Acelerated Precast Bridges PCI

GUIDELINES FOR ACCELERATED BRIDGE CONSTRUCTION

USING PRECAST/PRESTRESSED CONCRETE COMPONENTS PCI NORTHEAST BRIDGE TECHNICAL COMMITTEE

GUIDELINES FOR ACCELERATED BRIDGE CONSTRUCTION USING PRECAST/PRESTRESSED CONCRETE COMPONENTS

PCINER-06-ABC

First Edition Cover Photo: Davis Narrows Bridge courtesy of the Maine Department of Transportation

116 Radcliffe Road | Belmont, MA 02478 Phone (888) 700-5670 | http://www.pcine.org

PCINER-06-ABC Copyright © 2006 By Precast/Prestressed Concrete Institute Northeast First Edition, first printing, 2006 All rights reserved. This guide or any part thereof may not be reproduced in any form without the written permission of the Precast/Prestressed Concrete Institute Northeast. Information contain in this work has been obtained from sources believed to be reliable. PCI or its memberships shall not be responsible for any errors, omissions or damages arising out of this information. PCI has published this work with the understanding that PCI is supplying information only. PCI is not rendering engineering or other professional services through this guideline. If such services are required, please seek an appropriate professional.

Printed in the U.S.A

FORWARD This manual has been developed for the purposes of promoting a greater degree of uniformity among owners, engineers and industry of the Northeast, with respect to planning, designing, fabricating and constructing highway bridges with the FHWA’s philosophy of accelerated bridge construction. In response to needs determined by Northeast Transportation Agencies, and Prestressed Concrete Producers, the PCI Northeast Regional Bridge Technical Committee established a subcommittee comprised of a cross section of its members representing academia, transportation engineers and producers to prepare this guide. Contributors were: Accelerated Bridge Construction Sub Committee: Rita Seraderian, PCI Northeast Executive Director (PCINE) Michael P. Culmo, Vice President of Transportation and Structures, CME Associates, Inc. Peter Stamnas, Project Manager, New Hampshire Department of Transportation (NHDOT) Charles Goodspeed, University of New Hampshire, FHWA Eric Calderwood, Principal, Calderwood Engineering etc. George W. Colgrove III, Project Engineer, Vermont Agency of Transportation (VTrans) The PCI-NE Bridge Tech Committee: Eric Thorkildsen, Collins Engineering Vartan Sahakian, Commonwealth Eng. & Consult. Joe Carrara, J. P. Carrara & Sons Ernie Brod, J. P. Carrara & Sons Ed Barwicki, Lin Associates Michael Kane, Mabey Bridge Nate Benoit, Maine DOT Robert Bulger, Maine DOT Maura Sullivan, Mass. Highway Department Alex Bardow, Mass. Highway Department Edmund Newton, Mass. Highway Department David Scott, New Hampshire DOT Duane Carpenter, NYSDOT Matthew Royce, NYSDOT Mike Savella, State of Rhode Island DOT

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PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE vi

TABLE OF CONTENTS FORWARD............................................................................................................................................................ V TABLE OF CONTENTS .....................................................................................................................................VII INTRODUCTION................................................................................................................................................. XI SECTION 1: APPLICATION OVERVIEW .......................................................................................................1-1 1.1 When to Use Accelerated Construction..............................................................................................1-1 1.2 Rehabilitation PROJECTS..................................................................................................................1-2 1.3 Examples of Prefabricated Components.............................................................................................1-2 1.4 Architectural Treatments ....................................................................................................................1-5 1.5 Definitions ..........................................................................................................................................1-5 SECTION 2: GENERAL REQUIREMENTS .....................................................................................................2-1 2.1 PARTIAL REPLACEMENT PROJECTS .........................................................................................2-1 2.2 Design .................................................................................................................................................2-1 2.3 Geometric Configurations...................................................................................................................2-1 2.3.1 Bridge Layout.................................................................................................................................2-1 2.3.2 Component Sizes and Shapes.........................................................................................................2-2 2.4 Tolerances...........................................................................................................................................2-2 2.5 Shipping and Handling .......................................................................................................................2-2 2.5.1 Lifting Devices ...............................................................................................................................2-3 SECTION 3: PRECAST COMPONENTS ..........................................................................................................3-1 3.1 Piling...................................................................................................................................................3-1 3.2 Substructure Components ...................................................................................................................3-1 3.2.1 Footings ..........................................................................................................................................3-1 3.2.1.1 Construction on Bedrock ...........................................................................................................3-1 3.2.1.2 Construction on Soil...................................................................................................................3-2 3.2.1.3 Construction on Piles .................................................................................................................3-3 3.2.1.4 Leveling Devices........................................................................................................................3-3 3.2.1.5 Grouting Under Footings ...........................................................................................................3-4 3.2.2 Wall Segments................................................................................................................................3-4 3.2.3 Columns..........................................................................................................................................3-6 3.2.3.1 Round vs. Rectangular ...............................................................................................................3-6 3.2.4 Girder Support Components...........................................................................................................3-6 3.2.4.1 Pier Caps ....................................................................................................................................3-7 3.2.4.2 Integral Abutment Pile Caps ......................................................................................................3-7 3.2.4.3 Seat Adjustment Beams .............................................................................................................3-8 3.3 Superstructure Components................................................................................................................3-9 3.3.1 Girders and Beams .........................................................................................................................3-9 3.3.2 Full Depth Deck Slabs....................................................................................................................3-9 3.3.3 Stay-in-Place Forms .....................................................................................................................3-10 3.4 PROPRIETARY Bridge Systems .....................................................................................................3-11 3.5 Bridge Railing...................................................................................................................................3-11 SECTION 4: JOINTS ..........................................................................................................................................4-1 4.1 General................................................................................................................................................4-1 4.2 Layout of Joints ..................................................................................................................................4-1 4.3 Structural Joints ..................................................................................................................................4-2 4.3.1 Moment Connections .....................................................................................................................4-2 PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE vii

