc is under high pressure, a seal is required to prevent the rubber from squeezing out of the "pot." The top plate can have one of three arrangements either allowing or preventing movement:

fixed, free or guided. A typical fixed bearing which does not allow movement, a free bearing, and a guided bearing are shown schematically in Figure 14.2. Bearings are usually bolted down to the pier and have dowels at the top to provide horizontal fixity to the structure. 14.1.1

Bearing Installation Important items for bearing installation are:

)

•

Mortar pads below and above the bearings

•

Horizontal position of bearings

•

Temperature adjustment

•

Direction of the movement of the bearing

•

Blackout details in segment and pier

\


3 of 17

Figure 14.1 -Neoprene Bearings

·..


4 ofl7

)

Pot Plate

F'IXEO*

(No movement)

Sole Plate Guide Bars

Piston Masonry Plate UNJ~OtRECTiONAL.

EDGE:·GUIOED

(One direction movement)

) Teflon/Stainless Steel Sliding Surface

Sealing Rings

Elastomeric Disc

MULII·OIRECTICNAL*

(Movement in all directions)

* NOTE Masonry plate excluded for clarity Figure 14.2 -Pot Bearings

·~) Chapter 14.0- Bearings and Expansion Joints

5 of17

14.1.2 Mortar Pads Bearings transmit heavy loads from the superstructure to the substructure. This means that the substructure and superstructure concrete on both sides of the bearings is highly stressed. Uniform distribution of flowable material or dry pack to assure uniform distribution of loads on bearings is critical. Both neoprene and pot bearings are usually installed with mortar pads both below and above the bearing. The reason for this is that neither the top of the pier nor the bottom of the structure can be built with a small enough tolerance to allow installation without these. The materials used for these mortar pads are usually specialty mixes which have high early strength and low shrinkage properties. The material is subject to approval. The mortar strength required when used with Neoprene pads is 3000-4000 psi while 6000 psi is common when used with pot bearings. Most importantly, the mortar pad should provide uniform bearing under and above the bearing and should therefore be without voids. This requires both good workmanship and inspection. Specifically in case of poured or grouted joints a full scale test of the grout placing procedures is recommended.

14.1.3 Horizontal-Position of Bearings Bearings are usually installed horizontally. The reason is that a structure placed on bearings which are installed on a slope has the tendency to move. 14.1.4 Temperature Adjustment At the time of installation, pot bearings should also be adjusted for the temperature of installation. The designer of the bridge assumes installation at the average ambient temperature and calculates how much the bridge will expand or contract and, therefore, how much the bearing will need to be able to move either way. If, contrary to the assumption the bearing is installed in for example the coldest possible time of year, it can be expected that the bridge will just expand when the temperature rises. In this case, the bearing top plate will need to be shifted so that the full temperature movement becomes available for expansion. This explains why there usually is a need for a temperature adjustment. Temperature adjustments must be shown on the approved shop drawings.

14.1.5 Direction of Movement Guided pot bearings, which allow movement in one direction only, need to be installed in such a way that the direction' of the movement of the bearing is the same as the direction of the movement of the bridge. In case of straight bridges, this is the bridge axis. In case of curved bridges, however, this is not necessarily so and an instruction should be provided on the plans regarding the direction of movement. There usually is some tolerance on the movement direction because of the fact that the space between guide bars is usually about 118 inch larger than the top plate of the bearing sliding between it. This amount can also be specified.

This 118 inch space should be carefully divided into two equal amounts on each side. ofthe top plate and preferably kept constant with wooden inserts until the bearing is placed. The guides now have some movement capabilities both ways and some tolerance to tum.


6 ofl7

14.2 Expansion Joints Adjustments as discussed for bearings must also be made for the expansion joints. The types of expansion joints used on segmental bridges are: • Strip seals or movements up to 3 inches • Molded, steel reinforced rubber cushion bolt-down systems, (Transflex or Waboflex), for movements up to 13 inches • Modular joints for movements up to 52 inches • Finger joints for movements up to 12 inches

14.2.1 Strip Seal Systems A standard design Strip Seal System is shown in Figures 14.3 and 14.4. Zl
I

I

Figure 14.3 - Standard Design Strip Seal System

)

Neoprene Sealing Element

Steel Rail Profile

Figure 14.4 -Strip Seal Joint System This joint sealing mechanism is widely accepted in the construction indnstry as an effective and versatile expansion joint sealing methodology for movements up to three inches. The Neoprene sealing element is


7 of17

mechanically locked within a machined edge rail cavity with an anchoring arrangement suitable for current design code requirements.

The steel edge member(s) shall be A-588 or A-36 grade steel with a galvanized finish. The strip seal edge member cavity which accepts the Neoprene sealiog element locking lug shall be machined to fully engage the sealing element and prevent leakage. The Neoprene sealing element shall be additionally adhered with a single component moisture curing adhesive. Proper grade and temperature adjustments shall be made at time of joint setring in accordance with the manufacturer's recommendations as outlined in the shop drawing submittals. The advantages provided by a Strip Seal System are simplistic design, movement versatility, armored edge protection, and mechanically locked in place Neoprene sealing element. 14.2.2 Molded, Steel Reinforced Rubber Cushion Bolt-Down Systems, (Transflex or Waboflex) The Transflexjoint is shown in Figure 14.5.

Figure 14.5- Transjlex Joint The low profile design, large movement capacity of the Molded, Steel Reinforced Rubber Cushion BoltDown System provides versatility in application. Current cartridge anchor technology enhances the durability of the system in today's aggressive traffic enviromnent. Minimal blockout recessing, even for larger movement requirements, combined with basic design which is devoid of moving or mechanical accessories may satisfY designers looking for product simplicity. Disadvantages may encompass the proper temperature adjustment settings necessary during construction and the force requirements to open and close the molded system. Approximately 2,000 pounds per foot force is required to completely close the molded system on larger, (greater than 6 inches of movement) systems. A normal bridge width of 42 feet would, therefore, require 40 tons of horizontal force applied at the top of the abutment backwall. This would require special design of the end bent. Consequently, the Transflex or Waboflex Systems cannot be readily substituted for other joint designs without end bent redesign considerations.


8 of17

14.2.3 Modular Joint Systems

Figure 14.6- Modular Joint A standard movement modular joint is shovm in Figures 14.6 and 14.7.

Figure I 4. 7- Standard Movement Modular Joint A multiple direction movement and seismic modular is shown in Figure 14.8.


9 of17

0

0

0

Figure 14.8- A Multiple Direction Movement and Seismic Modular Joint Standard Modular Joint Systems The term Modular Joint System is used to describe a large movement mechanical joint which takes large movements and breaks them into equivalent small movements within each "module" or "cell" which . comprises the Modular Joint System. The overall design is a matrix of surface beams conoected to below grade support bars, which ride back and forth within support boxes during thermal movement variances. Located between each roadway surface beam is a mechanically locked sealing element which provides effective joint sealing during thermal movement differentials. Thronghout the past decade, manufacturers, researchers, and transportation officials have developed life cycle performance fatigne standards supported by test procedures, which should be performed and documented by any acceptable and reputable manufacturer of modular expansion devices. This program of performance documentation assures the client of reputable performance based upon an acceptable industry and design criterion. Additional quality control initiatives should prohibit the subcontract mannfacturing of modular expansion ·devices, coupled with quality manufacturing initiatives by manufacturers. Multiple Direction Movement or Seismic Modular Joint Systems Long span and curved structures may incorporate non-linear movements or seismic movement requirements, which can be satisfied by utilizing multiple direction or seismically designed modular expansion devices. Currently, manufacturers have developed, tested, and implemented these systems on

structures throughout North America and Latin America. Aoy product design considered for project utilization should be tested for individual and simultaneous multidirectional and accelerated movements. Additional life cycle fatigue testing should be required, which would verify performance capabilities in accordance with current design and industry standards. Installation of Modular Systems should be performed in accordance with the requirements of the manufacturer. Documented procedures should be provided to the contractor, preferably as part of the shop drawing submittal process. It is recommended that a qualified factory representative be on site during the initial joint placement, adjustment, and setting. 14.2.4 Finger Joints A typical fmger joint is shown in Figure 14.9. A finger joint consists of two steel plates either burned or machined to accommodate thermal movement requirements, which are attached to the bridge and the end bent. The fingers of the steel joint traverse the joint opening and are shaped to minimize the openings between the two plates. It is recommended that any finger joint design incorporate a mechanically locked in place, sealing device to prevent the intrusion of corrosive chemicals.

Finger joints tend to be generic in origin and manufactured by steel fabrication companies as per project specific design requirements.


10ofl7

Careful placement and installation is required to assure appropriate structural support beneath the finger plates. Additional care is necessary to align the fingers to assure linear movement and prevent misalignment and possible damage. The principal disadvantage of finger joints is trough location and the inability to effectively maintain and clean below grade troughs.

Figure 14.9 -A Typical Finger Joint

)

\


11 ofl7


The D.S. Brown Company - Manufacturer of Expansion Joints, Bearing Assemblies and Specialty Products Bridge Products: D.S. Brown's extensive product line includes: Steelflex® Modular Expansion Joint Systems, Versiflex~ Bearing Assemblies, Cableguard~ Elastomeric Wrap, Exoderrnic® Bridge Deck, Fiberbond~ FRP (Fiber Reinforced Polymer) System and other specialty products. D.S. Brown is fully integrated, performing and controlling all requirements of a project internally: •

RESEARCH AND DEVELOPMENT

•

ENGINEERING DESIGN/CAD DETAILING

•

RUBBER COMPOUNDING, MIXING, EXTRUDING AND MOLDING

•

CUSTOM STEEL FABRICATION AND MACHINING

•

LOAD TESTING

Expansion Joint Systems Steelflex® Modular Expansion Joint Systems D.S. Brown's Steelflex® Modular Expansion Joint Systems are highly engineered assemblies which consist of Steelflex® center beams and edge beams. The center beams and edge beams not only carry the dynamic wheel loads but also accept the series of strip seal style sealing elements that create a watertight joint. All Steelflex® Modular Expansion Joint Systems are desigued to accommodate up to 80mm of movement per neoprene sealing element.

Steelflex® Modular Expansion Joint

Steelflex® Strip Seal Expansion Joint Systems For decades, cast-in-place Steelflex® Strip Seal Expansion Joint Systems have provided superior watertight performance and longevity over boltdown, segmental and pourable expansion joint systems. Because of this proven performance, Steelflex® Strip Seal Expansion Joint Systems have become the overwhelming choice of owners and specifying engineers around the world for accommodating up to five inches (127mm) of total structural movement.

Steelflex® rail profiles are one-piece construction, manufactured using innovative hot rolled/non-machined and hot rolled/machined technology. All proprietary steel rails are available in ASTM A36 or ASTM A588 steel grades.

Anchorage Illustration

Delcrete TM Elastomeric Concrete/Steelflex® Strip Seal Expansion Joint System Components to this system include: low profile SSA2 or SSE2 Steelflex® rail profiles and Delcrete'" Elastomeric Concrete.


12 of 17

..

·

)

14.2.5 Bearings and Expansion Joints Supplied by The D.S. Brown Company (Continued)

Bearing Assemblies D.S. Brown is one of the leading suppliers of structural bearing assemblies. With extensive experience and utilizing the latest technologies, D.S. Brown can efficiently design, manufacture and test Versiflex= HLMR pot-style, spherical and elastomeric bearing assemblies for all types of construction.

Versiflex"' HLMR Bearing Assemblies Versiflex= HLMR pot-style bearing assemblies are suitable at locations where low profile, high-load bearing devices are required. Versiflex'" HLMR bearing assemblies are especially suited for curved or skewed bridges and other complex structures where the direction of rotation varies or cannot be precisely determined.

Versiflex 1M HLMR Bearing

Versiflex"' Elastomeric Bearing Assemblies For nearly 50 years, elastomeric bearing assemblies have been used in the construction of new bridges and the rehabilitation of existing structures. Other applications include: buildings and arenas, shear-key bumpers, seismic isolation protection and vibration devices for machinery.

) V ersiflexTM elastomeric bearing assemblies are custom

Versiflex™ Elastomeric Bearing

molded using neoprene or natural rubber and are categorized into three basic designs: non-reinforced, laminated and sliding bearing assemblies.

Versiflex"' HLMR Spherical Bearing Assemblies Versiflex= HLMR spherical-style bearing assemblies are most commonly utilized at locations where very high vertical loads and/or large structural rotations are present. Specific Design Features include: •

Use of woven PTFE (Max pressure of 5500 psi)

•

Rotation capabilities in excess of+/- 0.03 radians

•

Fixed, guided and mobile designs are available

For more information on these products as well as the entire D.S. Brown product line:

The D.S. Brown Company 300 East Cherry Street North Baltimore, Ohio 45872


Versiflex™ HLMR Spherical Bearing Assembly

P: 419.257.3561 F: 419.257.2200 Email: [email protected] URL: www.dsbrown.com

13 of 17

14.2.6 Expansion Joints Supplied by Freyssinet LLC Freyssinet LLC 1422'1A Wilim-dRoud- Suite:400 -CHANTILLY VA 20151 -USA Phone.: +l {703) 378-2500 }:ax; +I (703) 378-2700 ComttW'citJI CMtm:t :_frqssine1@frey$$1tutusa.cum

CIPEC Expansion Joints PIUNQPU: CIPEC expansion joints are designed to enable continuous tmffic between iwo structures, necommoduti:ng Slnlcttlrtll movements due to-creep. shrinkage effects,. temperature variations and defummtions under live load. ibey are Sllitable for -all rein:fOJ'Wd ooncrete, prestressed conen:te, -composite and !lteel :struelures, and particular1y f-or bridge decks. CU'EC expansion joints .ore also designed ro allow sufficient venical mov-ement to enable bearing replacement wllbunt di!laS.Sembty of the ~on joint.

EC•vid< dmlr.a.o for runoff water and are deslgned to minimize troffie noise.


14ofl7

14.2.6 Expansion Joints Supplied by Freyssinet LLC (Continued)

Q\4\l.U'Y ClPEC jcints are designed fur quality, with a proven history of durnbility and reliability :as demonstrated by the satisfactory performance in a wide variety of structural projects fur more than 30 years. CrPEC joinl" offur. • Excellent traffic comfort, • Protection ofsurfaces under the joint,. • Long life, • Good resistance to hea\.'}' duty aM •l..ow noise. frequent traffic loads, • High resistance to corrosion, • Adaptabnity to all surface materials. • No horizontal reaction, • Easy installation on new or old $1ructufes, • Vertical movements of the structures (fur jncking, etc.) • Minimal service and/or maintenance. \vjtbout lhe need to disasscrnbJ~: \be join~

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95 59'

15ofl7

14.2. 7 Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation Background Information Located in Amherst, New York, Watson Bowman Acme Corp. has been at the industry forefront of design and manufacturing expansion control devices for the bridge construction industry. From its modest beginnings in the 1950's, designing small movement pavement seals for concrete highway applications in New York, to producing today's state of the art large movement seismically designed modular expansion joint devices on the world's largest segmental concrete structures. Watson Bowman Acme has provided technical support and product solutions for the most complex and challenging applications. As an ISO 9001-2000 Quality Certified Company, Watson Bowman Acme quality initiatives provide a focus on continual improvement and relentless customer objectives. Over 90 employees are dedicated to design, manufacture, sales and service of bridge expansion control systems, and related fabricated steel products, such as. hand rail, scuppers, drains, and miscellaneous steel requirements.

Watson Bowman Acme provides product selection and related performance, sizing and costing recommendations for engineering firms and contractors. Watson Bowman Acme has been selected as a product supply partner on some of the most prestigious segmental concrete bridges and design/build projects in Norlb America. The Cooper River Bridge, New Susquehanna River Bridge, and Four Bears Bridge are a sampling of projects utilizing Watson Bowman Acme products and services.

Large Movement Modular Joint Installation Procedures Large movement modular joint systems are custom designed and fabricated to the geometry and movement requirements of each construction application. The long term performance capability of these devices in effectively waterproofmg, preventing substructure corrosion, maintaining structural integrity throughout designed movement cycling and traffic loads is based upon the integrity of contract specification, manufacturing and contractor installation. The most overlooked area of specifications is the recommended installation procedures for large movement modular devices. The following key installation items are generic and universally apply to all large movement modular expansion joint devices. Modular Expansion Joint Installation Punch List I.

Manufacturer shall provide shipping and lifting assemblies for jobsite handling of modular expansion joint devices.

2.

Temperature adjustment chart and placement instructions should be included in shop drawing submittal package.

3. Manufacturer should identifY lift points and lifting requirements for handling and maneuvering modular joint assembly at jobsite. (Figure I) 4.

Hardware for opening and closing joint assembly in accordance with temperature adjustment shall be supplied by manufacturer. (Figure 2)


16 of 17

11.2. 7 Bearings and Expansion Joints Supplied by Watson Bowman Acme Corporation Continued

Figure 1 5.