4.3.2 Shear Connections..........................................................................................................................4-3 4.3.3 Pile Connections.............................................................................................................................4-5 4.3.4 Anchoring Devices .........................................................................................................................4-7 4.4 Non-Structural Joints ..........................................................................................................................4-8 SECTION 5: GROUTING ...................................................................................................................................5-1 5.1 Sub-Footings.......................................................................................................................................5-1 5.2 Component to Component grouting ...................................................................................................5-1 5.2.1 Horizontal Surfaces ........................................................................................................................5-1 5.2.1.1 Area Below Precast Footings .....................................................................................................5-1 5.2.1.2 Recessed Key Connection..........................................................................................................5-1 5.2.1.3 Recommended Grouting Procedure ...........................................................................................5-2 5.2.1.4 Non Recessed Connection .........................................................................................................5-3 5.2.2 Vertical Surfaces ............................................................................................................................5-3 5.2.3 Mechanical Grouted Splices...........................................................................................................5-3 5.3 Pile Caps .............................................................................................................................................5-4 5.4 Post Tensioning Ducts ........................................................................................................................5-4 5.5 Blockouts for Anchoring Devices.......................................................................................................5-5 SECTION 6: SEISMIC CONSIDERATIONS ....................................................................................................6-1 6.1 General Criteria ..................................................................................................................................6-1 6.2 Connection of Superstructure to Substructure ....................................................................................6-1 6.2.1 Keeper Blocks ................................................................................................................................6-1 6.2.2 Pilasters ..........................................................................................................................................6-2 6.2.3 Abutment Backwall ........................................................................................................................6-2 6.2.4 Anchor Rods...................................................................................................................................6-2 6.2.5 Integral Connections.......................................................................................................................6-3 6.3 Column Connections ..........................................................................................................................6-3 6.3.1 Column Base and Cap Connections ...............................................................................................6-3 6.3.2 Splices Along Column Length .......................................................................................................6-4 6.3.3 Confinement Reinforcement ..........................................................................................................6-5 6.4 Footings ..............................................................................................................................................6-5 6.4.1 Internal reinforcement ....................................................................................................................6-5 6.4.2 Pile Uplift .......................................................................................................................................6-5 SECTION 7: FABRICATION/CONSTRUCTION .............................................................................................7-1 7.1 Contractor Options..............................................................................................................................7-1 7.2 Lifting Devices ...................................................................................................................................7-1 7.2.1 Corrosion Protection.......................................................................................................................7-1 7.3 Equipment...........................................................................................................................................7-1 7.3.1 Handling and Shipping...................................................................................................................7-1 7.3.2 Skidding..........................................................................................................................................7-1 7.4 Assembly Plan ....................................................................................................................................7-2 7.5 Coordination .......................................................................................................................................7-2 7.6 Tolerances...........................................................................................................................................7-3 7.6.1 Fabrication......................................................................................................................................7-3 7.6.2 Vertical Control in the Field...........................................................................................................7-3 7.6.3 Horizontal Control in the Field.......................................................................................................7-3 7.7 Inspection............................................................................................................................................7-3 7.7.1 Grouting of Horizontal Post-Tensioning Ducts..............................................................................7-3 7.7.2 Mechanical Grouted Splices...........................................................................................................7-4 7.8 Backfill ...............................................................................................................................................7-4 7.8.1 Flowable Fill...................................................................................................................................7-4 7.8.2 Compacted Granular Fill ................................................................................................................7-4 PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE viii

7.8.3 Foam Products................................................................................................................................7-4 SECTION 8: CASE STUDY 1, UPTON, MAINE ..............................................................................................8-1 SECTION 9: CASE STUDY 2, BROOKSVILLE, MAINE................................................................................9-1 SECTION 10: CASE STUDY 3, EPPING, NEW HAMPSHIRE .......................................................................... 1 REFERENCES.................................................................................................................................................... R-1 INDEX ..................................................................................................................................................................I-1

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PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE x

INTRODUCTION This guide is the current State of the Art report developed by the PCI Northeast Bridge Technical Committee on the use of Precast/Prestressed Concrete Components to accelerate the construction of bridge projects. The guide will assist designers in determining which means and methods would be appropriate for considering accelerated construction techniques. This guide will offer solutions from deck replacement to total reconstruction of a bridge. Some of the considerations for accelerated construction are: • Improved work zone safety. • Minimizing traffic disruption during bridge construction. • Maintaining and/or improving construction quality. • Reducing the life cycle costs and environmental impacts. Precast components produced off-site can be quickly assembled, and can reduce design time, cost, minimize forming, minimize lane closure time and/or possibly the need for a temporary bridge. In 2002, the PCI Technical Committee developed a report for full-depth precast-prestressed deck panels. This system is used to replace bridge decks during off-peak traffic hours and can be a good solution in terms of minimizing traffic disruption. Prefabrication has also been extended to the bridge’s substructure by means of precast abutments. Several projects in the Northeast have already been built. The use of precast components such as abutments, pier caps, pier columns and precast footings can effectively minimize construction time, traffic disruption and the impact of construction activities on the environment. This guide is organized in the customary order of bridge construction; essentially from the ground up. The manual starts with general information that applies to the whole structure. Following this, the reader will find specific information regarding the different precast components used in accelerated bridge construction. Joints and grouting considerations may then be reviewed as the structures design becomes more defined. The final step then becomes construction. The reader will find recommendations regarding fabrication and inspection of each component used in the structure. Therefore, the reader will find the guide is divided into the following six sections: 1. Application Overview. 2. General Requirements. 3. Precast Components. 4. Joints. 5. Grouting. 6. Seismic 7. Fabrication / Construction. This guide is not intended as a stand-alone document and does not supersede the AASHTO specifications.

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PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE xii


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SECTION 1: APPLICATION OVERVIEW 1.1 WHEN TO USE ACCELERATED CONSTRUCTION Accelerated construction techniques should be used where the benefits of accelerated construction have a positive effect on the construction costs and impacts of the project. In many cases accelerated construction techniques can reduce overall project costs. At this time, the bridge specific costs on small accelerated construction projects are more than conventional construction (This is not necessarily the case with large scale projects.) It is also anticipated that costs will come down as more accelerated projects are let. The savings in accelerated construction projects are found in other aspects of the project such as time, equipment use and labor savings. Decisions to use accelerated construction techniques should be made after considering the following issues: • Temporary Roadways and Bridges • Reductions in Environmental Impacts • User Costs • Political Pressures • Long Detours For additional guidance, refer to the Federal Highway Administration report entitled “Decision-Making Framework for Prefabricated Bridge Elements and Systems (PBES), May 2006”. Accelerated construction should always be considered in cases where temporary bridges and roadways are anticipated. This is especially true where a reasonable detour is available. It may be desirable to close a roadway completely, build the bridge quickly, and live with a detour. In this case, the cost of the accelerated construction is far outweighed by the savings of not building a temporary roadway. Recent accelerated construction projects have shown that commuters and businesses prefer a significant short-term impact over a long-term moderate impact. For bridges over water courses, impacts to the environment can be lessened by the elimination of a temporary bridge. The cost of construction to highway users is significant. Savings to commuters are not typically reflected in construction budgets for highway projects; however there is a significant financial impact to the entire community due to travel delays. In many cases, the cost of accelerated construction techniques can be offset by reductions in user costs. Often the need for accelerated construction can be driven by political pressures. The impacts of construction on commuters and businesses in urban areas can be devastating. Accelerated construction can be used to limit the time frames for construction projects in these areas. On some projects, the use of staging and temporary bridges is not feasible due to limited right of way and environmental issues. In these cases detours are the only option. Accelerated construction techniques should be considered if there are issues with traffic volumes on detours and access for emergency vehicles. Though the intent of this manual is to provide information that applies to precast/prestressed components used in bridge construction, using these components in non-prestress concrete structures is encouraged. The designer may wish to use precast substructure with steel girders and precast deck panels for example.

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1.2 REHABILITATION PROJECTS Many bridge rehabilitation projects may benefit from accelerated construction methods. This guide focuses on precast components that could replace the entire bridge; however portions of existing bridges can also be constructed using these methods. The designer in these cases should balance the cost savings of not constructing new components to the costs of rehabilitating existing components. Costs should include both financial resources and time. 1.3 EXAMPLES OF PREFABRICATED COMPONENTS Prefabricated components in accelerated bridge construction are comprised of separately shipped pieces which are assembled in the field to form a larger structural component of the completed bridge. Figure 1.3-1 and Figure 1.3-2 are examples of what components are used to construct a pier and a bridge deck. Figure 1.3-3 and Figure 1.3-4 further demonstrates the assembly of an abutment structural component and the superstructure. Figure 1.3-5 demonstrates what components are necessary to assemble an integral abutment bridge. Figure 1.3-6 shows the assembly completed.