6.

)

Figure 2

Appropriate hardware for placement and grade setting of modular joint assembly must be identified, communicated and agreed by the supplier and contractor. Contractor shall inquire of manufacturer, any proprietary innovation or methodology to assist or facilitate installation efficiencies.

7. After temperature adjustment and grade setting of modular joint assembly, the contractor must effectively place formwork around joint assembly in blackout area in preparation of closure concrete pour. (Figure 3)

8. Formwork must be placed to assure protection and integrity of support box openings, preventing concrete intrusion within modular joint assembly support boxes. Rebar must be tied into support boxes, (Figure 4)

9. All shipping and placement hardware is removed after closure pour is complete and cured.

Figure 3


Figure 4

17 of 17

.)

TABLE OF CONTENTS

)

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 15.0 LESSONS LEARNED 15.0

Lessons Learned

3

15.1.0 General

3

15.2.0 Design Lesson Learned 15.2.1 Reinforcing Details 15.2.2 Tendon and Duct Detailing 15.2.3 Cracking 15.2.4 Designing for Construction Tolerance 15.2.5 Principal Stresses and Web Shear 15.2.6 Flange Shear Stresses 15.2. 7 Asymmetric Sections and Rotated Principal Axes 15.2.8 Shear Distribution of Multiple Webs 15.2.9 Shear Lag 15.2.10 Combination of Transverse Bending and Shear 15.2.11 Built-in Loads 15.2.12 Tendon Losses 15.2.13 Bottom Slab Drainage Details 15.2.14 Inspection Access

4 4· 4 6 7 7 7 9 9 9 10 10 10 10 11

15.3.0 Construction Lesson Learned 15.3.1 General 15.3.2 Equipment Requirements 15.3.3 Construction Loads 15.3.4 Truss Stability 15.3.5 Bearing of Truss Supports 15.3.6 Warping Under Concentrated Loads 15.3.7 Out-of-Balance Moments 15.3.8 Alignment and Geometry Problems 15.3.9 Geometry Control in Gore Regions 15.3.10 Fit of Match Cast Segments 15.3.11 Steam Curing and Warping 15.3.12 Short Tendon Elongations 15.3.13 Tendon Blockages 15.3.14 Tendon Pop-out 15.3.15 Epoxy Not Setting 15.3.16 Freezing of Water in Ducts and Recess Pockets

12 12 12 12 13 14 14 14 14 15 15 15 16 16 16 18 18

15.4.0 References

19

Chapter 15. 0 - Lessons Learned

I ofl9

TABLE OF FIGURES

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 15.0 LESSONS LEARNED

Figure 15.1

Reinforcement to Prevent Deck Delamination

4

Figure 15.2

Reinforcement at Angle Change in Bottom Slab

5

Figure 15.3

Tendon Deviation Reinforcement at Blisters

6

Figure 15.4

Cracking Due to Shrinkage

8

Figure 15.5

Cracking Near Blisters

8

Figure 15.6

Cracking at Transverse Post-Tensioning Anchorage

9

Figure 15.7

Pending of Water in Bottom Slab of a Segmental Bridge

10

Figure 15.8

Inadequate Inspection Access

11

Figure 15.9

Gantry Support Instability

13 6

Figure 15.10

Closure Error between tips of Deck Cantilevers- 1980<

Figure 15.11

Effect of Misalignment of Tendon Ducts

17

Figure 15.12

Curvature Pressure Exerted by Tendons

17

>

15

.J Chapter 15.0- Lessons Learned

2 of 19

--)

15.0 Lessons Learned 15.1.0 General The purpose of this chapter is to outline construction problems that have occurred in the past, with the objective of avoiding repeated instances of these problems in the future. Many construction problems have resulted from design and detailing oversights or errors. Some design and detailing oversights also impact the functional use of the structure in service. On the other hand, construction problems have often resulted due to procedures and practices under the control of the Contractor or the Construction Engineer. These categories of problems are discussed below under the headings of"Design Lesson Learned" and "Construction Lessons Learned".

Chapter 15.0- Lessons Learned

3 of 19

15.2.0 Design Lessons Learned 15.2.1 Reinforcing Details Interferences of embedded items, including rebar, post-tensiomng tendons, and miscellaneous construction hardware, are a common cause of construction problems, particularly dnring construction of heavily congested areas at or near piers. Under the AASHTO LRFD Bridge Desigu and Construction Specifications(ll('l", responsibility for interferences between embedded items shown on the contract drawings is the responsibility of the Engineer of Record. Extensive use of 2D and 3D integrated drawings, as well as extensive use of cut sections, is necessary during the design process to eliminate interferences between embedded items. The Contractor assumes responsibility for interferences in embedded items to the extent that the interferences result from changes made by the Contractor to the details shown in the contract drawings.

*Number in raised parenthesis refers to references listed in Section X of 0.

15.2.2 Tendon and Duct Detailing Many of the detailing issues for segmental design are directly related to successfully integrating the posttensioning tendons. Tendons can exert a significant force on the section wherever they deviate, be it by

desigu or unintentional. It is important to design and detail to mitigate typical problem areas, in addition to taking particular care dnring casting. The presence of numerous internal tendons in balanced cantilever structures raises the potential for certain types of delamination, where the tendon force causes a portion of the flange to separate from the segment. The frrst type is in the upper and lower flanges, where segments near the pier segment or mid-span house multiple tendon ducts. This translates to a significant portion of the flange that is effectively voided dnring erection, as grouting is generally not performed until the cantilever is complete. The multiple voids create a weak plane that can lead to splitting of the flange. This can be mitigated by adding "J" ties to secure the top and bottom mats ofrebar (see Figure 15.1). Generally, this is only a concern with longer spans, where the ducts would constitute a significant fraction of the flange area. Particular care is necessary in long span cast-in-place balanced cantilever bridges with a large number of ducts near piers.

HALF SECTION

Figure 15.1 -Reinforcement to Prevent Deck Delamination

.··)·· '·--


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Another area where delamination should be addressed is in the bottom flange of variable depth segments. The change in angle at the segment joint creates a natural deviation in the bottom flange tendons. This deviation bas a tendency to pull out, delaminating the bottom flange. Supplemental stirrups are required in the vicinity to restrain the deviating tendons. A common configuration is shown in Figure 15.2.

BOTTOM FLANGE

SECTION

LONGITUDINAL SECTION

Figure 15.2 - Reinforcement at Angle Change in Bottom Slab An area that requires particular attention is the toe of the anchorage blisters. This region typically includes a relatively shaip deviation of the continuity tendon anchored in the blister (see Figure 15.3). As the tendon deviates, it exerts a radial force on the concrete, effectively trying to straighten. This deviation must be tied back into the segment flange to avoid cracking. It is the responsibility of the designer to provide adequate steel for this force, and care should also be taken in the casting yard to ensure that the steel is well distributed along the full length of the deviation.

) Chapter 15. 0 - Lessons Learned

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A

Hairpins

[l

"ilai-rpins

~

.-:JIIO\IL '

Sec-lion A CurVl!d pa-,.1 of te-ndon mu~t be /CC'ated in b/Jster Hail'pin r~inforcmg concentrated in <'ut'VC' of tendon leug{h.

Figure 15.3 - Tendon Deviation Reinforcement at Blisters These examples of common critical details do not constitute an exhaustive list. It is important that good engineering judgment be used in developing segmeot details, and that critical details are clearly shown in the plans and carefully implemented in the casting yard. Specific requirements for many of these details are given in the AASHTO Guide Specifications for Design and Construction of Segmental Bridges, and in the AASHTO LRFD Bridge Design Specifications.

15.2.3 Cracking Cracking occurs often in concrete structures for a variety of reasons. When noticed, cracking should always be reported to the engineer so that the cause may be detemtined. Some common causes of cracking are;

• •

pouring new concrete against old concrete the introduction of high forces, for example, at post-tensioning blisters

• •

cracks near post-tensioning anchors cracks caused by structural defects

Figure 15.4 shows the situation where new concrete is cast against old concrete. This, of course, occurs at

every cast-in-place joint. Cracks as shown may appear. These are shrinkage cracks which are difficult to avoid. To control the cracking, additional reinforcing steel or transverse post-teosioning may be provided near the joint faces in the cast-in-place concrete

Figure 15.5 shows crack patterns, which may occur at blisters where high forces are introduced into the concrete. This type of cracking may be reduced or elintioated by locating blisters at slab-web intersections, by limiting the force (number and size of strand) anchored in a single blister, and by use of rebar to control crack width. Figure 15.6 shows cracking at a post-tensioning anchor. Concrete at anchors placed on the edges of thin slabs is susceptible to cracking. Teodon sizes should not be larger than 4x 0.6-inch-diameter strands on a nine-inch-thick edge. The anchorage area is normally reinforced to control or elintioate this cracking.


6 ofl9

15.2.4 Designing for Construction Tolerances From a design perspective, it is often desirable to minimize flange thicknesses to reduce overall demand. In doing so, it is important to consider all the tendons and reioforcement that might overlap in a given section. A common example is integrating the longitndinal and transverse tendons, along with perpendicnlar mats of steel on the top and bottom face. In doing so, it is important to use realistic assumptions of the duct outer diameters and construction tolerances.

15.2.5 Principal Stresses and Web Shear Shear design of webs is generally achieved through au analysis of ultimate demand and capacity. However, it is prudent to perform a check of the service-level stresses in the webs to ensure that there is adequate concrete area to avoid cracking. A useful tool for this check is to verifY the principal stresses in the webs under service load combinations. This procedure, which is required by Article 5.8.5 of the AASHTO LRFD Bridge Design Specifications, ensures that the webs are adequately proportioned. The effects of torsion should also be considered in this check, due to their contribution to the overall shear stresses in the webs.

15.2.6 Flange Shear Stresses For a constant web thickness, it is generally necessary only to verifY shear stresses at the centroid, where shear stresses are at a maximum. However, it is also prudent to verifY the shear stresses in the top and bottom flanges adjacent to the webs. While the shear stresses in these areas may not be as high as other areas in the web, a decreased thickness can lead to unacceptably high shear stresses. This is frequently the case in the bottom flauge, which can be very slender for sections in positive bending. A local thickening of the bottom flange can be effective at preventing cracking at this location.

)


7 of 19

Shrinkace cracks, control by trans:verse pas!-- tenso I ning

or rein-forcing

·~·

~ w I~

Precast

seg~ents

J.

Precast. segm~nls-

L

.J

cast-in-place splice (plan view)

Figure 15.4 - Cracking Due to Shrinkage

/

/Web

Segment ,iomt

'

~Tendons

'-

Crgcking at Blisrers

Cracks

~Segmenl jam!$

//

if'E•b

Cracking in

jci~l

~~----

Anchonge blister

£j-·-·".

------------- ------·

-~-----

---~---

,._-:-_;7Y

--~----

1~ndons

_L..

Grading behmd BlistQi.

Figure.J5.5- Cracking Near Blisters


8 of19

Prevent or mjnimiae this type of crackmg by limiting the size of tr1;1nsverse post -tensioning tendons fo unils of max. 4x0.6" strands placed on a min. 9u thick _._ __ deck

f

Cra.ck

Figure 15.6- Cracking at Transverse Post-Tensioning Anchorage

.1

15.2.7 Asymmetric Sections and Rotated Principal Axes Occasionally, it is necessary to employ segment shapes that are nnsymmetrical to a high degree. This may be expressed as a segment with greatly differing deck overhangs, or webs that are at different angles to vertical. While these features can be successfully integrated in the design, their effects on the segment's principal axes should not be overlooked. A rotation of the segment's principal axes can result in high bending stresses in the segment extremities, which would be overlooked if it were assumed that the axes were parallel to the bridge deck.

15.2.8 Shear Distribution of Multiple Webs With a typical single-cell box girder, it is relatively straightforward to determine the distribution of shear and torsion between the webs from the basic section properties. However, for sections with three or more webs, predicting the distribution of shear and torsion loads is more comple 15. A detailed analysis of the section, possibly through finite element modeling, is recommended to determine the actual portion of the total shear carried by each web.

15.2.9 Shear Lag The phrase "shear lag" is sometimes used to refer to different phenomena. In this case, it relates to the distance over which post-tensioning tendons can be considered effective. Because tendon anchorages are highly concentrated loads, it can take some distance along the axis of the tendon before the load can be considered effective across the full cross section. This is particularly trne for very wide superstrnctures with widely spaced webs. The problem can be most pronounced during constrnction in balanced cantilever, when the critical section for bending stresses may be located near the tip of the cantilever, and the tendon forces are not well distributed.

\J Chapter 15. 0 - Lessons Learned

9 ofl9

This can be mitigated by several methods. An effort can be made to distribute the tendon forces across the section, possibly by adding smaller anchors near the segment wing tips. Alternatively, an explicit calculation of the distribution ofloads into the superstructure can be performed, as is frequently the case in cable-stayed superstructures. During construction, it is possible to combat the problem by specifying a lower allowable stress in segment joints, or requiring a minimum compression at the joints when the stresses are calculated by conventional methods.

15.2.10 Combination of Transverse Bending and Shear Shear demand is generally the primary consideration in the design of the webs. However, the role of.local transverse bending should not be overlooked. Local loads on the top flange can create significant bending moments in the webs, which is resisted by the same vertical stirrups used to resist shear. While it can be very difficult to expressly design the web for a concomitant set of loads for both shear and transverse bending, both J. Muller(J) and C. Menn(4) have developed methods for combining the two effects in practice.

15.2.11 Built-in Loads For an inexperienced designer, it can be easy to overlook the importance of including the effects of the construction sequence. For many types of construction, the construction sequence has little effect on the design loading. Segmental construction, for any type of structure other than simple spans, sees a significant impact from loads built in during construction. These effects are particularly pronounced in balanced cantilever structures. A corollary to this is the effect of secondary post-tensioning forces. These are the forces caused by restraining support conditions when the tendons are stressed. The state of the structure when the tendons

are stressed determines the magnitude of the secondary post-tensioning forces, which can be significant.

15.2.12 Tendon Losses Internal post-tensioning ducts for segmental bridges are generally installed in numerous short lengths, no more than the length of a segment. This raises the possibility of additional small deviations at segment joints that would not be present in conventional post-tensioning. The magnitude of these deviations will vary with the quality of the workmanship in the precast yard, often within the same project (J. Muller C'i). It is important that appropriate values for friction and wobble are chosen by the designer. It is also important that any requirements for provisional or future tendons are incorporated in the design, so that unexpectedly high losses can be mitigated during construction.

15.2.13 Bottom Slab Drainage Detail The typical use of small number of I y, inch diameter drain holes in bottom slabs has often proved to be inadequate to insure drainage, as illustrated by Figure 15.7.

Figure 15.7- Ponding of Water in Bottom Slab ofSegmental Bridge Chapter 15. 0- Lessons Learned

. __) 10 of 19

The use of a more generous number of3 inch diameter drain holes, reinforced with spirals, and provided with wire covers to prevent bird intrusion into the box is recommended. Water depths covering external ducts have been reported, which resulted in some corrosion in tendons.

15.2.141nspection Access Design of segmental box girder bridges with inadequate inspection access, such as shown in Figure 15.8, is unacceptable.

Figure 15.8- Jnadequate Jnspection Access


11 of 19

15.3.0 Construction Lessons Learned 15.3.1 General Construction problems are, in general, the responsibility of the Contractor. However, Contractors usually assign responsibility for various aspects of the construction process to the Construction Engineer. None the less, the ultimate responsibility for resolution of construction problems rests with the Contractor. For this reason, all construction problems, or "lesson learned" discussed in the following sections have been compiled under the heading of "Construction Lessons Learned".

15.3.2 Equipment Requirements The Contractor's bid for a project is complex and dependent on many factors. The overall rate of production in erection or casting of segments compatible with the project time frame is a function of the amount of erection equipment available. The cost of erection equipment significaotly impacts the cost to build the project. There have been a number of segmental projects in recent years where it became necessary to add erection equipment during the construction

process to finish the job by the project completion date. While this issue does not generally impact the quality of the completed project, it does impact the commercial viability of segmental construction from the Contractor's perspective, and it represents a "lesson learned" in that context.

15.3.3 Construction Loads Detailed requirements related to construction loads for segmental bridges are presented in Article 5.14.2.3.2 of the AASHTO LRFD Bridge Design Specifications (1). These requirements, which are not included in the specifications for any other type of bridge construction, reflect the realities that construction loadings may control the design of various aspects or components of segmental bridges. The following is ao excerpt from the commentary to Article 5.14.2.3.2: "Construction loads comprise all loadings arising from the Designer's anticipated system of temporary supporting works and/or special erection equipment to be used in accordance with the assumed construction sequence and schedule. Construction loads and conditions frequently detennine section dimensions and reinforcing and/or prestressing requirements in segmentally constructed bridges. It is important that the Designer show these assumed conditions in the contract documents. These provisions are not meant to be limitations on the Contractor as to the means that may be used for construction. Controls are essential to prevent damage to the structure during construction and to ensure adequacy of the completed structure. It is also essential for the bidders to be able to determine if their equipment and proposed construction methods can be used without modifying the design or the equipment. " Since there have been some notable construction failures due to overloads, it is essential that the Contractor

determine precisely the weight of the erection equipment (particularly erection gantrys) aod other loadings, with respect to the assumed loadings in the contract documents.