Pier Cap [ 3.2.4.1 ] Moment Connection [ 4.3.1 ] Anchoring Devices [ 4.3.4 ] Column [ 3.2.3 ]

Footing [ 3.2.1 ]

Figure 1.3-1 Assembly of Substructure Prefabricated Components



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Rail [ 3.5 ]

Deck Slab [ 3.3.2 ]

Girder [ 3.3.1 ]

Figure 1.3-2 Assembly of Superstructure Prefabricated Components

Superstructure [ 3.3 ]

Substructure [ 3.2 ]

Figure 1.3-3 Assembly of Girder Superstructure Structural Component.



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Walls [ 3.2.2 ]

Figure 1.3-4 Assembly of Butted Box Beam Superstructure Structural Component resting on a Cantilever Abutment Substructure Structural Component. Pile Cap [ 3.2.4.2 ]

Post-tensioning Duct [5.4]

Post Tensioning Strands [5.4]

Wall Segments [ 3.2.2 ]

Pile [ 3.1 ] Construction on Piles [ 3.2.1.3 ] Figure 1.3-5 Assembly of Integral Abutment Prefabricated Components.



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Figure 1.3-6 Full Assembly of Integral Abutment Structural Component supporting a Butted Box Beam Superstructure Structural Component.. 1.4 ARCHITECTURAL TREATMENTS An accelerated construction environment does not preclude the idea of having an attractive bridge. In fact the very opposite is the reality. With some careful planning, the resulting bridge can be built quickly, and also be aesthetically pleasing. In most cases, cost will not be a limiting factor. Precast components allow for architectural enhancements at a relatively lower cost than cast in place concrete. All treatments are made at the precast plant where repetitive use of standardized forms lowers the costs to individual projects. Precast plants are well suited for applying aggregate surfaces through means of blasting or the use of retardants. Chapter 5 of the PCI Bridge Design Manual and the Minnesota Department of Transportation’s Aesthetic Guidelines for Bridge Design offer guidance on this topic. These guidelines may be used to proportion components to fit together to meet the function of the structure as well as to enhance aesthetics. 1.5 DEFINITIONS Box Beam – Rectangular shaped beam with a single rectangular shaped void. These beams have depths up to four feet and are used for short to moderate length spans. Prestressed strand is typically placed in the bottom flange in a 2 inch by 2 inch grid. Deck Slab – A solid and very slender slab that may be used for extremely short spans in the longitudinal direction or as a replacement for a cast-in-place deck over girders when placed transverse to the deck beams. Cast-in-Place – Concrete that is formed and placed in the field. Pile Cap – A structural component placed over piles which supports deck components. Prefabricated Component – A part of a larger structural component of a bridge such as a footing, column or PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

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wall. These components are fabricated offsite and shipped in separate pieces to the project site for eventual assembly. Precast Component – A structural component that is cast in a plant and shipped to the project site. Prestressed Component – A structural component that is cast with pretensioned steel strands causing compressive stresses in the component section. The compressive stresses are typically eccentric and are used to compensate for tensile stresses caused by loading of the component. Propriety Precast Products – Precast components that a single entity holds the patents to. These products tend to be specialized and may require special installation equipment or connectors. Accelerated Bridge Construction – A construction process that has been optimized for speed. Structural Component – A major part of a structure comprised of several precast components. Completed abutments or piers are examples of substructure structural components. The completed deck would be a superstructure structural component. Voided Slab – A rectangular beam shape with 2 or 3 circular voids running its length. These beams typically range in thickness from 15 inches to 21 inches. Prestressed strand is typically placed in the bottom flange in a 2 inch by 2 inch grid. Typically, these are used for very short spans.



SECTION 2: GENERAL REQUIREMENTS Guidelines

Commentary

2.1 PARTIAL REPLACEMENT PROJECTS If existing substructure is to be reused, complete dimensions and elevations should be obtained to ensure compatibility with the new precast components.

There is adjustability in precast components; however the tolerances at interfaces are limited. The field survey is recommended.

2.2 DESIGN A prefabricated system is designed using the same design approach as cast-in-place concrete structures.

Providing a safe design to meet the site requirements is paramount in all bridge replacement projects. Designs should not be compromised in order to utilize precast concrete structures. The engineer must focus on ease of fabrication, repetition, and ease of assembly to create a cost effective, precast concrete solution.

In general, the design of precast substructures involves emulation of traditional cast-in-place concrete structures with discrete precast components. The connections between components are designed to emulate traditional construction joints.

Designers should refer to the ACI 550.1R-01, Emulating Cast-in-Place Detailing in Precast Concrete Structures for specifications on emulation design.

Designers may take advantage of posttensioning technologies to facilitate construction of complex structures.

It may be advantageous to design complex structures such as tall piers using post tensioning strand or high strength rods to simplify the connections.

The design and detailing of beams and girders is generally not affected by accelerated construction techniques. 2.3 GEOMETRIC CONFIGURATIONS 2.3.1

Bridge Layout

Non-skewed designs are preferred.


Angles between abutment and wingwalls should be limited to in-line, and 90 degrees. Bridge skew angles should be minimized. In cases where they are unavoidable, the skew angle added to the wing angle should be kept to simple geometric angles such as 30, 45, and 60 degrees. Odd angles will complicate formwork and increase cost.

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2-2

Guidelines 2.3.2

Commentary

Component Sizes and Shapes

The designer should detail components sizes to promote repetition of forming with consideration given to transportation, fabrication and construction.

Battered components should be avoided.

Footing widths may be detailed such that there are common dimensions on each bridge project. For instance on a particular bridge, all footings for wingwalls that are of approximately equal height could be kept identical (dimensions and reinforcing). The economies of repetition may outweigh the perceived benefits of individually sized components. Batters on abutment and wing stems should be eliminated and the overall thickness of the stems should be minimized to reduce the overall weight of the component. Components typically are cast horizontally as slabs.

2.4 TOLERANCES Designers should specify and account for tolerances in layout of components.

All precast concrete products are constructed within a specified tolerance. Designers should refer to the PCI Tolerance Manual MNL 135-00 for guidance on setting appropriate tolerances for each component. Base the layout of components on the nominal center to center of joints as opposed to the actual component size.

Nominal joint widths should be set based on the specified tolerances.

At a minimum, the joint width should account for the width tolerance and sweep tolerance of the components.

2.5 SHIPPING AND HANDLING Precast substructure components should be detailed so that the pieces can be shipped using normal shipping equipment.

The weight of precast substructure components weighing on the order of 30 tons should be anticipated.

In special cases, very large pieces can be detailed; however the shipping costs can be excessive.

It is possible to ship pieces in excess of 30 tons, however the equipment required and limitation of local bridge capacities may limit this. Off-loading of pieces can also be problematic. Larger pieces may be feasible if the pieces can be fabricated in close proximity to the bridge and shipped a short distance.