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-)

15.3.4 Truss Stability Structures that are erected with an erection gantry will often see their greatest demand during the erection phase. It is essential that the procedures in the "User's Manual" preceded by the gantry supplier be strictly followed in use of the gantry. The loads imparted by an erection gantry can be very significant, and the details of the erection gantry support are critical to the performance of the gantry I structure system. One aspect of this system that is sometimes overlooked is the stability of the columns when loaded by the gantry. This is of particular importance when the gantry includes a "pendular leg", or a support that is pinned at the top and bottom, and carries no moment. This type of connection can lead to a highly unstable system for tall or flexible colunms. The difficulty arises when the loading from the gantry causes a longitudinal displacement in the colunm as shown in Figure 15.9. This, in tum, inclines the pinned leg, so that an additional shear is applied to the column. In the worst case, this shear causes increasingly large · deflections, until the entire system becomes unstable. This potential failure mode should be at the forefront of the construction engineer's consideration whenever this type of truss support is used. Full consideration should be given to potential sources of flexibility, including but not limited to foundation stiffuess and potential cracking of the colunm. Furthermore, the possibility should be evaluated even when the initial loading is anticipated to cause no displacement (i.e., loading at the center of the colunm), as small placement tolerances can lead to significant displacements for flexible columns. If discovered, this problem can be mitigated by altering the support conditions of the truss, or by bracing the colunms against longitudinal movement by mobilizing adjacent structures.

~-~~'~~"'" Eccentricity

Causes Secondary Shear

Figure 15.9- Gantry Support Instability


13 of 19

15.3.5 Bearing of Truss Supports When erecting segments with an erection gantry, the amount of space on the column cap for the truss supports can be limited. It is not uncommon for space considerations to drive the truss supports up to, and even hooked over the edge of a column cap. In these situations, it is very important to investigate the bearing capacity in the region surrounding the supports. In the worst case, a local shear failure can lead to loss of support for the truss. A milder concern is significant spalling ofthe pier cap, which can lead to costly repairs. This can sometimes be mitigated by stressing the supports against the pier cap through temporary sleeves, or by increasing the local reinforcement above what is shown in the design plans.

15.3.6 Warping Under Concentrated Loads Erection equipment often places high concentrated loads on the structure. While it is good practice to locate these loads above a rigid point, such as directly above a web, there are secondary effects that must be accounted for. High local loads can lead to warping of a box girder section, creating bending in the flanges. These moments should be calculated and accounted for whenever concentrated loads are applied unsymetrically to a box section.

15.3.7 Out-of-Balance Moments As discussed in previous chapters, various permanent and temporary details have been used to accommodate out-of-balance moments during construction. Of these alternatives, supports adjacent to

piers directly from the superstructure to footings do not induce any moments in piers. On the other hand, pier brackets do induce forces and moments in piers due to out of balance loads. Post-Tensioning tendons

from the superstructure to the footing have been used to support our-of-balance moments successfully, but are more flexible from the stand point oflimiting cantilever deflections.

15.3.8 Alignment and Geometry Problems Alignment and geometry problems have occurred on U.S. projects built in the early 1980's (see Figure 15.10), as well as in recent projects. Various proprietary and commercially available computer programs are now used to calculate alignment and geometry control. Even using, these resources,

significant and costly errors still occur. Global graphical plots of aligmnent and elevation control computer output are necessary to disclose numerical errors that may be overlooked. Additional quality control both during segment production and in erection is recommended as follows:

casting curves and geometry control procedure must be meticulously reviewed and double checked geometry control readings and set up calculations must be independently checked

the position of the instrument, target and form bulkhead, which are all supposed to be at fiXed positions, should be checked frequently using independent bench marks erection elevations and horizontal alignment controls should be provided for use during erection to check whether or not the correct alignment will be obtained.

Chapter 15. 0- Lessons Learned

14 of 19

Figure 15.10 - Closure Error between Cantilever Arms - 1980 r•J

15.3.9 Geometry Control in Gore Regions Gore regions are those areas where the roadway width varies significantly. This can sometimes be achieved by varying the length of the overhang, but there are instances where this is not sufficient. In these cases, the distance between webs may vary within a given span or casting set. When the separation between the webs varies, it is a good idea to vary the position of the survey markers to remain near the webs, so that tbey remain at a vertically rigid point. This can lead to a confusing set of casting coordinates, which are generally set to accommodate a fixed offset. Good coordination between the construction engineer and the casting yard survey team is critical in these cases to avoid casting errors.

15.3.10 Fit of Match Cast Segments In general, match cast segments fit perfectly during erection. However, if the match cast surfaces are changed after they were taken apart, they will not match. Such changes may result from: excessive sandblasting repair ofsurface defects (for example a broken shear key) epoxy grouted cracks Repair of surface defects should generally be delayed until after segment erection in order to avoid more damage to the joint.

15.3.11 Steam Curing and Warping Stearn curing in the casting yard can be an effective method for gaining high early strength. However, when done improperly, it can lead to fit-up problems during erection. If the steam is only applied to the wet-cast segment, the match-cast segment will see a temperature differential. The match-cast segment will curve during curing, which will be built into the wet-cast segment. However, when the steam is removed, the match-cast segment will revert to its original shape, while the curvature will remain in the wet-cast

segment. A comprehensive study of segment warping was conducted at the University of Texas at Austin(?) This study indicates that warping of segments will not be a problem when the width/length (W/L) ratio of the segment is less than 6. Procedures are recommended in the study when theW/Lis greater than 6. Applying the steam to both segments in their entirety will reduce the curvature.


15 of 19

15.3.12 Short Tendon Elongations Segmental construction, and particularly balanced cantilever construction often includes stressing tendons that are significantly shorter than typical applications. Tendons as short as I Om (30') are not uncommon. With tendons this short, elongation measurements can be strongly affected by the stressing procedures. Typically, tendons are stressed and re-sealed at a relatively low level before being stressed to their fmal values. For tendons whose fmal elongations are low, this re-seating can account for a measurable loss in stress, which must be accounted for in the secondary pull. Failure to do so will result in readings that consistently indicate the tendons have been overstressed.

15.3.13 Tendon Blockages To avoid or clear blockages prior to or during tendon installation, the following procedures are recommended: Use mandrels during casting to insure alignment of all ducts at joints. Temporary sealing of empty ducts is required to prevent debris from entering the ducts prior to tendon installation. This is even more important for vertical ducts. Swab all ducts immediately following segment erection to eliminate blockages due to epoxy squeezed into the joint. Alternatively, duct couplers will serve this purpose. Plastic ducts in footings have collapsed due to hydrostatic pressure from concrete. Concrete coring equipment was used to create new openings for tendon placement.

Locate the blockage location, and chip into the duct to remove the blockage. In event installation of one or more tendons is not possible, utilize alternative provisional ducts required by

the specifications for tendon installation.

15.3.14 Tendon Pop-Out As previously discussed, prestressing tendons exert outward pressures in areas where they are curved or kinked. In case the curvature is by design, the designer will provide reinforcing to contain the tendon. However, mistakes during construction can cause tendon pop-out. Figure 15.11 shows a slab which

contains a tendon which is supposed to be straight. However, due to insufficient support the tendon sagged in between the joints, thus creating a possibility for tendon pop-out, delaminations or bending cracks. Figure 15.12 shows two curved tendons at a diaphragm one over the other. When there is adequate distance between the tendons, a large radius of curvature, and properly compacted concrete in-between the

ducts, no problems usually develop. However, during construction both the distance as well as the concrete quality between the ducts may be less then intended. As a consequence, duct "b" can be pressed into duct "a," spalling the concrete and causing a problem with the stressing of the tendon in duct "a."


16 of 19

'r

'

cracks

.!1---r-.1-" ~ I ] F

I

J\ I

Goint ;;ack spa/lin11

Delamins.tion

/

l

):

I

j

'

FII'Hl Imprintof duct

Original

position of t.endon

Position of tendon ttffcr fai/w·e

Figure /5.11 -Effects ofMisalignment of Tendon Ducts

Manlw/e -

-·

C1·oss Girder Eleva lion

Figure 15.12- Curvature Pressure Exerted by Tendons

Chapter 15. 0- Lessons Learned

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15.3.15 Epoxy Not Setting This has occurred on a number of projects. The cause has usually been traced back to careless mixing of the two components. Other causes, however, are possible. The consequence of soft epoxy is that the shear keys will have to transfer the entire design shear from one segment to the next. Normally the shear keys are not designed for this, and, in the event soft epoxy is noted, an engineering check must be carried out. In the top slab there are normally only a few keys which should prevent vertical displacement ofthe joint faces in respect of each other, but, on the other hand, there may be a lot of tendons which act as dowels. Each case will have different circumstances. The following procedures are recommended to avoid epoxy not setting or to evaluate the significance of epoxy not setting when it occurs in isolated instances. I)

Good quality control on the mixing. It helps to color the hardener differently from the resin so that proper mixing can be checked visually.

2)

After soft epoxy has been noted, the cause established, and an engineering review indicates that keys across the joint are adequate (which they may well be), no further structural repair is required.

3)

The material in the joint should be tested in order to find out if there may be a problem with the durability.

15.3.16 Freezing of Water in Ducts and Recess Pockets In spite of the common knowledge of the expansion effect of water when it freezes, many projects show the signs of neglect to take necessary precautions, as follows:

I)

Grout tendons and recess pockets, if possible, before the onset of frost. Note that grout can itself freeze and that it does not help to grout when it freezes or at low temperatures.

2)

If certain tendons and/or anchor pockets cannot be grouted, they must be emptied of water by: a. b.

3)

Providing drains. If drains were provided, check that they function, Displacing the water with compressed air. Note that high air pressure can itself be problem.

If ducts are to be left ungrouted for a long period of time, temporary corrosion protection of the tendon must be provided.

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15.4.0

References

(1)

AASHTO LRFD Bridge Design Specification, American Association of State Highway and Transportation Officials, Washington, D.C., Fourth Edition, 2007.

(2)

AASHTO LRFD Bridge Construction Specification, American Association of State Highway and Transportation Officials, Washington, D.C., Second Edition, 2004.

(3)

Muller, Jean M. and Podolny, Walter "Construction and Design of Prestressed Concrete Segmental Bridges" John Wiley & Sons, 1982.

(4)

Menn, C., "Prestressed Concrete Bridges.

(5)

Muller, Jean M., "25 Years of Concrete Segmental Bridges Survey of Behavior and Maintenance Costs", J. Muller International, 1990.

(6)

Controlling Twist in Precast Segmental Concrete Bridges, Breen, John E., PCI Journal, V. 30, No. 4, July- August 1985, pp. 86-111.

(7)

"Temperature Induced Deformations in Match Cast Segments", Roberts-Wollmann, Carin L., Breen, John E., and Krager, Michael E., PCI Journal, July- August 1995.

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TABLE OF CONTENTS )

CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES

CHAPTER 16.0 CONSTRUCTION ENGINEERING & INSPECTION (CEI) OF SEGMENTAL CONSTRUCTION

16.0

Project Site Roles

2

16.1

Motivation of Stakeholders

3

16.2

CEI Early Involvement

4

16.3

Remote Precast Yard

4

16.4

Preconstruction Conference

4

16.5

Engineering Submittals, Shop Drawings, RFis

4

16.6

Technical Workshops I Submittals I Format

5

16.7

Critical Issues early on at Precast Yard

5

16.8

Concrete Mix Designs

5

16.9

Casting Yard Quality Control/ Geometry Control

5

16.10

Review of Erection Procedures

6

16.11

Confirmation of Erection Procedures

6

16.12

Post Tensioning and Grouting

6

16.13

Bearings, Expansion Joints and Seismic Devices

7

16.14

Highway vs. Rail Bridges

7

16.15

Record Keeping I As-Builts

7

16.16

Safety

7

16.17

Environmental Issues

8

16.18

Claims and Changes

8

16.19

Successful Project Ingredients

8

16.20

Summary

9

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16.0 Project Site Roles Before discussing the role of the CEI Consultant, it is very important to understand the roles of each of the stakeholders involved during construction. Clearly defining each role helps avoid the risks associated with assuming the responsibilities of another party and the resulting miscommunication.

The primary roles defined here are: • The Owner • The Contractor • The Contractor's Engineer • The CEI Inspection Team The Owner - The Owner is often not present on-site daily and has limited involvement until issues escalate to a level requiring his attention. The Owner relies on the CEI team to administer the project and to keep the Owner informed of issues as they arise. The Owner often receives technical advice from sources outside the Owner's organization; including, but not limited to the

FHWA, the Engineer of Record (EOR), the CEI team and perhaps on occasion from additional technical review consultants.

Regardless of the input, the Owner is the ultimate decision maker. The Owner must weigh and evaluate the technical merits of the advice of these sources together with their experience and expertise to arrive at a decision that is in the best interest of the Owner. This decision process may

include factors other than those that are purely technical in nature. The Contractor - The Contractor has the role with the most risk. While most engineers and inspectors claim to understand the Contractor's risk, many have no real grasp of its true potential.

With one bad decision on one project, the Contractor can put his firm out of business. The Contractor's goal is to build the project in reasonable conformity with the plans, specifications and special provisions provided by the Owner while maximizing his potential for profit. As nothing is assured, Contractors try to have a cushion to offset the unknown problems that will arise. Successful Contractors usually adopt "the glass is half empty and I think it has a slow leak" approach. The Contractor's role also includes managing his workers; dealing with suppliers; as

well as interfacing with the CEI team and Owner. Often the CEI team focuses only on the technical aspects of an issue and does not realize that the Contractor must weigh the technical against many other aspects as well.

The Contractor's Engineer- The Contractor's Engineer role is strictly defined by his contractual agreement with the Contractor, which outlines the specific tasks he is to perform. He bases his submittals and decisions on his experience, which might be very extensive.

He provides the

Contractor with specific engineering and technical advice. This input might not agree with the EOR's or Owner's engineering opinion but the Contractor will rely on it.

The CEI Team - It is the responsibility of the CEI Team to administer, monitor, and inspect the Construction Contract such that the project is constructed in reasonable conformity with the plans, specifications, and special provisions developed for the project. The CEI team therefore needs to coordinate the interests of the Owner, requirements of the Designer, the work of the Contractor, the submittals of the Contractor's Engineer and the issues and concerns of multiple jurisdictions,

utility owners and abutters. The CEI team's ultimate objective is to ensure that the Owner gets what he contracted for as indicated in the Contract documents, all regulations and permits are

adhered to, the project gets completed on schedule, the quality of the work meets or exceeds industry standards, Contractor payments are processed timely and changes are promptly and equitably addressed. The CEI Team is placed on the project to make decisions and to facilitate the Chapter I 6. 0- Construction Engineering & Inspection of Segmental Construction

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construction process and is not 1here to simply escalate issues up 1he ladder to the Owner for resolution. Some issues require escalation, however many more can be resolved at the project level. The CEI team's role is also to provide validation of1he design assumptions; 1hat is key, and 1he tasks that 1he CEI team performs (surveys, material testing, etc) are merely an aspect of 1he validation process. The full roles and responsibilities of 1he CEI team are more 1han can be addressed in this chapter. The intent of the following guidelines is to identify for consideration those that may be particularly important to consider in segmental construction.

16.1 Motivation of Stakeholders To be successful the CEI Team must also understand what motivates each of the parties. Conflicts arise when one stakeholder's proposal for resolution clashes with another's project incentives. Should the CEI team not understand the Contractor's incentives, issues may go unresolved and generate ill will. Some key motivations of each party are listed below. The Owner wants a quality project, completed on-time and within budget. He must represent and be accountable to 1he public. He must also answer to levels of government above him. His decisions will be challenged by 1he public or by oilier governmental levels therefore he must have justification for these decisions. One State Construction Engineer summarized it best when he remarked, "it is very easy to say no and let the issue be decided at a higher level, but a good DOT person will make a decision 1hat best reflects 1he overall good for the project." Willi human nature, it takes a strong person to make 1he final call on issues knowing that they always stand 1he chance of being second-guessed in the future. The Contractor's motivations are related to the fact that construction is a business and no one is in business wi1hout the goal of making money. This does not make 1hem evil or greedy, just good businessmen. Contrary to the opinions of some, Contractors by in large want to provide a quality work product. A large motivator for Contractors is the control of their own destiny. The potential to make a profit is influenced by so many factors outside 1he Contractor's control (wea1her, material availability, review time, etc.) that it is imperative that they control as many other aspects of the work as possible. Another motivator for Contractors is pride in their work plan. Often the work plan is submitted and 1hen 1he CEI team, 1he EOR or 1he Owner critique aspects of it that do not conform to their preconceived ideas of how the work should progress. The submitted work plan represents the Contractor's best me1hod based upon all of his knowledge and information. Any critique or challenge of 1he work plan can be viewed by 1he Contractor as a critique of him. The Contractor's Engineer is often overlooked. It is often assumed that the Contractor's Engineer has identical motivations to 1he EOR and Owner and therefore will spend unlimited amounts of time on an issue. The Contractor's Engineer wants and deserves to make a profit. He is engaged to perform a specific set of tasks. If he is required to perform these tasks multiple times, he is often not compensated for the extra work. Furthermore he is often under a time constraint imposed by 1he Contractor and as a result does not have the luxury to perform detailed, refined analyses to engineer an element. He will therefore rely on solid assumptions and proceed; because a conservative design done on time is more important than refined set of calculations that addresses every possible load case. The Contractor's Engineer does not get paid to revise work, but often the EOR, or reviewer, gets paid for reviews of revisions. This costs the Contractor's Engineer and generates revenue for the reviewer and has the potential to generate conflict. The CEI team and Owner should monitor the number of resubmittals required, and the reasons for them, to reduce this potential.

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16.2 CEI Early Involvement Segmental bridge construction continues to increase in popularity with the proliferation of experience and the recognition of the many benefits the construction method has to offer. However segmental bridge construction does pose certain challenges that require clear understanding to be addressed efficiently, effectively, and economically. Information is provided in other chapters of this manual that address the applicability of the various construction techniques, as well as lessons learned from previous projects. It is important that the CEI Team play a proactive role in the planning and execution of the work weighing the benefits for all involved parties. Many Owners are recognizing the need for early involvement of the CEI Team during the design phase by requesting constructability or bidability reviews of the contract documents during pre-bid phases. The CEI can also provide input and advice to the Owner with regard to contractor pre-qualification for complex projects, assist with pre-bid Q/A, participate in the preconstruction meeting and assist with bid review and analysis.

16.3 Remote Precast Yard Often the precast facility and the jobsite can be quite far apart. This may he due to the Contractor's choice to use an existing precaster that he may have worked with previously, or one that offers cost benefits based on prevailing local wages, or perhaps because there is no place nearby to set up a casting facility. In these situations the CEI team will need to provide inspection personnel to oversee the precasting operations and a separate group overseeing substructure and erection operations at the project site. Owners need to consider all likely possibilities on where and how the Contractor might want to handle his precast operations when setting up the CEI contract and provide flexibility in the event that the Contractor elects to do something other than what was

assumed.

16. 4 Preconstruction Conference The CEI Team leader will typically chair the pre-construction conference and will use this opportunity to introduce the parties to the contract, to each other and to review some early action items that must be completed before work can get under way. Bringing the CEI team on board during the pre-bid phase allows them to establish an early relationship with each of the parties, to understand the concerns of each (as noted in 16.2) and to develop strategies to address these concerns when construction gets under way. The preconstruction meeting is also an excellent time to discuss early action items and activities, associated submittals and to establish a program for technical workshops to get the engineering work underway.

16.5 Engineering Submittals, Shop Drawings, RFis A key role of the CEI Team will be in the handling and review of submittals and Requests for Information (RFis). Some RF!s can be addressed directly by the CEI team while others will require input and response from the EOR or Owner. It is recommended for large or complex projects that a representative from the EOR work in the CEI team field office alongside the CEI Team with direct access to the design office to be able to assist with technical matters and provide quick responses on issues that will inevitably arise. This arrangement provides Owners with the benefits of an independent CEI team along with the technical support of the designer readily available and has worked successfully on many projects.

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16.6 Technical Workshops I Submittals I Format The construction engineering and submittals required for a typical segmental project are considerable and Contractors will usually hire an engineering firm specializing in Construction Engineering to prepare erection details, staged construction calculations and shop drawings (see references to Contractor's Engineer above). To maintain schedule, it is important that these submittals get underway early following Notice to Proceed. One way to get these off to a good start is for the CEI team to set up a series of workshops involving the Owner, EOR, the Contractor and the Contractor's Engineer to review expectations for submittal content, format, PE stamp

requirements, submittal schedule and processing procedures. With advances in available equipment and software these procedures have changed considerably over recent years and

incorporating the latest technology to expedite the process is in the best interest of all concerned. The RJ:I process is a well established to address questions and or proposed changes and can similarly be streamlined by use of the latest technology. Some Owners may accept a completely paperless system while others will be open to the use of digital technology for expediting submittals and reviews while retaining hard copies for permanent records. Discussing and

resolving how these are to be handled early on will get everyone on the same page and into an efficient production mode.

16. 7 Critical Issues early on at Precast Yard The CEI Team overseeing casting yard operations should be involved at an early stage in the review of precast forms, and yard set up including quality control, concrete supply, rebar jigs and cage assembly, geometry control, segment handling, storage and transport. Once these major issues are underway, the CEI Team can work with the precaster to get into the details of segment casting with the objective of quickly getting into a production mode of one segment per form per day while meeting all of the contract requirements and tolerances. This is very important as it is quite normal and often essential to have a significant inventory of segments cast and waiting in storage before erection gets under way. The CEI will work with the Contractor to establish detailed checklists to be used for cage verification, PT duct layout, location of all embedments such as erection sleeves/anchor bolts or utility ducts, unistructs, etc. These are typically part of the contractor's quality control program which will vary from project to project based on specific contractual obligations.

16. 8 Concrete Mix Designs Concrete mix designs are another critical detail that must be addressed early, particularly when, as is often the case, trial mixes may have to be established, tested and approved before precasting operations can get underway. The CEI Team needs to work with the precaster, the Contractor, the testing lab and the Owner to coordinate testing and acceptance of trial mixes. These tests can be very time consuming and can quickly become critical path if one or more trial mixes fail to meet all requirements. Required contract testing for mix approval must be consistent with the contract schedule and the contractor's casting and erection schedule program.

16. 9 Casting Yard Quality Control/ Geometry Control Once precasting begins the CEI team will typically work closely with the Contractors personnel on geometry control. As referenced in Chapter 13, it is strongly recommended that two independent survey checks be made for as-cast geometry set-ups and these be checked by at least two independent methods preferably including one graphical method. The chances of catching a survey error, sign reversal or transposing problem are less likely to occur with two independent

)

survey and data reduction analysis system checks. In addition to the traditional geometry control survey for match casting it is very important that each segment be thoroughly checked after casting for dimensional tolerances and casting defects. It is easy to understand that repairs


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identified in the casting yard and corrected before shipment will be much less costly that the same repair that is identified during or just prior to erection when the erection of that segment is now on the critical path. Things to look for include, but are not limited to, a recheck on duct positions at the match cast joints, exit orientation angles for embedded PT ducts, broken shear keys, crushed or out of position PT ducts, bearing surfaces, embedded items etc. It is important that information is communicated from the casting yard to the jobsite for any repairs or corrections that need to be done after erection; such as repairs to match cast face.

If there are elements at the interface of substructure and superstructure that are dimensionally very tight, as-builts should be taken for coordination with the subsequent casting.

16.10 Review of Erection Procedures Erection procedures are typically a required submittal, regardless of the construction method proposed. An erection schematic is typically indicated on the Contract drawings and will usually note that such procedures are schematic only and complete details of the erection procedures and associated staged calculations are to be developed by the Contractor. This usually is contracted to a construction engineering consultant specializing in this type of work. The CEI Team should review these erection procedures from an engineering perspective and with regard to stability, equipment capacities, safety, schedule, and all other specific requirements of the contract. The

EOR will typically also review the procedures, but more often from a perspective of loading on the permanent, partially constructed structure to make sure that the permanent structure can support the erection loads and are consistent with those assumed during the design. Sometimes several iterations of these submittals may be required to reach approval of a package fulfilling all contract requirements. Load testing of the specialized equipment is typically specified and will be witnessed and approved by the CEI Team.

16.11 Confirmation of Erection Procedures Once these procedures and sequence are approved, it is imperative that the erection crews strictly follow the approved procedures and that any suggested changes to improve efficiency are thoroughly prepared and submitted and go through the same review process as the original submittal. Once erection commences, it is recommended that the Contractor's field engineer and a

member of CEI Team sign off on each step of the procedures. An example of an erection launching procedure signed by CEI Team and Contractor field engineer is included at the end of this chapter. This is especially important for erection gantries where failures of the past have most often been related to critical steps being missed or improperly carried out, usually during launching. The consequences of a gantry failure - serious injury or fatality, property damage, schedule impact and associated costs can be crippling on a project. Attention to details, staying with the approved sequence and insistence on competent supervision are critical. The minimum

qualifications of the Contractor's personnel operating these major pieces of equipment should be specified in the contract and strictly enforced.

16.12 Post Tensioning and Grouting The structural significance of post tensioning in precast segmental bridge construction as the primary reinforcing element of the bridge warrants special attention during installation, tensioning

and with the details of corrosion protection provided by grouting. The CEI Team must pay particular attention to ensure the applied forces are as per the design requirements by confirming jack calibrations, gauge pressures and reconciling elongations. Any inconsistencies must be

satisfactorily explained. These operations should be performed by trained Contractor personnel who understand the importance of the PT, and the associated QC required. Both the Contractor Chapter I 6. 0- Construction Engineering & Inspection of Segmental Construction

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and the CEI Team should keep detailed records of post tensioning and grouting and reconcile these routinely to make sure complete sets of data will be turned over to the Owner at the completion of the project. Examples of a stressing record and a grouting record are included at the end of this chapter.

16. 13 Bearings, Expansion Joints and Seismic Devices Bearings and expansion joints are two other elements of the bridge that must be installed correctly to ensure that the bridge will move as intended during its design life without distress. Bearings can be fixed or provide for movement in one of both directions and must be correctly oriented to allow for freedom in that direction. Both expansion joints and bearings are typically set to specific dimensions based on temperature at time of installation.

Sometimes these devices must work in harmony with seismic restainers/buffers and eac:;h element must be installed correctly and within specified tolerance if they are to work together. A thorough review of all related tolerances is recommended prior to precasting and substructure construction to make sure that all elements will be able to be installed correctly. The CEI team and Contractor should reach agreement early on procedures for setting and verifYing how this will be achieved as part of the Quality Control Program.

16.14 Highway vs. Rail bridges Segmental construction is now a well proven method for highway bridges. This method of construction is becoming popular as well for light rail construction. It is important that the specific demands each be fully understood and not assumed that what is good for one will work for the other. Light rail construction with direct fixation track requires tighter tolerances to be sure that rail plinths and rail installation will meet specified contract requirements. Recognition of the finer details early on will pay dividends later.

16.15 Record Keeping I As-Builts As with any CEI consultant contract, a very important element of the consultant role is ensuring adequate documentation is maintained during construction and turned over to the Owner at the end of the contract. This will usually be a combination of all records of construction including correspondence, submittals, RFis, daily reports, materials certificates, test reports, non conformance reports and how these were resolved, as-built installations and any deviations from design drawing, utility locations and details, product data, warranties, progress payments and Change order records. The administrative responsibilities of these contracts can quite onerous and Owners need to recognize the staffing required if the benefits of a competent CEI team are to be fully realized.

16.16 Safety The Contractor is responsible for overall site safety and for all persons and property on the site and will normally have one or more full time on-site safety representatives assigned to oversee the work and ensure compliance with all local and federal safety requirements. That being said, Owners and CEI consultants who have been involved in post accident investigations and the lengthy and costly litigation that can result from a serious accident fully understand the importance of a detailed and comprehensive accident prevention program. Attendance of the CEI team in Contractor toolbox meetings is strongly recommended particularly prior to the start of any new operation. The submittal of construction work plans and review by CM should address how the physical work will be performed including associated Job Hazard Analyses (JHAs) that must be reviewed and fully understood by the workforce. The Owner may provide or request the CEI team to include trained safety personnel specifically assigned to the Chapter I 6. 0- Construction Engineering & Inspection of Segmental Construction

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project that can conduct daily site inspections and be the go-to person on the Owner/CEI side with regard to safety issues. It is connnon practice for safety to be the frrst item of discussion at weekly or bi-weekly progress meetings and these are an excellent forum to address safety planning and or corrective actions. However the concept of"Safety is everyone's responsibility" is a good one for all of us to remember each and every day. This can be achieved by adoption of the philosophy that no one should walk by an unsafe act or condition without taking corrective action or bringing to the attention of the appropriate individuals who can.

16. 17 Environmental Issues Just as safety is everyone's concern so is environmental compliance. The construction industry in general has come far in recent years to address practices that were connnon not too long ago but are now generally considered unacceptable or illegal. Regulatory agencies can impose significant fines for non-compliance and Owners will suffer even more when they attempt to seek permits for future work if there is a history on non-compliance. The. CEI team must work with the Contractor to identify the environmentally sensitive issues, particularly when working over water or adjacent streams and wetlands. Preventative measures will include Best Management Practices for collection of sediments, water treatments systems for high PH, methods of disposal for grout concrete epoxy, styrofoam, etc. Owners need to consider whether to make environmental issues a separate bid item and if so perhaps to include a provisional sum to be billed against on Time and Material as the requirements of the regulatory agencies may be hard to gauge and may change during the course of the contract resulting in disputes over unanticipated costs.

16. 18 Claims and Changes Another key role of the CEI team is to handle claims and changes. Since precast structures can be fairly complex it is not unconnnon for related claims and changes to be quite complex too. Disputes can arise over issues of constructability and/or rebar and PT conflicts and the respective

responsibility of the designer and contractor. The CEI team should be capable of taking an active role in resolving these types of disputes which requires a good understanding of design principles, construction and industry practices and as well as dispute resolution procedures. It cannot be

understated that these issues are best resolved by the people in the field as they occur and a sincere effort by the parties to the Contract should be made to do that for the benefit of all concerned.

16. 19 Successful Project Ingredients Based on experience from past projects, there appear to be some key ingredients needed for a

successful project. The CEI Team needs to take the lead in ensuring that these key ingredients are in their project. These keys to success include: •

Teamwork - The Owner, Contractor, Designer and CEI Team must all be working for a

quality project that is built on-time and makes money for the Contractor. Many projects have "Formal Partnering" events every quarter and then have adversarial relations on the day-to-

day business of building the project. Teamwork or Partnering must be a large aspect of the day-to-day interaction between the parties on-site. Since the CEI team has the most daily interaction with the Contractor, they have the most opportunity to foster teamwork.


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•

Respect of other points of view - For the project to succeed, egos must be checked at the door. All too often, parties do not listen well to each other and refuse to acknowledge any other point of view besides their own. That does not work. The CEI team should take the lead in fostering good communication and understanding. They need to clearly state their or the Owner's understanding and then solicit the Contractor's understanding. Then, if there are any differences, all of the parties need to work together to come to a consensus decision that

best serves the project. •

Maximize project level decisions - The CEI team is placed on a project to administer it and this includes making appropriate project decisions. If decisions are not addressed at the lowest practical level, then the project suffers delays and usually claims result. The Contractor places personnel at the project with the authority to make decisions and if the Owner and CEI team also have on-site personnel with the authority and willingness to make decisions, then the project stands a great chance of being a success.

16. 20 Summary Quite simply, the CEI Team should be a part of the solution and not part of the problem. The CEI Team can affect the project success by their actions or inactions! Inaction is not representing the

best interest of the Owner. There is no place for adversarial attitudes on part of the CEI team. Further, it is imperative that the CEI team lead by example with a cooperative attitude. Also, when the Contractor sees that the CEI Team is working with them on a daily basis, then positive relationships result and the Contractor responds by working more with the CEI Team and Owner. If the CEI Team is helping the project succeed, then the Contractor makes money and the Owner gets the project he envisions. Everyone wins.

)

Each project starts with a sense of trepidation, since the project staff usually does not know each other well. If the CEI team shows a willing attitude every day, then the Contractor will soon reciprocate. Someone has to be the first to be cooperative and it is in the project's best interest if it is the CEI Team. Below is a list of some positive steps that the CEI Team should consider. While this list is not all encompassing, it helps set the framework for project success. •

Be consistently fair - There needs to be a realization that it is much harder to tighten the requirements once you have relaxed them. The project requirements should not vary from day to day or from inspector to inspector. The CEI team manager need to ensure

that there is uniform inspection. •

It is also important to explain your reasoning.

If something is important from an

inspection point of view, then the CEI team manager should explain the importance to everyone including the Contractor. This helps educate the work force and improve quality. •

There also needs to be a realization that there is interpretation to plans and specifications.

Often a Contractor has a different interpretation and it is the CEI team's role to help resolve differences between the different interpretations.