The designer should consider each State’s requirement for allowable shipping widths.

In general, components should have a maximum width of 12 feet to avoid cost premiums typically associated with shipping of large components over the road. Components PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

Commentary with widths in excess of 12 feet typically require special trucking permits, which can be supplied at a premium.

2.5.1

Lifting Devices

The design and detailing of lifting devices is the responsibility of the fabricator. Lifting devices should be placed to avoid being visible once precast component is placed. Lifting devices that are located in areas that will be visible or exposed to the components should be detailed with recessed pockets that can be patched after installation. The patching material shall match the appearance of the surrounding concrete and provide corrosion protection. See Section 7.2


The designer should specify the level of corrosion protection for lifting devices.

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SECTION 3: PRECAST COMPONENTS Guidelines

Commentary

3.1 PILING The Designer may choose to use Precast prestressed concrete piles as an alternative to steel ‘H’-piles. Consult a Geotechnical Engineer for specific limitations regarding the project site before selecting the pile type and size.

Practice has shown that a minimum of 14 inch prestress pile sections has been successfully used in severe driving conditions. For more information regarding precast/prestressed concrete piles, refer to the PCI Bridge Design Manual BM-02-04 chapter 20.

3.2 SUBSTRUCTURE COMPONENTS Substructure components include footings, wall segments, columns used in piers, and girder support beams. 3.2.1

Footings

The transfer of footing loads to the underlying soils should be made via a grout filled gap below the footings.

It is unreasonable to assume that proper interface can be achieved between compacted soil and a precast component. The unevenness of compacted soil combined with the tolerances of precast will lead to point of localized support. An effective means of providing this support is a grout-filled gap.

The bottom of the footings should be roughened to a ¼” amplitude profile during fabrication. 3.2.1.1 Construction on Bedrock A more extensive soils boring program should precede construction of precast footings so that the degree of variation of top of rock elevations can be assessed prior to construction.

The uneven nature of construction of footings on bedrock may require preparation of the site prior to installation of precast footings. Overblasting of rock by approximately 12” to provide room to prepare for a relatively level work area is PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

As with any construction on bedrock, large variations in rock elevations can affect the layout and design of precast substructure components. It may be desirable to step footings where rock variations are significant. The contractor will also need this information to plan the work. Unknowns in rock elevations are always difficult to address. It is essential that most of this be addressed prior to construction on an accelerated project. The owner should balance the need for more borings with cost constraints. The reason for over-blasting is to ensure that the removal of rock will be a one-time process, and the amount of post-blast clean-up removal will be kept to a minimum.

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3-2


Guidelines

Commentary

recommended. This will facilitate the installation of grout under the footings. See Section 3.2.1.5. Once the area is made roughly level, there are two recommended methods for preparing the area for installation of precast footings. The first is to pour a low-strength concrete sub-footing to provide room for grouting. The second method is to provide small level concrete surfaces under the proposed leveling devices. See Section 3.2.1.4.

3.2.1.2 Construction on Soil Prior to construction on soil, the area must be excavated, and prepared as in normal cast-in-place construction.

The concrete sub-footing need not be high strength. The typical range of footing pressures are magnitudes less than the strength of the subfooting concrete. The sub-footing concrete need not be formed. In most cases, the concrete can be cast against the footing excavation limits. Experience has shown that a low-strength concrete sub-footing does not slow construction and provides a very good work platform for installation of precast components. See Section 3.2.1 commentary.

Once the area is prepared, there are two recommended methods for preparing the area for installation of precast footings. The first is to pour a low-strength concrete sub-footing to a level that is just below the proposed bottom of footing elevation as shown in Figure 3.2.1.2-1. The second method is to provide small level areas under the proposed leveling devices. See Section 3.2.1.4. Temporary load distribution plates will be required under the leveling devices when a subfooting is not used in order to spread the loads to the soil.

Figure 3.2.1.2-1 Placing footing segment on a sub-footing.



Guidelines

Commentary

Figure 3.2.1.2-2 Completed footing. 3.2.1.3 Construction on Piles Construction on piles will in general follow the guidelines for construction on soil. A concrete sub-footing may be used, or the footing can be temporarily supported on load distribution plates on soil.

See Section 3.2.1 commentary.

Provisions should be made in the footing design for grouting of the areas around the pile tops. Grout placement is demonstrated in Figure 3.2.4.2.1-1 with an integral abutment section. A footing slab would be similar. 3.2.1.3.1 Construction Clearances Provide clearance around each pile to account for driving tolerances.

Six inches minimum clearance is recommended. Refer to state standards for additional guidance.

3.2.1.4 Leveling Devices Leveling devices are critical in maintaining proper vertical grade control on precast concrete substructures. Cast-in embedded leveling devices should be used to allow for adjustment of the footing grade and elevation during installation.

Experience has shown that these leveling devices provide fast and easy grade adjustment at a minimal cost. The use of leveling shim packs is discouraged since there is no way to adjust the grades without removing the component.

A minimum of four leveling devices should be specified for each spread footing component. Each device should be designed to support half the self weight of the footing component.

During installation, there is a tendency for the piece to rock on the diagonal corner supports, therefore each device should be designed to support half the weight of the component.

The component should be leveled prior to release of the piece from the crane. A thorough greasing of the leveling device is recommended.

The effort to adjust the leveling devices is greatly reduced if the component is partially supported by the crane, or if it is greased.

Figure 3.2.1.4-1 shows a leveling screw detail. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

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3-4

Guidelines

Commentary

Once the installation of the component is complete, the leveling bolt shall be backed out and the shaft filled with grout. 4"Ø BLOCKOUT

REMOVE BOLT AFTER BASE HAS BEEN GROUTED. TAPERED BLOCKOUT

GROUT BLOCKOUT AFTER REMOVAL OF BOLT

1"Ø BOLT PIPE SLEEVE

REINFORCING WELDED TO SUBFOOTING OR STRUCTURAL FILL LEVEL CONCRETE SUPPORT 3" MIN. GROUT BED

LEDGE

Figure 3.2.1.4-1 Leveling Screw Detail 3.2.1.5 Grouting Under Footings The purpose of grouting under spread footings is to distribute the foundation pressures from the precast footing to the underlying soil or rock. A gap that is grouted is recommended to achieve this. Exact grouting methods can be left up to the discretion of the general contractor. The plans and specifications should give certain guidelines on grouting procedures. See Section 5.

There are several methods that have been successfully used. The contractor should be allowed to use a method that best suits the experience of the workers and the available equipment.

The strength of the grout is secondary to its ability to properly fill the gap under the footing.

Footing pressures are magnitudes lower than the compressive strength of grout; therefore strength of grout is not a concern. A minimum grout strength of 1000 psi is recommended.

The grout should be placed in the void through ports cast in the footing. Attempting to flow the grout from one side to another is not recommended unless the footing is relatively narrow.

Placement may be accomplished by pumping or gravity feed through grout ports. The ports should be arranged so that the grouting operation progresses in a single general direction to avoid air pockets.

3.2.2

Wall Segments

There are several wall options available to designers for accelerated construction projects.

Designers should refer to each State’s specifications for a listing of the approved PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

Commentary

Many States maintain approved proprietary precast concrete retaining wall systems. Another option is to use a precast concrete cantilever wall. The following options should be evaluated for each wall:

proprietary walls.