Sometimes the Contractor's

interpretation is different from the Owner's but may still be valid. By being an open minded thorough listener there is a much greater chance of resolving these differences

amicably and for the good of the project.


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•

The CEI Team should not expect perfection.

The CEI Team should focus the

specification tolerance on critical areas. For instance, the location tolerance for #4 reinforcing used for temperature cracking control is obviously not as critical as the

location of #8 shear reinforcing. •

Give the Contractor a "clean slate" everyday. The CEI Team can't have their judgment clouded by the past. Even ifthe Contractor is not being cooperative, the CEI Team has to judge each issue on its merits alone. This is very difficult but it is also extremely important.

•

Be Proactive - The CEI Tearn needs to organize and hold meetings in advance of any operation to ensure that all parties have the same understanding of the requirements. The earlier that these meetings can be held the better, to allow more time to react to any comments that arise.

•

The CEI team needs to share ideas with the Contractor that might help him and the project. This can be anything from alerting him to required submittals to a different way that another Contractor performed an operation. The CEI Team needs to identify issues before they impact the construction schedule.

•

The CEI team also needs to hold meetings well in advance of any major submittals. The goal is to develop clear consensus of requirements and acceptance criteria. If this occurs,

then resubmittals are minimized. •

Show respect to all Contractor personnel - The largest single mistake that a CEI team can make is in thinking that the Contractor is stupid, greedy or wants to do poor quality work. This is simply not true. It is also important to explain to the work force why certain aspects are more critical. For example conveying the importance of accurate positioning of confinement or bursting reinforcing behind post-tensioning. If the work force

understands the importance, then the quality will increase. If the work force thinks that the inspector is merely being a "bad cop" who is beating them with the specifications, then quality will suffer. •

Finally, the Contractor's Engineer should be treated with the "Golden Rule". They should be treated like the CEI Team would like to be treated. There should be no resubmittals for petty reasons.

•

Provide Technical advice to the Owner- The CEI team should always hold meetings with the Owner in advance of any meetings with the Contractor. At these meetings the CEI Team and others can openly share information with the Owner so that he has the most information to make decisions for the project on technical issues. This might not be in line with recommendations from some advisors, but once the Owner has made the decision, then the CEI Team needs to present this to the Contractor and maintain a constant message. The Owner makes his decision based on many factors and, for the best

interest of the project, the CEI Team needs to support this decision once it is made. As part of the discussions with the Owner, the CEI Team needs to realize that the Contractor and his Engineer also have experience and expertise. It is very easy to simply agree with the Owner but it is in their best interest to give an honest opinion. Sometimes

the advisor needs to play "the Devil's advocate".

The CEI Team and all technical

advisors need to give honest opinion and, where possible, cite examples from similar work elsewhere. Without good reason, no Owner wants to go outside the norm of industry practice. Also the Owner will not want to make a decision based on incomplete information.


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Motivating the Contractor - As discussed above, all the parties have motivators. For a Contractor it is much easier to get results using the "carrot" rather than the "stick". If the CEI Team can show the Contractor why his actions are costing him money, he will change his actions. The CEI Team should make "early mistakes" costly within the allowances of the project scope, so that the Contractor will strive to avoid them. If "early mistakes" are treated too leniently, then there is no incentive to avoid them. Once he has established processes in place, they are difficult to change so it is important to get quality incorporated early. A very true adage is that it is always cheaper to do it right the first time.

•

Do not surprise anyone- This seems obvious but it often occurs. If there needs to be a strong letter to the Contractor about an issue, the CEI T earn should have already had meetings with the Contractor about that issue. If it arose suddenly, then the CEI team needs to have a face-to-face meeting with the Contractor and discuss the contents of the letter. If·anyone gets a strongly worded letter "out of the blue", then relations sour quickly and the project suffers.

•

Stoppage of work should be the last resort - The CEI Team has many tools at their disposal to ensure quality and compliance. If an issue escalates to the point that the project will be stopped, then things have gone very wrong. If the project is stopped then it is likely that the project will not finish on time and there will be claims. This is sometimes necessary but usually it is not in the "Best interest of the Owner".

The CEI Team is in a unique position between the Owner and the Contractor to help the project achieve success. The CEI Team needs to maintain professional distance from the Contractor but also take positive

)

actions to help the project. The CEI Team on successful projects is "part of the solution". The CEI staff is engaged by the Owner and the EOR to help facilitate the construction process though coordination and communication and not to be a "bad cop" that documents daily infractions. All Owners are urged to ensure that the CEI staff who are present on-site be structured so that they help the project get completed with quality, within budget and on time .

. _)' ·Chapter 16. 0- Construction Engineering & Inspection of Segmental Construction

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TABLE OF CONTENTS CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 17.0 CONSTRUCTION INSPECTION GUIDELINES FOR SEGMENTAL CONCRETE BRIDGES

17.1 17.1.1 17.1.2 17.2 17.3 17.4 17.5

Recommended Practice for Initial Inspection of Forms Form Dimensions and Tolerances Form Operation Recommended Practice for Daily Inspection of Forms Recommended Practice for Inspection of Cut and Bent Rebar Recommended Practice for Inspection of Rebar Cages Recommended Practice for the Initial Inspection and Storage of PostTensioning Hardware 17.6 Recommended Practice for Inspection of Post-Tensioning Hardware In the Reinforcement Cage Recommended Practice for Resolution of Rebar Conflicts 17.7 Recommended Practice for Inspecting Post-Tensioning Hardware 17.8 in the Form 17.9 Recommended Practice for Inspection of the Setting of Matchcast Segments 17.9.1 On-Site Hardware 17.9.2 Measuring Instruments 17.9.3 Observations in the Casting Cell 17.10 Recommended Practice for Concreting Segments 17.11 Recommended Practice for Inspection of Curing of Segments 17.12 Recommended Practice for Inspection of Stripping Forms and Bond Breaking 17.13 Recommended Practice for Inspection of Segment Handling in the Casting Yard 17.14 Recommended Practice for Inspection of Repairs Made to Segments 17.15 Recommended Practice for Inspection of Segment Storage 17.16 Recommended Practice for Inspection of Segments for Payment 17.17 Recommended Practice for Inspection of Segment Transportation 17.18 Recommended Practice for Inspection of Erection Equipment 17.19 Recommended Practice for Inspection of Falsework 17.20 Recommended Practice for the Inspection of Epoxy Joints 17.21 Recommended Practice for Tendon Stressing 17.22 Recommended Practice for Inspection of Grouting 17.23 Recommended Practice for Inspection of Cast-in-Place Segmental Structures

Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

3 3 5 7" 8 11 15 17 18 20 21 21 22 23 26 28 29 30 31 33 34 35 36 37 38 40 40 40

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TABLE AND FIGURES CONSTRUCTION PRACTICES HANDBOOK FOR CONCRETE SEGMENTAL AND CABLE-SUPPORTED BRIDGES CHAPTER 17.0 CONSTRUCTION INSPECTION GUIDELINES FOR SEGMENTAL CONCRETE BRIDGES

Table17.1 Table 17.2 Table 17.1

Completed Segment Tolerance for Segmental Box Girder Bridge Construction Minimum LAP Splice Dimensions for High Strength Concrete Recommendations Concerning Moving or Cutting Rebar

Figure 17.1 Figure 17.2 Figure 17.3 Figure 17.4 Figure 17.5 Figure 17.6 Figure 17.7 Figure 17.8 Figure 17.9 Figure 17.10 Figure 17.11 Figure 17.12 Figure 17.13 Figure 17.14 Figure 17.15 Figure 17.16 Figure 17.17 Figure 17.18 Figure 17.19 Figure 17.20 Figure 17.21 Figure 17.22

Measurement of Form Adaption of Form to Section Changes Typical Requirements for Form Adjustments Standard Fabrication Cutting and Bending Tolerances Example of Poorly Bent Rebar Requirement for Tight Tolerances Jig for Fabrication of Rebar Cage Reinforcing Steel at Post-Tensioning Anchors Handling of Prefabricated Rebar Cage Typical Post-Tensioning Anchorages (Strand Systems) Plastic Ducts and Grout Vent Connection Aid for Solving Rebar Conflicts Tolerances on Anchor Placement Geometry Control - Reference Hardware and Axes Casting Cell Survey Control Arrangement Measuring Equipment Observations (After Casting) Three-Dimensional Geometry Control Data Sheet Casting Sequence for Regular Precast Segments Handling Segments Repair of Honeycombed Area Stacking Segments

4 13 19

3 5 6 9 10 10 12 14 14 16 16 18 20 21 22 23 24 25 27 30 32

33

··.)· -


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'

17.0 Construction Inspection Guidelines for Concrete Segmental Bridges 17.1 Recommended Practice for Initial Inspection of forms The purpose of the initial form inspection is to veruy that the form was mannfuctured and can be assembled in accordance with the approved form shop drawings, as well as inspection of the operation and maintenance of the form during the first few castings. During this process, it is recommended that inspections be made to verifY the suitability of the forms in reference to the points discussed in the following sections.

17.1.1 Form Dimensions and Tolerances Check the dimensions of the segment the form will produce (see Fig. 17.1) to confirm that the dimensions are within the tolerances listed in Table I.

Plumb

Level

---'"--''---'---~..LI.~Top of rail

-r ----~--

I

I ~----~-- -r I I 'I'- ....-1-- I I I 1_.. -1 1'- I I .j- ......1 I --1I 'lf- _.... I I I

~ Square

.

I

'i---I

-} ·

Use string tor Tolerance measurements

I ' - _,J

Inner form

Figure 17.1- Measurement of Form

·)·· ·~--


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Table 1 Completed segment tolerance for segmental box girder bridge construction. (To correlate tolerances, see sketches below.) Finished segment tolerances should not exceed the following: Overall depth of segment ± y, inch ± y, inch Length of match-cast segment (not cumulative) ±I 0.4 mm/m, ±I in. max. (±25 rom) ± Y, in. but not greater than + 2 in. per span Length of cast-in-place segment ±%in. (9.5 rom) Web thickness ±%in. (9.5 rom) Depth of bottom slab ±%in. (9.5 rom) Depth of top slab ± 1/16 in/ft (5.2. mm/m), ±% in. max (25 rom) Overall top slab width ± Y, in. (12.5 rom) Diaphragm thickness ± y, in. in I 0 ft ( 1.0 mm/m) Grade of form edge and soffit ± Y. in. (3.2 rom) Tendon hole location ± !4 in. (6.3 rom) Position of shear keys ± \> in. (6.3 rom), per 20ft. (2.0 mm/m), but Jess Deviation of segment ends from a plane in width than Y, in. (12.5 rom) or depth \> in. (6.3 rom) maximum Deviation of surface from a plane at any location measured with a I 0 ft. straight edge

Note! Shear .keys.no:t shown

SEGMENTAL BOX GIRDER

POSmO~OF~ SH~R KEVSLY-·-----l-1------wee

J -rr~------....~.+T-------------

.,. '-

KEY__....,

J.

OlAPHRAGM TtiiGKNES$

------~

LONGITUDINAL SECTION

i'· j Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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Dimensional checks are necessary at the bulkhead side and the matchcast side, as well as in between. Dimensions of the matchcast and bulkhead sides should be identical. Variations in dimensions at the two ends may result in mortar leakage, or require large forces on the "old" segment to close the form which may move the segment out of alignment. The form should be reassembled as required to revise and verify dimensions of the section for all variations in web and bottom slab dimensions (see Figure 17.2). Most balanced cantilever bridges require thickening of the bottom slab, and sometimes thickening of the webs near the pier. For this reason, forms may have to accommodate several section changes. Dimensional location of any items attached to the form to secure their position during casting of concrete, and requiring removal before shipping the forms should be noted.

·L-_ _

In sp:m.

)

Bottomslab thickening

Near pier

Figure 17.2- Adaption of Form to Section Changes

17.1.2

Form Operation The geometry control of precast segmental bridges is based on the assumptions that the soffit of the new segment is level and bulkhead face of the new segment is plumb or perpendicular to the soffit (see Figure 17 .I). This should be carefully checked using an instrument and, since the bulkhead could potentially move each time a segment is cast, should be checked for each new segment set up.

The "old" segment needs to be placed in a certain position in respect to the form (see Figure 17.3). After appropriate setting of the "old" segment, the position should be fine tuned to within a 1116 in. tolerance. Mechanisms such as hydraulic jacks or screw jacks are used to accomplish this adjustment. The position changes to be controlled by such mechanisms are: rotation in the horizontal plane, rotation in the vertical plane through the bridge centerline, and rotation in the vertical plane perpendicular to the bridge centerline. In addition, the "old" segment should be able to move in, and perpendicular to the direction of the bridge centerline. The seals between the various form panels themselves and between the form panels and the "old segment" must prevent mortar leakage from the fresh concrete. Such leakage affects both quality and appearance of the segments. The seals are a major feature of form design and, since they are usually flexible rubber or neoprene gaskets, they require regular cleaning and maintenance.

Checking of seals is a continuous task during production. Of particular importance is the seal between old segment and form panels, because the position of the old segment is not fixed and the seal and form must adapt to the old segment's rotated position. Any movement of the old segment during closing of the form will cause errors in the bridge alignment.

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Use of form oil as necessary to reduce adherence between the form and the segment, particularly in top slab overhangs. Bond between the vertical faces of the new and old segments is reduced by generous application of the specified bond-breaker, usually a mixture of soap and talcum powder. A procedure for bond breaking shall be shown on the segment shop drawings or described in the Construction Special Provisions to ensure that shear keys and the segment faces are not damaged during the process of breaking the bond between segments. Inspection of the forms during castiog of the initial segments should verify that the form allows for inspection of rebar, post tensioning duct and anchorages as well as other embedded items in the form. Such inspections mainly relate to clearances, post-tensioning anchor-duct aligmnent, and embedded item locations. The inspector should be able to enter the form for this inspection prior to closing the inner form. For concreting, it is important that the concrete can be brought to its final location without dropping from a great height and without having to move it with a vibrator. Special chutes, slides or openings in the top slab form are usually required to place the bottom slab concrete. For finishing of the deck, it is important that the top surface can be screeded by placing a screed over the "old" segment and the form bulkhead. The form design should minimize obstructions which interfere with the use of the screed. The initial inspection of form operation should verify that the form is provided with access ladders and safe working platforms with railings all around.

n

Qld

Uc:=:=:==l-se-'Jim"""'eH.,.,jt Ra!atfog

R'o!aUon In vertical plane

in boriznn!al plane

Adjust segment length

I

ii

J----1...---.-j\

I

I

\lr I

Rotation About Deck .4:

Figure 17.3- Typical Requirements for Form Adjustments

')· . .


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17.2 Recommended Practice for Daily Inspection of Forms The following daily inspections of forms are recommended: •

•

• • •

•

) •

VeriJY that the form is clean and that movable parts are oiled and greased as required. Because of the many mechanical parts used in the form, e.g. for collapsing the inner form and adjusting the position ofthe "old segment", hardened concrete spills, not properly and regularly cleaned, will make the form inoperable. Verify that seals are clean and flexible. Proper functioning of seals in preventing loss of mortar is essential to production of segments of acceptable quality. It is essential that seals be cleaned daily, and that any hardened concrete is removed. Seals are usually neoprene and are easily damaged. They should be repaired or replaced as necessary. Verify that the form oil approved for use on the project is applied. in accordance with the

manufacturer's instructions. Check to ensure that the form is adjusted correctly for the segment to be cast. This is particularly important whenever there is a change in bottom slab or web thickness or other section variation. Inspect to ensure that recesses, attachments for embedded items, and boles in the bulkhead are set up properly for casting the next segment. The ouly item that is sure to vary from segment to segment is the post-tensioning. This variation occurs in both cantilever post-tensioning and continuity post-tensioning. For this, anchor recesses may have to be removed or added. Holes for tendon ducts in the bulkhead must be closed or opened. It is very demanding and important that the contractor and inspector independently check the post-tensioning in each segment. !fan error is made here, the consequences are very serious. Check closure of the form around the bulkhead, between the bottom slab form and side form, and around the "old segmeuf'. Closing the form at bulkhead and at bottom slab form usually does not present great problems since bolts through the form can exert enough-clamping force to achieve the seal. Closure around the "old segment" where clamping through the form is not possible, is more problematic and this is where the effort should be concentrated. Check the temperature of the form immediately before casting concrete. The combination oflow slump concrete and forms heated by the sun to high temperatures may cause a condition where the water in the concrete evaporates as soon as the concrete contacts the form. This leads to an unsatisfactory surface condition. Forms should preferably be placed under cover from the weather. Alternatively, the form can be cooled with water prior to casting. Ifthis is done, excess water must be removed prior to concrete placement, e.g. with compressed oil-free air. Care must be taken in removing excess water not to remove the form oil.