Precast Cantilever

Cantilever retaining walls can be detailed using the techniques outlined in this guideline. The wall stems and footings can be made with precast concrete components. Often this type of wall will use the least amount of width (normal to wall face) when compared to other proprietary retaining wall systems.

Mechanically Stabilized Earth (MSE)

Using precast facing panels in a MSE wall is an ideal solution for accelerated construction. The wall facing, reinforcing strips and backfill can be constructed concurrently.

Precast Concrete Modular Block Gravity Wall

A precast concrete modular block gravity wall is another ideal solution for accelerated construction. The blocks interlock using keys cast into them. The dead weight of the blocking system along with the interlocking keys eliminates the need for mechanical connections between precast units.

Figure 3.2.2-1 Placement of an abutment segments.


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Guidelines

Commentary

Figure 3.2.2-2 Precast abutment with pin connection.

Figure 3.2.2-3 Fully assembled abutment. 3.2.3

Columns

3.2.3.1 Round vs. Rectangular Round columns should be avoided. Rectangular columns should be specified for bridge structures.

Round columns are difficult to fabricate. These will likely have to be poured vertically which may prove to be difficult in a precast plant. This will likely result in higher component prices. Rectangular columns can be poured on their sides. Several can be poured at the same time – side by side. This can enhance the efficiency and therefore reduce the cost of the component.

3.2.4

Girder Support Components

Precast components can be used to distribute girder loads to foundations. The most common components are as follows: PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines 3.2.4.1 Pier Caps A Pier Cap is a beam that spans the columns it is being set upon. The cap can be connected to the columns by either grouted mechanical splices or post tensioning. 3.2.4.2 Integral Abutment Pile Caps Pile Caps are typically used in integral abutment bridges. Though pile caps may also be used as piers supported on a line of piles as well. These are set over a line of piles then grouted. The tolerance for this construction is the same for footings. See Section 3.2.1.3. An example of a pilecap in an integral abutment structure can be seen in Figure 4.3.3-1.

Figure 3.2.4-1 Assembly of a pier cap.

Figure 3.2.4-2 Pier Construction. 3.2.4.2.1 Construction on Piles Placing a pile cap over piles requires similar details and tolerances as footings set on piles. See Section 3.2.1.3. Grout placement is demonstrated in Figure 3.2.4.2.1-1 with an abutment section.


Commentary

3-7


3-8

Guidelines

Commentary

Grout

Packed Gravel, Sub-Footing or

Concrete Flow

Figure 3.2.4.2.1-1 Concrete flow in Abutment Section

Figure 3.2.4.2.1-2 Completed integral abutment assembly. 3.2.4.3 Seat Adjustment Beams Seat adjustment beams may be precast according to field measurements. These beams may be used to elevate existing beam seat elevations on existing abutments. The beams are set on elastomeric sheets placed on the existing abutment. Figure 3.2.4.3-1 demonstrates the use of a seat adjustment beams to fill a portion of the abutment where deeper steel girders once sat.



Guidelines

Commentary

Figure 3.2.4.3-1 A Seat Adjustment Beam was placed on this abutment to level the bearing seats for the new deck units on this bridge rehabilitation. 3.3 SUPERSTRUCTURE COMPONENTS 3.3.1

Girders and Beams

Girders or beams shall be designed and detailed according to conventional methodology. Refer to the PCI Bridge Design Manual. 3.3.2

Full Depth Deck Slabs

Prefabricated decks offer advantages for deck construction since bridge components can be prefabricated offsite and assembled in place. Other advantages include removing the deck placement from the critical path of bridge construction schedules, cost savings, and increased quality due to controlled factory conditions. See Figure 3.3.2-1 .Figure 3.3.2-2 shows a typical placement of deck slabs. Re-decking with prefabricated modular deck panels is a viable method of deck replacement that minimizes traffic disruption. More importantly, this construction method allows opening part of the bridge under construction to traffic. In addition, nighttime re-decking with prefabricated concrete modular panels, although slightly more costly than daytime re-decking, can further minimize interruption of traffic. Also, the existing composite concrete deck could be replaced in stages. In each stage, a portion of the transverse section is removed and replaced along the full length of the bridge, while other lanes are maintained open for traffic.


General information on full depth deck slabs is presented here. For more information, refer to “Design Guidelines for the use of Full Depth Precast Deck Slabs used for new construction or for replacement of existing decks on bridges.” This document is available at the PCI Northeast website (www.pcine.org).

3-9


3-10

Guidelines

Commentary

Figure 3.3.2-1 Schematic of precast deck assembly

Figure 3.3.2-2 Placing Deck Slabs 3.3.3

Stay-in-Place Forms

In situations where a cast-in-place deck will be necessary, precast stay-in-place concrete panels may be used to save time during construction. These panels do not require the extensive shoring and carpentry that conventional wood forms PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

3-11

Commentary

require, nor do they need to be removed once the deck has cured. Refer to the Precast Deck Panel Guidelines from PCI-NE. 3.4 PROPRIETARY BRIDGE SYSTEMS The use of proprietary bridge systems should be considered as an alternative for accelerated bridge construction when the following situations arise: 1. Construction is limited to a complete bridge replacement only. Line and grade will remain unaltered. 2. The time period for design and construction is limited.

Complete bridge systems are proprietary systems that can meet the needs of a design-build project. The bridge system may include precast footings, abutments, wingwalls and the deck and include all the connecting hardware. Some systems have arches rather than abutments and a deck.

3.5 BRIDGE RAILING The designer may use any available rail system that meets the State’s and AASHTO requirements. In addition to existing rail alternatives including steel, aluminum and cast-in-place concrete, the designer should also consider precast rail systems. Refer to section 4.3.4 regarding details for anchoring precast rail to the deck.

Figure 3.5-1 The Northeast Precast Concrete Rail


The Northeast Precast Rail was designed and tested using a static load test conforming to AASHTO TL-3 requirements. See Figure 3.5-1 .

3-12




4-1

SECTION 4: JOINTS Guidelines

Commentary

4.1 GENERAL Joints fall under two categories. The first are structural connections that transmit moment, axial or shear forces between components. The second are non-structural connections that may be used for thermal movements or to separate discrete portions of the structure (e.g. abutment to wingwall joint). 4.2 LAYOUT OF JOINTS In general, the designer should show proposed layout plans of all joints that form connections in the structure. This layout plan will be used as a guide to determine sizes of components and general construction sequencing.

Full height components with vertical joints are typically preferred over components that are “stacked” with horizontal joints. However, horizontal joints may be incorporated in a design if the weight or size of the pieces is excessive.

The designer should include contract provisions that allow different joint configurations within contract defined boundary conditions. Figure 4.2-1 shows the minimum recommended distance between footing and wall joints. Figure 4.2-2 shows the potential layout of joints in a typical abutment.

Locations and configuration of joints should be the contractor’s option based on boundary conditions set by the designer.