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17.3 Recommended Practice for Inspection of Cut and Bent Rebar Comprehensive information on all aspects of reinforcing bar detailing is available in "Reinforcing Bar Detailing" Concrete Reinforcing Steel Institnte, 833 North Plum Grove Road, Schaumburg, Illinois, 60173. Topics of primary importance on this subject for segmental bridge construction are discussed below. • •

•

Ensure that the steel has passed all required tests and has been approved for nse on the project. This indicates that the quality and mill tolerances of the rebar are acceptable. VerifY that the steel has been properly tagged and that the tags show bar diameter, bar number and the segment it is intended for. This is the responsibility of the contractor, but should be checked occasionally by the inspector. Check reinforcement for cutting and bending tolerances, and reject any reinforcement not within tolerance.

Unless specified to the contrary, steel will be cut and bent in accordance with standard tolerances set by CRSI (Concrete Reinforcement Steel Institnte). These tolerances are as shown in Figure 17.4. For straight bars, only cutting tolerances apply. If important, a higher tolerance can be demanded at additional charge, or alternatively, a lap splice provided. For normal segmental design, the± I" cutting tolerance should be acceptable. Bends are made around pins which are designed in such a way that the steel is bent to the correct radius. The radius of bar bends is important and shonld be checked since bars Jose some quality at bends. If bent, the Joss of quality can be dramatic, especially in case of thicker bars (#6 and up). Bar bends are also important for the fit of bars. A badly bent bar may not function properly as demonstrated in Figure 17 .5. The location of bends is also very important as shown in Figure 17.6. The vertical bars shown rarely fit if bent in accordance with the standard tolerances. These bars should either be made in two sections, or be bent to tighter tolerances at additional cost •

Check epoxy coating in accordance with special provisions. Epoxy coating can be damaged during handling or by field cuttings. Corrosion will concentrate on uncoated areas. For this reason, damaged areas of the coating must be repaired.


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Length plus or minus 1"

e

j

.5)

1o-dimeDSian plus or minus

rl

«=,./d)

I0-dimeMion plUs or minus 1:j

H-plus or

!Binus o. az L. lor bar sizes

)

#8 Spiral or circular tie

~md

larger

Tie or stirrup 90{+)or{-)2.5'

tF==~·

....

I

~

.s E!

Figure 17.4- Standard Fabrication Cutting and Bending Tolerances

.) Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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Correct

Crack

Wrong Figure 17.5- Example ofPoorly Bent Rebar

tolentnce

1• standard

No tolerance problem

tolerance not suitable

l!Jierance Figure 17.6 -Requirement for Tight Tolerances


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17.4 Recommended Practice for Inspection of Rebar Cages At a production rate of one (I) segment per form per day, the rebar cage is on the critical path and most of the inspection should occor while the cage is on the template waiting to be placed in the form. The template is a wooden structure (see Fignre 17.7) which simulates the form and is used by steel workers to ensure that the cage will indeed fit the form. On some projects there will be many different segment types each of which will have a different cage. In order to match up cage and segment correctly, the contractor will have to design a good identification system. All cages should be tagged in accordance with this system. The inspector should identify the cage, verify the identification tag, and check to ensure that an approved shop drawing was used for making the cage. The cage should be inspected with reference to the items discussed below. a.

Segment dimensions. Inspection for segment dimensions, day to day, will be required on projects where segments have a lot of variation on the bottom slab, web thicknesses and length of the overhang. In this case, the template for making rebar cages must allow variable dimensions and these dimensions should be verified.

b.

Bar diameters. There is no tolerance on the use ofbar diameters. For example, #4 bars cannot be used instead of#5's and conversely. Aoy deviation in bar diameters should be checked with the Owner's Engineer

c.

Number and spacing ofbars. The spacing ofbars (center to center distance ofbars in the same mat) showo on the shop drawings should be within a normal tolerance of I". In some cases larger tolerances could be allowed; for example, when openings or embedded items prevent placement of a bar. Table 17.3 provides guidance to the inspector to judge the importance of accurate rebar placement. Whatever the case, the total number of bars showo in the shop drawings to be placed in a mat should always be present. Additional bars can usually be

accepted, at no additional cost, for the convenience of the contractor.

.

)

d.

Number of ties. Ties should generally be wire ties uuless the shop drawings indicate the use of weldable steel, in which case the cage may be sp
e.

Length oflap splices. The minimum length oflap splices is showo on the shop drawings. The minimum length should be verified in the cage. There is no tolerance on this minimum length, but lap splices may be longer than required. In case field splices are required, dimensions of minimum lap splices are provided in Table 17.2.

f.

Number of distance keepers. Guidelines for the number of support chairs for top mats provided in the standard specifications.

g.

Size of distance keepers. Size of distance keepers is most important since it determines the cover and therefore the durability of the concrete segment. In addition, it determines the

intended location of most structural reinforcement. In general, reinforcement is more effective as it is placed closer to the faces of beams and slabs, and the position is determined by the clear cover. The tolerance on cover is l/4 11 and this is the tolerance for the location of the rebar mat in respect of the outside and inside faces of the segment. This tolerance is not required for the joint face of the segment. Once the structure is erected, the joint faces will not come into contact with the atmosphere and cover on the joint faces will not have durability consequences. The cover of reinforcement from the joint faces is shown on the shop drawings. This is subject to the normal± I" tolerance for bar spacing .


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Special reinforcement is required at locations where segments need to be strengthened; for example, at pickup points, strutting supports, near openings (temporary or permanent manholes). Prestressing anchors also call for special reinforcement, such as spirals and hairpins (see Figure 17.7). Locations where tendons are strongly curved may also require special reinforcement. Dimensional integrity of a rebar cage mnst be maintained during transportation of the cage. For this purpose, the cage can be stiffened with a frame (see Figure 17.9). The rebar cage should be inspected for obstructions to the location of tendon ducts. See Figures 3.20 and 3.21 of the "Post-Tensioning Tendon Installation and Grouting Manna!" for guidelines on duct placement. Tendon ducts should be placed at their designated locations without cutting any rebar. Ducts should preferably be placed in the cage before it is placed into the form so that modifications to the reinforcement cage required to let ducts pass through can be made without loss of segment production. For instructions regarding field cutting and bending of reinforcement, see Section 17.7 "Recommended Practice for Solving Rebar Conflicts." The cage should be checked for damage to epoxy coating, and damage to the coating should be repaired.

Standard duct JocaUOn

ThiS Illustrates a .pops~.ble jig. Other types, inc.Juil),ng those for special segments might be n~cled. Sometimes partial figs and templates are more convenient, e.g. .for tpp s.lab rein!orcemt:nt

mat only. battom slitb

Soffits and

outside

surfaces

reirdorcement only. el.c.

Figure 17.7- Jig for Fabrication ofRebar Cage


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Table 17.2 -Minimum LAP Splice Dimensions for High Strength Concrete

Stnmlard'ReiltforcementChurt··For AA$HTO llsihg S,SOUPSI. OJne; & 60KSI Steil *1r'Top Tension hap Splice Bar#

Wi:leht

Arell

3

0<376

O.ll

Bat DJA. (iu} 315

4 5 6 7

M~S

Q20

{$00

1.043 1,$1)2

0.31

.62$ .750

r-Z"

Z.644

MO '0.79 UIO

.815 1.000 1..121!

2' i" 2' -9"

3?--6"

4'-6"

1.27

1.270

-15'' 4"-4"'

8

9 10

2.mo

3AOO 4.303

OA4

A

P-tr l'- 0" f' -.6" 3''

B r' -,a·~ l' -:3!' r' -1" 2-' -:On 2·'--s~

SJ ---8''

Qlher Tlian Top Hats 'l'l!nsiiJn Lapt/plice

c

A

:a

J'-2:i>

r;-of'<'

P'-0"

c

P-0'"

l' -7"

Jl-0"'

P-tr'

r

v~-o"

l'-_l~

P-·1"'

i'- 5"

.2' -7" ~· 6"

l' -6"

l' -ll''

4" 7"

2• o•

5' Ill" 7' 5'"

2'-tr 1' 2""

•• TtJp.bar defmedas having•atleast /'- 0" {ll'? ofcancrete below bar.

r~.

s~·

p J l'' 2' 6" . :l' -2»

"'

!"

-.2'~

!'- ltv' 2' .'6''

l-t -.4" 4?

2"

5.'·-~

(f) TellJPtWatUre, Wr!nkqge tmddistriblf(jf)n reilifQrcemenl shall' bt< Ciltss "B". (2) Dowels sha/Jho Class "C" (3) For horizQniXIt bars in• walls, slabs, or bars spaced more than 6" use .,8· (L.4P).

Class ''A"- Low str.ess splice; with ·no mare than="% are.LA.P spltced. C/Ql
_) Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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Anchor recess· Plan

Figure 17.8- Reinforcing Steel at Post-Tensioning Anchors

)

Slings

Delorma lion and da~mage to ref)ar cage during transpqrtation and handling can ~be minimized by using a special lifting frame rmd/or slings or simJJar. Figure 17.9 -Handling ofPrefabricated Rebar Cage

Chapter 17~0 Construction Inspection Guidelines for Concrete Segmental Bridges

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17.5 Recommended Practice for the Initial Inspection and Storage of Post-Tensioning Hardware Initial inspection of the post-tensioning hardware on the project is necessary to verify that the hardware confirms to the approved shop drawings. Initial inspection should consider the issues discussed below. The hardware covered by the shop drawings consists of: Anchors: Ducts: Miscellaneous:

anchor plates, anchor heads or wedge plates, wedges duct, duct tape, duct couplers grout caps, grout inlets, grout vents

(See Figures 17.10 and 17.11)

The shop drawings show dimensions of the individual pieces and how these pieces should be assembled. There usually are at least two different tendon sizes, but sometimes more. All sizes should be covered by drawings and all hardware sizes should be checked. For checking hardware, the contractor must provide a sample of each item selected from the stockpile on the job. Wedges and wedge seats for post-tensioning hardware are subject to machine tolerances which are extremely smalL These tolerances are the responsibility of the post-tensioning materials supplier. The inspector should limit inspection to obvious details such as length and number of pieces used to make up the wedge. Bearing plates are sometimes cut. Tolerances are as follows:

)

Bearing Plate

Anchor Head Wedges and Wedge Seats, Duct Size, galvanized metal

Thickness Length & Width Area

Diameter

±2%% ± 3/16"

- 0.0 s.i. As Bearing Plate Per Manufacturer ± 1/16"

Maoy types of anchors are forgings or castings which may have gone drrough a number of machine operations. The inspector is concerned only with a visual inspection of the surfaces. Casting errors are normally not visible. The conical surfaces for wedges in aochor head should be smooth. The wedge should be able to easily slide into it. The anchor head, if aoy, should bear flush against the bearing plate. The outside surface of wedges should be smooth and cleao and the inside surfaces serrated over their whole length. At the tip of the wedge, the teeth are usually filed down for a short distance to ensure that the strand force is distributed over the length of the wedge. Where the shop drawings indicate that the components should have drilled holes for attachments of any kind, their presence should be checked.

All post-tensioning hardware and duct material should be stored in a manner so that it will be protected from corrosion aod entraoce of foreign materiaL Wedges should be stored inside. Duct material and aochorages should be stored on wooden platforms and protected from the weather. Ends of ducts should be capped to prevent entrance of foreign material during storage .

.J Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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• Permanent Cap -Positive Seal -Integral Vent • Positive Duct Connection

Figure 17.10- Typical Post-Tensioning Anchorages (Strand Systems)

• Bond • Encapsulation • Positive Connections

Figure 17.11-Plastic Duct and Grout Vent Connection


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17.6 Recommended Practice for Inspection of Post-Tensioning Hardware in the Reinforcement Cage Inspection of post-tensioning ducts and other embedded items in the rebar cage is based on approved shop drawings showing location of ducts, rebar, and any other embedded items. In areas where there is congestion of rebar, ducts or other embedded items, two dimensional or three dimensional drawings illustrating location of all embedded items should be included in the contract drawings. The inspector should verify that post-tensioning ducts can be placed in their correct locations in the cage without major relocation or cutting of rebar. The only post-tensioning hardware that can be placed effectively into the rebar cage is the ducts. The advantage of placing the ·ducts into the cage before the cage is placed into the form is that interference problems can be solved at this time without loss of production. Also the number and approximate locations of the ducts can be verified, saving on inspection time at the form. Usually the ducts are placed in their approximate location since they cannot be tied. Before connection with the previous segment and the anchor, which must be made in the form. For resolution of interference problems, see Section 17. 7, "Recommended Practices for Solving Rebar Conflicts. " When the shop drawing calls for grout vents, the vents can be placed in the rebar cage. Anchor reinforcement such as spirals and hair pins should be placed in the cage. However, their final position can only be adjusted after placement of the cage in the form and after the anchor has been installed.

\


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17.7 Recommended Practice for Resolution of Rebar Conflicts Resolution of conflicts between location of embedded items is primarily the responsibility of the Engioeer of Record, and should be resolved duriog the design phase. When the Contractor, makes significant modifications to the post-tensioning details or the length of segments, responsibility for resolution of conflicts between locations of embedded items, and revised details shifts to the Contractor, and the Contractor's Specialty Engioeer. Conflicts io placement of rebar may be resolved by cutting, moviog or bendiog rebar. Cutting of rebar generally requires approval of the Owner's Engioeer (Construction Engioeeriog Inspector). Moviog rebar is generally allowed. Bondiog rebar is generally allowed, but sometimes requires use of hairpios to secure the bond. As shown io Figure 17 .I, bar I will tend to straighten, and a hairpio is needed to maiotaio the shape of the bar. Geometry of bar 2 under tension is maintaioed by the concrete. Recommendations concerning moving or cutting other bars in the cross-section ofFigure 17.12 are presented io Table 17.3.

, ..

T2

1'5

T4

L B3 Figure 17.12 -Aid for Solving Rebar Conflicts

Chapter 17.0 Coostruction Inspection Guidelines for Concrete Segmental Bridges

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~,)

Table 17.3 Recommendations Concerning Moving or Cutting Rebar

Placing Bars

T 1 through T3

Functionffolerance

Very important for strength of slab if deck not transversely prestressed. No cutting ofT 1 through T 3 allowed. If deck is transversely prestressed, T 1 through T 3 can be cut in case of conflicts and lap spliced.

Placing Tolerance

- to face slab ± II.'' - parallel to face of slab± I"

T4, Ts

Structurally not very important whether deck is prestressed or not. Can be cut to avoid conflicts and lap spliced.

- parallel to face of slab± I"

w1,W2

Very important for strength of web. Cannot be cut to avoid conflicts but can be relocated as long as cover (with± II.'' tolerance) is maintained.


W3,W4

Very important for strength of web and, in case deck is not prestressed transversely, also for strength of deck. Cannot be cut or relocated. In case of conflicts, contact the Owner's Engineer. If deck is transversely prestressed, bars can be relocated as long as cover(± W' tolerance) is maintained.

-parallel to face of slab± I"

Very important for strength of bottom slab. Cannot be cut,


) Bt, B2, B3

but can be relocated as long as cover (with± ~" tolerance) is

maintained.

L

Longitudinal bars are structurally not very important. Can be cut to avoid conflicts and lap spliced. Can be relocated.


R 1 ,R2

Structurally not very important. Can be relocated as long as cover (within tolerance) is maintained.

- parallel to face of slab± 1"


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17.8 Recommended Practice for Inspecting Post-Tensioning Hardware in the Form As noted in Section 17.7, the number of ducts and anchors should be checked before the cage is in the form. However, final location can only be achieved and inspected after the cage is in the form. Anchors and ducts are both subject to placement tolerances. As stated in Table 17.1, and as illustrated by the sketch associated with the Table, the tolerance on location of tendon ducts at the face of a segment is± Ys in. This tolerance also applies to the location of anchors. Duct should be rigidly supported at the proper location in the forms by ties to reinforcing steel. Polyethylene duct and metal duct for longitudinal or transverse post-tensioning in the flanges should be supported at intervals not to exceed 2 feet. Polyethylene duct in webs for longitudinal post-tensioning shall be tied to stirrups at intervals not to exceed 2 feet, and metal duct for longitudinal post-tensioning in webs should be tied to stirrups at intervals not to exceed 4 feet. During concrete placement for precast segments, mandrels shonld be used as stiffeners in each duct and shall extend throughout the length of the segment being cast and at least 2 feet into the corresponding duct of the previously cast segment. The mandrels shonld be of sufficient rigidity to maintain the duct geometry within a 1/2 inch tolerance within the top flange, I inch in webs, and within a 1/8 inch tolerance at the segment joints. The recess pocket (see Figure 17.13) determines the angle of the anchor plate and the distance from the face of the segment. The connection between the anchor and the recess must be strong enough to hold the anchor firmly in place dnring concrete placement, and it must also be mortar tight. The recess pocket shonld be constructed within the tolerances shown in Figure 17.1. To minimize fiiction losses when stressing tendons, ducts and anchors should line up perfectly. The tolerance on alignment of duct and anchor is 2 percent as showu in Figure 17.13.