CL FOOTING JOINT CL STEM JOINT 1'-6" MIN AND MIN OF 2 MECHANICAL SPLICES FOOTING 8"

ABUTMENT OR WINGWALL

GROUTED SPLICER (TYP) 2"

FOOTING

Figure 4.2-1 Vertical Joint Offset Plan Detail


Examples of boundary conditions are as follows: • The designer may specify that a vertical joint be placed away from bearing locations • The designer may specify a minimum width of components • Horizontal joints may not be allowed near normal water levels • Stage construction joint locations may need to be specific


4-2 A

PILASTER (TYP)

CONSTRUCTION JOINT

CONSTRUCTION JOINT

BEARING SEAT

APPROXIMATE EXISTING GROUND

FILL LINE

4" Ø WEEPER (TYP

OPTIONAL CONSTRUCTION JOINTS

GRANULAR BACKFILL 2V:1H (TYP)

STRUCTURAL FILL (2' THICK)

FLOWABLE GROUT BED (3" MIN.)

A

Figure 4.2-2 Abutment Elevation Showing Layout of Joints 4.3 STRUCTURAL JOINTS 4.3.1

Moment Connections

Components can be connected with a joint that can transmit moment and shear using the following methods. See section 5.2.1.3 for grouting procedure. • Embedded Mechanical Couplers as shown in Figure 4.3.1-1 . 2"

STEM WIDTH

8" MECHANICAL GROUTED SPLICES

1 1/2 "

FILL WITH APPROVED FLOWABLE NON-SHRINK HIGH STRENGTH GROUT

The most common connector is a grouted sleeve for mild reinforcing that can develop in excess of 125% of the specified yield strength of the bars. See ACI 550.1R-01, Emulating Cast-inPlace Detailing in Precast Concrete Structures. For grouting sequence see section 5.2.1.3.

6" TOE FOOTING

2'

HEEL FOOTING

6" x 6" PLASTIC SHIM AT EACH END OF ABUTMENT COMPONENT

Figure 4.3.1-1 Stem Joint Detail • Cast-in-place closure pours

Closure pours are also effective; however speed of construction is compromised. This is often used for horizontal moment joints.



4-3

CAST-IN-PLACE CLOSURE POUR NARROW CLOSURE POUR WITH GROUTED SPLICERS PRECAST SECTION

Figure 4.3.1-2 Cast-In-Place Closure Pour • Post Tensioning with match-cast components. See Figure 4.3.3-1.

The designer shall address shear transfer through moment connections.

Separate unit

Post Tensioning may be used for complex structures (tall piers), or to eliminate closure pours for horizontal moment connections (integral abutment stems, pier caps, etc.). In these cases the components are match cast against each other during production and an epoxy adhesive is placed between the components during installation. See Figure 4.3.1-2. Shear transfer can be accommodated by the use of grouted shear keys within the joint, keyed pockets, or by providing additional reinforcement across the joint (shear friction design).

Placing units together

Units connected

Figure 4.3.1-2 Example of sections that were match cast for a tight fit. The right photo shows the sections held together by the use of an epoxy adhesive. 4.3.2

Shear Connections

Certain components may need to be connected with a joint that only transmits shear using the following methods: • Vertical Grouted Keys as shown in Figure 4.3.2-1 and Figure 4.3.2-2 . PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

Vertical shear joints are typically used in tall vertical wall joints and transverse joints in one-


4-4

way footing designs. SHEAR KEY FILLED WITH APPROVED NON-SHRINK GROUT

1½"

6 ½"

1 ½"

D

3½" 1" CHAMFER 6 ½"

(TYP)

1 ½"

1"

Figure 4.3.2-1 Footing Joint Detail 1½

1/3

1 (TYP

1" (TYP

SHEAR KEY FILLED APPROVED NON-SHRINK

1/3

W

GROUT

1/3

3½

Figure 4.3.2-2 Detail of a Vertical Joint in Wall • Horizontal Grouted Keys as shown in

Horizontal shear joints are typically used in column to bent cap. Shear transfer can be developed by means of a grouted shear key within the confines of the joint.

Bent

Horizontal Grouted Joint Mechanical Splice

Shear Key

Column

Figure 4.3.2-3 Horizontal Grouted Joint • Reinforced Dowels as shown in Error! Not a valid bookmark self-reference..

Shear transfer can be developed by means of steel reinforcing bars or grouted mechanical splices designed for shear friction. An example PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


of this would be an approach slab to abutment connection. The detail shown is one state’s typical approach slab. Other state details will vary. For instance, some states do not require a concrete overlay and others place the approach slab at the roadway surface. CLOSED CELL EXPANSION C L BRG

CONCRETE OVERLAY

JOINT MATERIAL FILL VOID WITH AN APPROVED GROUT

ROADWAY SELECT MATERIALS

BOX BEAM

JOINT FILLER BURIED APPROACH SLAB

SLEEVE

BEARING PAD 1'-0"

9"

#5 ANCHOR DOWEL

4" 10 ½" ½"

½” CLOSED CELL FILLER MATERIAL

Figure 4.3.2-4 Beam End Detail with Approach Slab 4.3.3

Pile Connections

Integral abutment pile connections can be achieved by providing a blockout in the precast component. This connection should be designed to develop the full moment capacity of the pile. Refer to Figure 4.3.3-1. The connection for pile supported spread footings can be achieved by providing a blockout or recess in the precast component. This connection may be designed to develop the full moment capacity of the pile. The connection will also depend on the need to prevent uplift on the piles. See Figure 4.3.3-2 and Figure 4.3.3-3. The size of the blockouts accommodate pile driving tolerances.

needs


to

The designer should refer to individual state construction specification tolerances.

4-5


4-6

Abutment and Wing segment mild reinforcement for temperature shrinkage, handling, and wing parapets

C L Brg. Slope to Match cast joints quantity and location vary as required

Bridge Approach Slab Galvanized metal duct with deformations refer to design considerations

Galvanized deformed anchor sleeve Galvanized corrugated fill/vent sleeve refer to design considerations Galvanized thread bar post tensioning refer to design considerations

Pile Abutment & Wing Shear Reinforcement

Redundant Void Location to be filled

Figure 4.3.3-1 Typical Integral Abutment Details

3/8 " Stone Concrete Tapered grout port at each pile 2" gap over pile Extend grouted dowels from Pile into footing 1'-0“ Leveling bolt

Min.

Precast concrete pile

Note: Steel pile details are similar. Weldable reinforcing steel bars can be field welded to the pile web after installation.

Figure 4.3.3-2 Conceptual Elevation Pile Supported Precast Footing With Uplift On Piles



4-7 3/8 " Stone Concrete Grout port at each pile 2" gap over pile

1'-0“ Leveling bolt

Min.

Precast concrete pile

Figure 4.3.3-3 Conceptual Elevation Pile Supported Precast Footing Without Uplift On Piles 4.3.4

Anchoring Devices

Certain components will need to be connected to others with pre-embedded anchoring devices. Pre-embedded anchoring devices will require additional quality control measures in the precast plant to ensure the anchored component fits up to the anchoring component. To ensure accurate anchor layouts, anchor templates should be used. Another recommendation is to dimension anchor locations using running dimensions all measured from a common point.

Though not required, having the same precast plant fabricate both the anchored component and the anchoring component will better ensure that each will fit up to the other.

In general, field drilling of anchors is not recommended.

There is a high potential for conflicts with internal reinforcements. If field drilling is used, care should be taken in the layout of reinforcement to prevent conflicts.

Examples of anchored components are: • Bridge rail connections Bridge rail will require anchors to be previously embedded in the precast component or bridge deck. Depending on the type of rail, different measures should be employed to ensure a durable connection. Figure 4.3.4-1 shows the detail used to anchor the Northeast Precast Rail. See Section 3.5. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

A precast concrete rail system may require measures such as: • Setting the rail on a raised pedestal. Water and other corrosive materials will flow along the edge of the pedestal and not seep in the joint of the rail and the deck sections. • Stainless steel anchoring bolts. • An elastomeric bearing pad for the rail section to set upon.


4-8

Stainless Steel Bolt, Plate Washer and Anchor Bolt

Rail Base

Rail Pedestal

• A steel rail system may require galvanized or stainless steel plates and anchor bolts.

Elastomeric Bearing Pad

2” Above Wearing Surface

Deck

Figure 4.3.4-1 Bridge Rail Anchor Detail • Beam Bearing Assemblies The preferred method for supporting precast components is to set the beams on elastomeric bearings without anchorages at each bearing. Lateral forces can be resisted by discrete keeper blocks, abutment backwalls, or cheek walls. See Section 7 for more information.

Tight tolerances or other construction concerns may require the keeper block to be placed and connected after the beams or girders are placed.

Certain conditions may require the use of bearing assemblies.

Bearings and bearing assemblies for precast beams and girders should not differ from conventional bridge construction.

4.4 NON-STRUCTURAL JOINTS Non-structural joints in substructures are primarily intended to allow for thermal or differential settlement movement of the adjacent sections of the structure, and to provide fabrication and construction tolerance. These joints do not transfer moment, axial or shear forces between adjacent components. See Figure 4.4-1

In most cases, these joints should be sealed to prevent moisture from penetrating the area between components where freezing action could spall the adjacent components. In some cases, the joints can be left open.

Examples of non-structural joints include retaining wall expansion and contraction joints, joints between different substructure units (abutment to wingwall interface), and joints in long pier bents (where effects of thermal movement can cause large internal frame forces). Non-structural joints may also be desirable between substructure sections that may potentially experience differential settlement. An example of this would be the interface between a pile supported integral abutment and a long ushaped wingwall supported on spread footings. Sealing of the joint can be accomplished by injecting a foam sealant in the opening. The rear face of the wall may be sealed with a membrane sheet, however foam fill is recommended near the ground line or water line. Grouting is also an acceptable option. See Section 5.2.


GUIDELINES FOR ACCELERATED BRIDGE CONSTRUCTION USING PRECAST/PRESTRESSED CONCRETE COMPONENTS 1½ "

FILL WITH CLOSED CELL MATERIAL AFTER SETTING STEMS WALL STEM

STEM WIDTH

WALL STEM

BACKER ROD

Figure 4.4-1 Non-structural Vertical Joint


4-9

4-10




SECTION 5: GROUTING Guidelines

Commentary

5.1 SUB-FOOTINGS Typical cast-in-place (CIP) concrete placement techniques and mix designs for footings are usually more than adequate to support the proposed loadings.

Plans should detail a roughened surface.

CIP concrete can be used to level an irregular surface, such as bedrock. The assembly plan should detail the compressive strength requirements as required to support the anticipated load from the leveling screws. See Section 7.4. The top surface should be roughened (raked, broomed, etc.) to improve sliding resistance.

The sides of the pour need not be formed. The concrete may be cast against the excavation. 5.2 COMPONENT TO COMPONENT GROUTING It is the Contractor’s responsibility to determine the specific type of grout to be used in each joint, and the methods of installation based on the notes on the plans and in the specifications.

The assembly plan developed by the contractor should specify the type of grout and method of installation for each joint. See Section 7.4.

A pre-packaged, shrinkage-compensating, flowable, grout is recommended for most connections. The strength of the grout should be equal to or greater than the strength of the joined components. 5.2.1 Horizontal Surfaces

The designer should include a note on the plans or in the specifications describing the required properties of the grout in each connection.

5.2.1.1

Area Below Precast Footings

Figure 5.2.1.1-1 shows the assembly of an abutment wall and footing. 5.2.1.2

See Section 3.2.1.5.

Recessed Key Connection

This joint is typically found at the stem/footing joint in abutments. Use of a recessed key will improve the shear capacity and will create adequate head to help push a flowable grout through the joint minimizing the need to pump the grout into place. Figure 4.3.1-1 shows an example of the recessed key.


The grout placed within this joint contributes to the compressive side of the moment couple resisting overturning loads. It also provides corrosion protection for the connections within the joint. Prepackaged grout shall be mixed according to manufacturer’s recommendations.

5-1


5-2

Guidelines

Commentary CL BRG.

GRANULAR BACKFILL

LEVELING SCREW (TYP.)

2V : 1H (TYP) 2'-0" STRUCTURAL FILL (SHOWN) OR 1'-0" SUBFOOTING CONCRETE ON 1'-0" STRUCTURAL FILL

1'-0" (TYP) 3" GROUT BED

Figure 5.2.1.1-1 Abutment Section 5.2.1.3

Recommended Grouting Procedure

Step 1: Fill the key to just below the lower port of the grouted mechanical splice (see Figure 4.3.1-1 ). The grout should be installed by pouring the grout into the key from the front face of the vertical component and moved through the joint to the back-side of the key to promote complete filling of the joint. This procedure should be started at one end of the joint and proceed continuously along the joint.

Filling this joint from both sides and both ends simultaneously will increase the chance for a void within the key. Pumping the grout into place should be encouraged as it supplies a continuous flow of grout making it easier to maintain a continuous flow through the key.

The grout placed in step 1 shall be kept out of the mechanical splice by the use of a washer or stopper.

Washers placed over the rebar extensions provide the seal to keep the mechanical splice free of step 1 grout. See Section 5.2.3.

Step 2: Grout the mechanical splice. Step 3: Fill the remainder of the key. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

5.2.1.4

Commentary

Non Recessed Connection

This connection does not use a key. See If shear and/or compression transfer is required through the grout, the grout should be a structural, non-shrink material. See Section 4.3.2.

This joint is typically found in horizontal connections between components where there is significant load transfer. This grout may take many forms including pre-packaged grout, dry pack, pre-placed pre-packaged mortar (buttered), or grout placed under pressure.

The grout placed within this type of joint should also provide protection from the environment (freeze/thaw, corrosion, etc.).

The designer should choose the most appropriate type of grout for the anticipated exposure conditions.

5.2.2

Vertical Surfaces

A flowable, cementitious grout should be used for vertical joints. It should be introduced at the top of the joint, filling it from bottom to top.

This surface is most typically found between vertical wall components. Significant hydraulic head will be created due to the typical height of the joints being filled. Backer rods placed at the extremities of the joint will not be . Supplemental formwork will be required to resist grout pressures and prevent blowouts.

If shear transfer is not required, consider filling this joint with expanding foam sealant or other fillers.

This treatment may be considered adequate if the joint is deemed non-structural. The expanding foam keeps the joint free of foreign material and should be supplemented with a flexible joint sealant (both sides) and membrane on the fill side for waterproofing. (See Figure 4.4-1 ) There are other specialized products such as a plastic bag which is inserted in the joint and then filled with grout.