(+) or (-) J/8" Seal

---~~10~0~====]]ot.2 Sltrpe tole.ra'nce :J: 2%

(Outside. Face) minimum= clearance per plans -

J/4 ..

( Jo111l Face) no minimum required. Tolerance on slope of recess pocket

(2){1/8}/12 ~ 1/48 = 1.2%

Reduce oi- increase tolerance with size of recess pocket

Figure 17.13 - Tolerances on Anchor Placement


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17.9 Recommended Practice for Inspection of the Setting of Matchcast Segments Casting curves for setting of matchcast segments are provided on the shop drawings. However, adjustments to these casting curves are usually required during the casting process to compensate for small geometry errors made in the casting of individual segments, These adjustments are based on measurements of elevation and aligmnent of the geometry of individual segments throughout the casting process. Special computer programs developed for geometry control of segmental bridges are normally used to process the casting yard elevation and aligmnent measurements and provide dimensional settings for the geometry of the new segment. These dimensional settings include correction necessary to adjust the geometry of the new segment for any casting errors in the previous segment. The basic requirements and assumptions normally used in geometry control are described in the following sections* * Material presented in this section was developed by Alan Moreton, Corven Engineering, Inc. and reported in "Three Dimensional Geometry Control ofSegmental Bridges with Special Reference to the Linn Cove Viaduct," 1992 (unpublished)/

17.9.1 On-Site Hardware Elevation and alignment control is maintained by casting four elevation bolts and two centerline aligmnent hairpins into the top surfuce of each segment as shown in Figure I 7. 14. Computations are based on the assumption that the bolts and hairpins are at and define the concrete surface at each joint. This means that the bolts must be placed very carefully in the fresh concrete so that they are always very close to the level of the top of the bulkhead at one end and the surface of the match cast segment at the other. The bolts must also be placed exactly at the required offsets from the centerline. These positions should be over the webs in order to be unaffected by deflections of the top slab. Also, the elevation bolts should always be placed at the same, small frxed distance from the bulkhead and match cast segment face. The centerline hai~pins should be placed very close to, or if possible, at the very ends of the segment. There is a danger here that both bolts and hairpins could be lost by spalling - a simple precaution is to use long legs set down at an angle down into the concrete. CNUna ~h:anter.fure (horizontal)

~'I

Centet-rrne hal:fpins

----"\.

.

·)~ .. /

....-;

. _/ '

-· .

C\

Figure 17.14- Geometry Control- Reference Hardware and Axes


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Figure 17.15- Casting Cell Survey Control Arrangement

17.9.2 Measuring Instruments A theodolite mounted on an instrument tower on the centerline of the cell is required at one end of the production line, sightiog onto a reference target mounted on a similar tower at the other Figure 17.15. Accurate offset measurements to the centerline marks can be made with a steel scale fitted

with a leveling bubble (Figure 17.16(a)). It is not essential, but it is convenient to have a surveyor's level mounted on the instrument tower to maintain a constant datum.

Elevations in the castiog cell are related to the joint defined by the top of the bulkhead which should preferably be horizontal and inunovable. (All elevations used to calculate the as-cast positions are actually relative to each other, with the top of the bulkhead joint as the common reference). With most segmental bridges, it is sufficiently accurate to measure the bolt elevations by standing the leveling staff on the domed bolt head. However, with severe super elevation, it is always necessary to measure the elevation at the same required distance from the centerline. At Linn

Cove the center puoch marks for length measurements on the left and right bolts were conveniently used for the elevations by attaching a hardened steel center point to the bottom of the leveling rod (Figure 17.16(b)).

..) Chapter 17.0 Construction Inspection Gnidelines for Concrete Segmental Bridges

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Scale

'/

Spirit leVel

Hard steel point

(a) Offset measuring tool

(b) Elevation rod

Figure 17.16- Measuring Equipment

17.9.3

Observations in the Casting Cell The following observations are required after casting (Figure 17 .17) (a) The elevation on each bolt on the match cast and new cast segments. (Note: that all these bolts must be at a constant distance (w/2) from the centerline for three dimensional geomelly controls).

(b) The offsets from the centerline of the cell to the centerline marks previously made on both ends of the match cast segment (ocl and oc2) and new centerline marks must be made on each hairpin of the newly cast segment. At the bulkhead, this is placed directly on the centerline of the casting cell (offset= 0) and at the match cast face, at the same offset as on the adjacent match cast hairpin (ocl). (c) The exact length measurement of the newly cast segment at the centerlines of the left and right elevation control bolts. These are essential to the 3D method. They are made by making a center punch mark on each of the A and C elevation bolts and taking the lengths between like bolts on the cast and match cast segments. (i.e. between A and AI and between C and Cl). (d) The small distances of the bolts and centerline hairpins from the joints (db and de respectively). It is to be noted that on some projects, the joints were truly radial and not perpendicular to the chords of the segments. This has implications for the casting machine and the derivation of the joint geometiy. See Section 17.10. A sample data sheet for the recording and processing of observations using the three dimensional geomelly control system, is shown in Figure 17.18.


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y

t

±

)

'

........

..12

Jolnlll

'1112

Bl

'

.I

'

' ·~1

~

:!

.... .... Joint I

I

'

~

Loft

11,. JoJnt,B Bulkhead

X

Origin of tocaJ cell' coordinates

Figure 17.17- Observations (After Casting)


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Figure 17.18- Three-Dimensional Geometry Control Data Sheet

Project: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Date: _ _ _ _ _ _ __ Observing Engineer: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ THREE DIMENSIONAL GEOMETRY CONTROL PROGRAM INPUT

Match Cast Segment N o . - - - - - - - -

Newly Cast Segment No . _ _ _ _ _ _ __

Joint II Reference No. _ _ _ _ _ _ _ _ __

Joint 1 Reference No. _ _ _ _ _ __

Bulkhead Joint Reference No. _ _ _ _ _ __

Rod Reading Ad Previous Input Value

BI~

m~

Alpha~

Gamma=

_____

Ron READINGS (INPUT)

[AI- B] and [Cl- D] from previous casting Alpha~

Gamma~

en~-----

AJI~

de_ _ _.

db·-~---

NOTE MINOR HARDWARE DISTANCE FOR CORRECTIONS (if needed):

LENGTH (INPUT

A B

LRM LLM LRC LLC

c D

AI All

From previous casting From previous casting - - - - - - ' - - - - - - From new casting observations - - - - - - ' - - - - - - From new casting observations

w

CI

Width between elev. bolts Centerline offset joint I Centerline offset ·oint II

ocl oc2

CII

CHECK TWIST (OBSERVATIONS):

(INPUT) DIAGONAL DIMENSIONS OF MATCH CAST SEGMENT:

DMI DM2 DM3 DM4

( DI-CJ) +(AI- 81) LRM I LLM ~ ._ _ __ Compare with data from previous casting:

[ DI-CJ] +[AI- 81] LRC I LLC

~

._ _ __

Check Twist {processing) okay- yes I no?

From previous casting

OUTPUT: Record new Alpha and Gamma for processing next casting: Alpha~

[AI- B]

Gamma~

~

[AI- 8] ~

RECORD DIAGONAL DIMENSIONS OF NEW CAST SEGMENT:

DC3 DC4

DC! DC2

RECORD GLOBAL COORDlNATES OF NEW JOINT (BULKHEAD JOINT)

Left

Cent{!r

Right

Eastings (X) Northings (Y) Elevation Z

'.) Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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17.10 Recommended Practice for Concreting Segments Concreting segments in oqe continuous operation prevents cold joints. Casting joints are generally not allowed. The recommended sequence for placing segment concrete is showu in Figure 17.19. This sequence is valid only for regular segments. A different procedure must often be followed for pier and abutment segments. The difficulty in pouring segments is due to the fact that the bottom slab does not have a top form. Therefore, concrete that is placed in the web will flow into the bottom slab if vibrated strongly. The pouring sequence showu allows proper consolidation of concrete in the bottom of the web and finishing the surface of the bottom slab. The most important issue for finishing the bottom slab is make sure that the slab thickness meets the tolerances. Concrete is placed first in the bottom slab. Placing this concrete is a little more time consuming since it needs to be done through a chute or gutter. Then, concrete will be placed through the web in the bottom corners. Upon vibrating the web concrete tends to flow into the bottom slab. Care must be taken to minimize the flow and yet obtain good consolidation. After completion of these pours, the webs can be filled. Workers go from one web to the other in order to ensure that the concrete in both webs rises equally. High webs must be poured through a chute. The deck slab is poured last. One sequence for placement of concrete in a segment is shown in Figure 17.19. Other placement sequences have also been used successfully. The concrete should be vibrated in accordance with normal vibrating practice. Care should be taken in vibrating pour I since the concrete will keep flowing out of the webs as long as vibrating continues. Post-tensioning anchors should receive special care during vibrating. The close windings of the spiral sometimes prevent the concrete from filling the space behind the anchor and inside the spiral. Ducts for post-tensioning tendons can be moved or damaged by concrete. This may occur during placing of concrete or during vibrating. Iftendons are located at the intersection of web and bottom slab, the pressore caused by vibrating can easily move the ducts if not properly secured. If a duct becomes dislodged at a location which is difficult to access, the segment may be lost. Time available for repair is 30 minutes at the most. After that, cold joints will occur which must be repaired acceptably. Minor damage to ducts can sometimes be restored by chipping away the hardened concrete around the ducts. This concrete must also be repaired.


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In many cases, the top slab is the riding surface. The finishing operation is therefore important and should be carefully inspected. The top of the slab should be first struck off either by hand or mechanically. Either a vibrating or rolling screed works well for an initial pass and leveling. The surface should then be worked using a straight edge from the bulkhead to the matchcast segment and a light application ofbullfloats to provide a smooth, even, uniform dense fmish. Cylinders are broken for each major event. Check strength for stripping forms Check strength for segment transport Check strength for transverse post-tensioning Check strength for completion of curing Check strength for 28-day strength Check strength for spare Total

I cylinder I cylinder I cylinder I cylinder 3 cylinders I cylinder 8 cylinders

The cylinder for checking strength for stripping should be stored with the segment under the burlap placed on the deck. This duplicates early strength results closely. Remove the cylinder just prior to breaking. Match-cured cylinder mold or maturity measuring devices may also be used for measuring early strength.

II

12

Figure 17.19- Casting Sequence for Regular Precast Segments


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17.11 Recommended Practice for Inspection of Curing of Segments By specification, the Contractor has the option to use the curing method set out in the Special Provisions or to propose an alternate curing method. The following method is based on steam curing typically used in Florida. The curing process involves the following steps; each of which requires verification by the inspectors. •

After casting, segment is to be kept in ambient air of 50 F. or above. If air temperatore is too low, raise by introducing steam or heat using direct heaters .

• •

After casting, segment is to be covered with burlap and kept wet during pre-steaming period or covered with curing blankets held just clear of the top surface and having no gaps.

•

Upon completion of the four-six hour pre-steaming period, the segment is to be steam cured. Specifications provide the details of the steam curing cycle.

•

Upon completion of the steam curing cycle, check strength, strip forms and move segment to "old" match cast position.

•

While the segment is in the "old" (matchcast) position, continue curing by the application of an approved curing membrane to all exposed surfuces except the end joint faces. These should be coated with an approved bond breaking compound which will also act as a "seal" for curing. Curing may continue in this manner until the segment is at least 72 hours old and the strength is at least 4000 psi.

•

When it is in the matchcast "old" position, the segment receives a second curing in conjunction with casting of the next segment.

•

After completion of the second steam curing cycle, check strength of old segment. If the cylinder break is 4000 psi or higher, stop curing. If break is less than 4000 psi, continue curing in storage until segment is 72 hours old. Curing in storage is by placing wet burlap on top and hanging over all sides. Burlap is covered with Polyethelene sheets.


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\

)

17.12Recommended Practice for Inspection of Stripping Forms and Bond Breaking The following steps are recommended relative to the stripping of forms aod breaking the bond between segments: 1.

Check strength of segment prior to giving permission to strip forms. The strength required for stripping forms has been provided on the plaos or in the special provisions. Also, shop drawings should be checked for ao indication whether or not traosverse post-tensioning must be stressed before forms can be stripped off.

2.

Upon removal of inner form and outer form, check webs for casting defects. If casting defects are present (honeycombing near aochors for example), this is the most suitable time to determine whether or not the segment will be accepted. If not accepted, it can be removed and a new one made. If it is likely that the segment cao be repaired, it should be accepted provisionally subject to acceptable repair.

3.

After removal of forms, break bond between "old" and "new" segments. Breaking bond is accomplished by the method or process shown on the shop drawings. This process must ensure separation of the segment without damage to the keys or the face of the segment.

4.

Inspect joint between the "old" and "new" segment for key breakage. The keys ensure that the weight of the last segment of a caotilever will be carried by the caotilever. Generally, the margin of safety allows a small percentage of the keys to be broken. Guidelines for the extent of the damage permissible to keys should be submitted by the contractor and approved for use. It is not recommended that keys are repaired prior to erection. Any repair made to the matchcast surfaces will lead to fitting problems aod usually to severe spalling upon erection. The better practice is therefore to establish a guideline for acceptable key breakage aod make the repair after erection.

5.

Ensure that the correct number is painted on the segment. The numbering system of segments is part of the contractor's shop drawing submittal. The number indicates where the segment will be stored and erected. It is very irnportaot that the segment be numbered correctly with the direction of stationing.

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17.13Recommended Practice for Inspection of Segment Handling in the Casting Yard 1.

Segment handling in the casting yard should be in accordance with an approved segment handling procedure. Segment handling in the yard consists of lifting the "old" segment off the bottom form, traveling with the suspended segment to storage and placing it on a prepared foundation. The procednre tn be submitted and approved describes: (a) The crane, movement, boom, safe working loads. (b) The lifting frame. This is a device which distributes the lifting force to generally fonr pickup points (see Fignre 17 .20). (c) The attachment of the lifting frame to the segment

2.

The inspector must verify that the required concrete strength for handling is achieved. The concrete strength required for lifting the segments is provided in the special provisions. If not, it should be proposed by the contractor and approved for use.

3.

The inspector must verify that that the lifting frame is safely attached to the segment. These attachments are generally bolts (Fignre 17 .20) which go through the top slab. These bolts shouid be evenly torqued. For lighter segments lifting loops are sometimes used. These loops should bear evenly against the pipe or dowel passing through the loops. Lifting loops should be placed with a template prior to casting to ensnre this. C hooks shonld be carefully positioned with the lifting line in the center of gravity of the segment. If used, the contractor submits this location for each different segment type and the inspector should verify that it is placed properly.

Turnbuckles or jacks for control of crossfall

C-flook

Adjusting lateral posWon of frame will allow segment to

hang at required cross/all with a single central Jill.

hardwood packs to a void damage to corners when lifting

7

with slings.

Post- tensioning. bars

Shim Profiled shim

Figure 17.20- Handling Segments


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)

17.14 Recommended Practice for Inspection of Repairs Made to Segments The inspector should verify that there is au approved repair procedure aud that this procedure is being followed. The repair procedure should address the following: A. Repair of Voids (honeycombing) involves considerations related to the appearance of the repair, the durability of the repair, and the structural adequacy of the repair as discussed below.

The appearance ofthe repair concerns color and surface finishing. Since most repairs are darker than the surrounding concrete, it is best to make trial mixes of the mortars proposed for repairs at the time of approval so that color differences can be judged. These trial mixes should be made before they are needed. Much skill is required for making good looking repairs. Part of the procedure submitted by the contractor should be names and qualifications of the person(s) making the repairs. Durability of repairs is determined by the quality of the repair material and the bond of the repair material to the old concrete. Bond is determined by surface preparation, type of binding agent and method of filling the void. The different types of voids require treatment. Figure 17.21 shows repair of a hole in the web which can be effectively repaired, more easily than surface damage. Other issues to be addressed are curing and shrinkage of the repair. Structural adequacy is determined by the location of the void in the structure. Segmental box girders are often over-designed. The high concrete strength of5500-6000 psi is usually only needed in the support area (bottom slab and webs) and in post-tensioning anchor zones. In other areas, it ensures a high quality and durable product. Therefore, repairs may often be judged by their durability rather than by structural adequacy. Structural adequacy is generally assured by the composition of the repair mix. This mix should have adequate strength, and it should be a concrete mix. This means that it should depend on cement aud not on an epoxy resin or similar material for strength. Such materials are strong but also more elastic than concrete and cannot therefore always perform a structural function. B. Repair of Cracks. Most cracks over a certain size are repaired by epoxy injection. This is

specialty work and the repair procedure should address: (I) Qualifications of the applicator. There is a variety of specialized firms who all have their own products. The proposal for the injection procedure should include the range of products offered and their chemical and physical properties so that an engineering judgment can be made about their suitability. (2) Crack size to be injected. In aggressive environments, some agencies require epoxy injection of cracks over 0.008". These cracks can be measured with optical crack meters. For more guidance on repairs

of cracks, the inspector should refer to supplementary specifications .

.. J Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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(3) Responsibility for cracking. Cracks are not always a consequence of the contractor's methods. If a contractor fabricates a segment in accordance with the plans and Special Provisions and cracks develop, the contractor is not responsible and should not bear the expense of epoxy injection. If cracks are a consequence of handling, design revisions, errors made in pouring, curing, mix, supports, stacking, the contractor should bear the expense of the injection.

C. An inspector should be present while a repair is being made. Any defect discovered in a segment will be cause for delays, costs, meetings, etc. All are reasons for a well-meaning superintendent to cover up the defect before it is discovered. This is uoacceptable practice. Repairs thus made should be removed and redone in the presence of an inspector. The inspector should also be present when forms are removed from a segment so that he has frrst hand information about defects when these occur. D. The inspector shonld ensure that no repairs extend into the joint faces. Repairs of joint faces and shear keys should not be made. If defects occur in the joint faces, the repair should be postponed until after the erection of the segment. Any doubt about feasibility of repair of voids or cracks should be resolved by consultation between the Construction Engineering Inspector and the Construction Engineer.

3:1 Slope

Wrong

1-Piece form

Form designed for 1:2" !ills Figure 17.21 -Repair ofHoneycombed Area


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17.15 Recommended Practice for Inspection of Segment Storage The inspector should verify that there is ao approved procedure for storage of segments. The procedure indicates how, where aod on what material the segments are supported aod whether or not double stacking is allowed. It also indicates the layout of the storage area aod the order of placing and removing segments. In addition, the contractor usually performs work in the storage

area, such as curing, transverse post-tensioning, finishing recesses, repairs of cracks, honeycombing, aod surface finishing. Some of these tasks, such as transverse post-tensioning and repairs, require the presence of an inspector. The inspector should ensure that suitable material is used to support the segments which will cushion the load eveuly. Oak blocks are often used. Supports are placed under the webs because the load bearing capacity there is much higher thao at aoy other location. The bottom slab could not handle the load without cracking. Three (3) supports are provided per segment- two under one web near the ends aod a third in the middle of the opposite web (see Figure 17 .22). This method provides predictable bearing forces aod will support the segment eveuly. In case of double stacking, the support blocks should be placed correctly on the lower segment (see Figure 17.22). If webs are not vertical, the second segment is supported on the top slab of the lower segment. This will bend the slab. The contractor will take this bending effect into account when he proposes double stacking, but it is important to realize that this proposal is based on placing the supports correctly. The shop drawing should provide size of supports and exact

location and tolerances. A tolerance of± 1" on size of support blocks and± 2" on their location should be workable.

0

\

I

\'-=!=;._,...; I '-

deflection

Suppart Pli!~ed

Corz7Jct

Figure 17.22- Stacking Segments

') Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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17.16 Recommended Practice for Inspection of Segments for Payment In reviewing segments for payment, the following details or criteria should be reviewed by the inspector and fouod to be acceptable:

•

Segments should have a uniform appearance. This means even color and few or minor surface defects. The most common surface defect is that caused by air bubbles. This occurs when plywood or steel forms are used but seems to be somewhat controllable. If size (more than 1/2" diameter) and number are such that the quality of the segment is clearly affected, the bubbles have to be sealed in accordance with an approved repair procedure.

•

Generally the bond breaker will adhere to the joint faces and will have to be removed by very light sandblasting. The sandblasting also should remove the laitance. Thus, the epoxy will be applied to strong material and will provide an excellent bonded joint with high tensile strength. The sandblasting should be as light as possible to achieve this. Strong sandblasting can remove too much material which would reduce the fit obtained with the matchcasting procedure.

•

Ducts should be checked for alignment and cleanliness and anchors and recesses for presence of mortar. Recesses should be cleaned out so far that the jack will fit into it. Anchors should be entirely free from mortar.

•

Segment dimensions should be within the tolerances in Table 17.1

•

The segment should be checked for cracks, spalls, damage to keys and repairs including repairs on matchcast faces.

•

Any defect should be repaired in accordance with the approved repair procedure, and the repair should be approved before payment for the segment is made.

•

The 28-day strength of the segment should be checked. If the 28-day strength is not achieved, it should be decided whether or not to accept the segment.

:) Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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17.17Recommended Practice for Inspection of Segment Transportation Segments handling normally consists of removing segments from storage, placing the segment on a vehicle, moving the segment to the job site, unloading and storing the segment on-site, unloading and storing the segment on-site, and lifting the segment for erection. Ideally, that the contractor will use the same method of suspending the segment for all handling operations. However, this is not always the case. While in the yard a sling may be used; on site the contractor may use a lifting frame or C-hook. The different handling methods should be covered by calculations ofthe suspended segment. These calculations should differentiate between the stage where transverse post-tensioning is stressed or unstressed. Segments are usually handled and stored strictly according to the approved procedure in the casting yard. The same arrangements, however, are required on site. The support conditions on vehicles are the same as in the yard. Calculations ofloading during transport by vehicle should include an impact factor of 1.5. For transport on a barge, this is not required. The inspector should verify that the contractor has obtained all the required permits for roadway transportation and that the contractor has the means to honor the requirements of these permits. Since this concerns heavy transports, permits are usually required for overloads and illegal widths. These need to be obtained by the contractor. If the transport involves maintenance of traffic problems, the inspector should ensure that there is an approved maintenance of traffic plan. It is also necessary for the inspector to ensure that the contractor has informed all the parties involved and enforce the maintenance of traffic plan. Maintenance of traffic problems often occur in case of heavy transports, cranes and segments. Usually these have been anticipated by the designer and are covered by special provisions.


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17.18 Recommended Practice for Inspection of Erection Equipment The inspector should determine that there is an approved erection manual, and should read and understand the manual. In event of any questions, the inspector should discuss the manual with the contractor or a designated representative of the contractor.

The erection manual will indicate the type of equipment the contractor proposes to use. Usually this will be cranes. The manual will describe lifting capacity of the crane at the maximum boom required and where the crane will be placed.

In case of crane erection, erection manuals will be simple documents indicating erection sequences, descriptions of basic operations, geometry control data and stressing data. In case of erection methods using special equipment such as erection trusses, launching girders or gantry, the erection manual will be more complicated. Inspectors should, however, not be asked to work with erection manuals too complicated to implement, inspect or even understand. For an example, an

erection manual describing movement of a launching girder in 30 steps, each of which can lead to problems if not executed correctly, should not be approved for use. In any case, the steps should be clear. The rated lifting capacity of the crane assumes that the crane has a firm place to stand, outriggers can be placed properly and boom will not be exceeded. The inspector should ensure that any custom designed equipment used for the project has been inspected by inspectors qualified to perform such inspections. The inspection of special equipment should be performed by qualified persons. The inspector should be familiar with cranes, welds, or bolted connections as dictated by the erection equipment.

The inspector should verifY that there is an operation manual for custom designed equipment. Since neither the designer nor the fabricator of the equipment will operate it, a comprehensive manual is required for this. The manual should be understandable to the operator. The manual should preferably not only address how to operate the equipment correctly, but also what can go wrong. Especially in case of heavy equipment, it is very important that operations are simple. The inspector should verifY that a test load program of the equipment has been planned and that this program is implemented. This test loading program should be designed in such a way that all operations are tested, not only lifting but also moving the equipment in both loaded and unloaded conditions. The inspector should ensure that the circumstances assumed for operation of erection equipment are in fact, existing in the field. In some known cases, equipment failed during test loading or first use. Often the reason was that design assumptions were not in agreement with field conditions. The inspector should ensure that that the equipment operator is experienced in accordance with project requirements, and is instructed to transfer loads from equipment to structure gradually.

Sudden release of the segment from the crane will magnify the effect of the segment weight and will apply forces to the structure it has not been designed to support.


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17.19

Recommended Practice for Inspection of Falsework 1.

Ensure that falsework is built from approved plans. Falsework used for construction of segmental bridges is subjected to heavy loading. Consequences of a failure can be disastrous and the design for such falsework should therefore be prepared with the same care as the bridge plans themselves. There should be a good set of drawings supported by calculations. Construction of the falsework should be inspected. A good guide for the design and inspection of falsework is the "California Falsework Manual" available from Caltrans.

2.

Ensure that the plans indicate assumptions for subsoil conditions and seek evidence that these assumptions are met or exceeded in the field. Usually falsework is supported on spread footings so subsoil conditions come into play. Geotechnical advice is required to both ascertain safe bearing capacity as well as predicted settlements. Predicted settlements are needed in order to be able to set the elevation of the top of the falsework. A tolerance for settlements must be provided in the plans. If exceeded, the falsework designer must be notified.

3.

Check that the falsework is erected in accordance with the approved plans. Also have the designer of the falsework inspect it. In case of specialty systems, ensure that the manufacturer's erection instructions are being followed. Because of the temporary nature of the work, falsework plans are sometimes not treated with the same care as bridge plans. In addition, the contractor often substitutes joist sizes and modifies the plans as he sees fit. This practice has been the cause of serious failures. Inspection of the falsework by the designer should make the contractor aware of his responsibilities. Erection of specialty systems requires strict adherence to manufacturer's instructions. Inspection of the erection by a manufacturer's representative should provide the necessary assurances.

4.

Monitor the falsework while it is being loaded and at regular intervals after it has been loaded. When the falsework is being loaded, check for excessive member deflections and shifting of members. Monitor jacks. Use an instrument to check settlement of footings. In case the falsework is to be in service for a long time, monitor the condition of the falsework and the settlement periodically.

5.

Check that elevations of the top of the falsework are as required and ensure that anticipated settlements are taken into account. Footing settlements cause the final elevations to be lower. It is a good practice to estimate beforehand the amount of settlement expected and compensate for this in setting the elevation of the top ofthe falsework. Such estimates are made by geotechnical engineers and should be provided on the plans.

6.

Ensure that no components of the falsework can be hit accidentally by construction equipment, traffic, etc. Often openings in falsework are provided to allow passage of traffic, equipment, etc. Safety barriers need to be placed so that falsework cannot be hit.


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17.20 Recommended Practice for the Inspection of Epoxy Joints I.

Ensure that the epoxy resin is approved for use on the project. The Special Provisions require completion of several tests to be made on the epoxy resio. The approved epoxy will have passed these tests.

2.

Ensure that the contractor is implementing the safety recommendations from the supplier. Containers with epoxy resin carry warnings regarding toxicity of the materials and iostructions in cases of emergency. The contractor should point out the hazards to the workers and should have the required supplies available on site in case of an emergency.

3.

Ensure that a supplier's representative is present at the time of first use on the project. The consequences of errors made in mixing, application and removal of epoxys are costly and generally unnecessary. The presence of a manufacturer's representative thoroughly familiar with the product pays off, and the inspector should insist on it. For maximum benefit, all persons working with the material should be present at this first application.

4.

If there are several types of epoxy on the project, ensure that labeling is such that they cannot be interchanged. Epoxy resins must be formulated specially for a variety of conditions. The ambient temperature is most important. An epoxy resin formulated for use in cold weather would set ahnost immediately if used in warm weather. Reversely, an epoxy resin formulated for hot weather would cure only after a long time if used in cold weather. Since weather conditions vary, epoxy resin suppliers formulate their product for a particular weather condition and if erection over several seasons is anticipated, there will be several formulations supplied. These should be kept apart.

5.

Ensure that the two components of the epoxy are properly mixed. Epoxy consists of a resin and a hardener, often referred to as components A and B. As long as these are kept separated, the resin will not set. In order to function as designed, the two components A and B must be very thoroughly mixed. If not, the resin will not set. Improper mixing has been the cause of high repair costs. Good mixing is generally ensured by: (a) Using manufacturer1s recommended equipment in accordance with manufacturer1s instructions. (b) In addition to the above, using different colors for components A and B. If the color of the mix is uniform, the resin and hardener are properly mixed.

6.

Ensure that pot life and open time requirements are adhered to. Although there is a certain safety range, one should understand that epoxy will bind and cure only if used within these specified time limits.

7.

Ensure that joint faces are properly prepared. A good bond of the epoxy to the concrete is only achieved if the joints are dry and clean. (a) Dry is usually defined as "absence of surface water". This means that epoxy cannot be used when it rains. Also, after a rain, the joints should be dried off (preferably with a moderately hot torch). (b) Clean means that the joint has been lightly sandblasted to remove cement paste and bond breaker and that subsequent soiling is removed by wire brush.


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...

8.

Ensure that conditions for use of epoxy are met. The conditions for use of epoxy are humidity (see item 7) and ambient temperature range as prescribed by the manufacturer and/or specifications.

9.

Ensure that the epoxy is properly applied to the joint faces. Usually the Special Provisions indicate the amount of epoxy per square foot of joint or the average thickness of the layer, also whether or not the epoxy has to be applied on one or on two faces. Epoxy needs to he placed in between tendon ducts so that a seal is formed at each duct which should prevent grout from crossing over into ducts other than the one being grouted. Usually workers apply epoxy with a gloved hand. Though primitive, this is a most effective method.

10. Ensure that excess epoxy is removed from exterior joint faces. Since epoxy is applied to the joint in a much greater quantity than required for filling the joint, much of it will be squeezed out upon applying the temporary prestress. This excess forms a bead at the joint faces, on both the inside and outside of the box girder. On the inside, this bead is usually left in place. On the outside, however, this is unsightly and treatment is necessary. Treatment first of all means that the outside should be accessible for work and inspection. The treatment can consist of removing the epoxy with a tool as long as it is soft. This will leave a mark accentuating the joint. In case the box will receive a surface treatment, this is the simplest way to remove the epoxy bead. Alternatively, the epoxy can be removed without leaving marks by chiseling it off after it hardens. This, however, is more time consuming.

11. Ensure that excess epoxy is cleaned from tendon ducts. As epoxy beads form on the outside, the same occurs at the tendon ducts. Squeezed out epoxy will enter the ducts. This epoxy is removed by inserting a brush with a long handle into each duct. This is done immediately after applying the temporary post-tensioning and releasing the segment from the crane. 12. Ensure that the curing process is being monitored. Epoxy will perform its function, which is to provide tensile strength at the joint and seal the joint from moisture penetration, only if it is cured. Normally the epoxy will cure, but on occasion, a bad batch or badly mixed batch will not set. In order to monitor this, simple field tests have been devised such as gluing a small concrete test cube against the inside of the box with the epoxy used for the joint. The next day a firm blow with a sledge hanuner will either fail the epoxy or the concrete. Although not very scientific, this "test" surely indicates whether or not something is obviously wrong. The special provisions may prescribe tests to be performed on the epoxy during erection. Such tests usually apply to the strength ofthe epoxy. If, for some reason, a segment cannot be erected and epoxy has been applied to the joint faces, the epoxy must be removed. In order to avoid delays, the contractor should submit a procedure for this for approval. The usual procedure consists of:

(a) Scraping off as much of the epoxy as possible while it is still soft. (b) Bum off the remainder with a low heat torch. (c) Sandblast the joint to thoroughly clean the joint.

13. Ensure that tests prescribed by the Special Provisions to be performed during erection are made. 14. Ensure that there is an approved procedure for removal of epoxy from joint faces.

"J Chapter 17.0 Construction Inspection Guidelines for Concrete Segmental Bridges

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17.21 Recommended Practice for Tendon Stressing All aspects of tendon stressing should be in accordance with Chapter 3, "Post-Tensioning Duct and Tendon Installation" of the FHWA "Post-Tensioning Tendon Installation and Grouting Manual. " Special care should be given to observation of the safety guidelines for stressing of post-tensioning tendons presented in Chapter 11.

17.22 Recommended Practice for Inspection of Grouting Inspection of grouting should confirm conformance with the recommendations of Chapter 4, "Grouting ofPost-Tensioning Tendons" of the FHWA "Post-Tensioning Tendon Installation and Grouting Manual. "

17.23 Recommended Practice for Inspection of Cast-in-Place Segmental Structures The recommended practice for inspection of precast segmental structures is, with few exceptions,

also valid for cast-in-place segmental work. Exceptions are those operations strictly related to the techniques such as geometry control, segment handling, etc. which obviously do not apply. Form tolerances for cast-in-place segmental bridges should be adhered to with great care. A form which produces heavier segments on one of the cantilever arms will have a large effect on the unbalanced moment. The geometry control for cast-in-place segmental bridges is less demanding since it is almost "self-correcting." Curing on the other hand is more critical since the progress of

the work depends on the concrete achieving early strength. Post-tensioning generally occurs long before the concrete achieves design strength and post-tensioning anchor sizes may have to be adapted for use with lower strength concrete. The sequence of segment concreting has to be

adapted to the flexibility of the form carrier.


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ASBI-Construction-Practices-Handbook-for-Concrete-Segmental-and-Cable-Supported-Brdiges.pdf

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