Pre-applied rigid joint filler materials are not recommended. Inserting rigid fillers after assembly is also not recommended.

Experience has shown that tolerance between the components will be compromised, which makes component assembly virtually impossible. Installation of fillers after assembly results in a poor quality joint.

5.2.3

Mechanical Grouted Splices

Only grout specified by the mechanical splice manufacturer should be used. The type of grouting operation is usually dependent on the orientation of the sleeve. A training session on proper grouting techniques should be required for field personnel. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

A sleeve cast in the upper component is a postgrouted connection. The grouting operation takes place after the upper component is in place. Grout is typically hand-pumped into the lower

5-3

5-4


Guidelines

Commentary port filling the sleeve from bottom to top. Manufacturer recommendations shall be followed. The manufacturer will typically require special equipment to mix and install the grout. The amount of grout being pumped into a sleeve should be watched closely to detect any excess which indicates a void in the key grouting job. If this occurs care must be taken to fill the void which normally can only be done by pumping through a sleeve inlet hole. A sleeve cast in the lower component is a pregrouted position. The sleeve is filled with grout from the top and the ports are plugged after the sleeve has been purged of air. The upper component is lowered into position and the bars extending from the component are pushed into the sleeve displacing the grout into the surrounding joint.

5.3 PILE CAPS Self-consolidating concrete is recommended to fill the void around the piles. The concrete should either have limited shrinkage characteristics or be made with a shrinkage compensating admixture. Refer to Figure 4.3.3-1for more detail on the pile void.

These connections are typically at integral abutment caps, pile bent caps, or pile supported footings. Self consolidating concrete is used to ensure adequate consolidation without segregation around the piling.

The concrete should be placed through fill ducts into pile blockouts. Vent ducts shall also be provided into the blockout. When fill and vent ducts are used they should be corrugated. At least one fill and one vent duct should penetrate into each pile blockout.

Having two ducts per blockout allows for concrete to be placed in one duct, while placement is being monitored in the other duct.

5.4 POST TENSIONING DUCTS Grouting of post tensioning ducts should be done using a grout designed for pressure grouting the annular spaces around post tensioning bars or cables.

There are several grouts available that are designed for this purpose. These grouts have been designed to be pumped through small annular spaces over long distances without segregating. If a grout is used that has not been designed for this purpose it is likely that the aggregates will segregate and result in plugging the grout ports, lines or pump, and possibly compromising the grouting operation.

Post tensioning ducts should be corrugated metal and kept to the minimum size practical while still allowing adequate room for

Using a corrugated duct in combination with a grout allows the post tensioning tendon to become developed along its length in the event of any loss PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

Commentary

construction tolerances.

of end anchorage due to corrosion. The designer should select a duct size and grout that is consistent with the grout manufacturer’s recommendations. In most applications allowing a total of ¾” of tolerance should be adequate. (for example using a 3 inch duct for a 1-3/8” post tensioning bar)

Special care should be taken for grouting of ducts in either vertical or sinusoidal patterns.

There have been problems with excess bleed water in post tensioning ducts that have led to severe corrosion of the tendons. These problems primarily occur at high points in duct runs.

5.5 BLOCKOUTS FOR ANCHORING DEVICES Blockouts are used to recess bolting mechanisms such as those for post-tensioning strands in butted beam decks or for the anchoring bolts in precast rail. All open blockouts on the structure shall be filled with a stiff non-shrink grout. First ensure the recess is free of dust and other construction debris. Apply the grout using a trowel into the recess in layers to ensure the cavity is completely filled. The final layer shall be troweled smooth with the face of the component. The grout color and texture shall closely match the component.


5-5

5-6




SECTION 6: SEISMIC CONSIDERATIONS Guidelines

Commentary

6.1 GENERAL CRITERIA In general, the design and details of precast concrete components for seismic forces should be consistent with cast-in-place concrete construction.

All provisions specified in AASHTO need to be satisfied in a precast concrete bridge. This includes but is not limited to reinforcing steel in footings, column confinement, and connections between the superstructure and substructure. The process of designing seismic reinforcement is the same as for a cast in place concrete structure. Slight variations in detailing may be required because of the use of precast components. These issues are covered in this section.

6.2 CONNECTION OF SUPERSTRUCTURE TO SUBSTRUCTURE There are several methods of connecting normal stringer bridges to the substructures. In most cases, these connections are designed to transmit the lateral seismic forces from the superstructure to the substructure. It is also possible to make the connection integral.

6.2.1

In most states, the connection of the superstructure to the substructure is detailed as a pinned connection. Integral connections are also specified, but are not as common. There are other options for seismic restraint such as cable restrainers and seismic isolation devices. These methods are also acceptable; however they are not included in this document.

Keeper Blocks

Keeper blocks consist of concrete keys that are placed between two interior beams to transmit lateral forces from the superstructure to the substructure. Keeper blocks are often the most cost effective means of restraining a bridge for seismic events.

Keeper blocks are usually only used for lateral seismic forces. Longitudinal seismic forces can be resisted by the abutment backwall, or anchor rods.

Bridges should be designed with only one keeper block per superstructure unit.

Concrete keeper blocks have very low ductility. If two blocks were detailed, it is likely that one would carry all the seismic demand. Distribution of seismic forces to other keeper assemblies would most likely only occur after failure of the first keeper.


6-1


6-2

Guidelines

Commentary

If keeper blocks are precast, the connection of keeper blocks can be made using several of the methods outlined in this document.

Keepers can be installed using grouted mechanical splices, or can be cast integral with the precast substructure component.

Consideration should be given for casting keeper blocks in place. 6.2.2

Pilasters

Pilaster are used on adjacent box beam bridges near the fascia beam ends. They resist lateral seismic forces. The design of pilasters is similar to keeper blocks. Each pilaster must be capable of resisting the entire lateral seismic force at each substructure unit, since only one pilaster will engage the superstructure at a time. 6.2.3

See Section 4.3.4.

Pilasters are usually only used on adjacent box beam bridges since there is no gap between adjacent beams. On stringer bridges, keeper blocks are probably more cost effective, since only one keeper is required to resist lateral seismic forces in both directions. The commentary from Section 6.2.1 is also applicable to this section. Also, see Section 4.3.4 for information on pilasters.

Abutment Backwall

Longitudinal seismic forces can be resisted by the abutment backwall. The design of abutment backwalls for seismic forces is similar to keeper blocks.

The design of seismic restraining systems is based on limited and repairable damage. Using backwalls for restraint will inevitably result in a structure that has shifted longitudinally during the seismic event. The structure may need to be jacked back into position after seismic events.

Designers should verify that the distance between the backwall and the beam/slab is sufficient for thermal movement, but small enough so that the beams do not slide off the substructures.

One of the most important aspects of seismic design is to prevent superstructures from sliding off foundations. This issue becomes more pronounced on multiple span bridges where all joints between spans are assumed to be closed in one direction.

6.2.4

Anchor Rods

The design of anchor rods for lateral load should take into account the bending capacity of the rod, edge distance to the concrete foundation, internal reinforcing around the embedded portion, strength of the concrete, and group action of the rods.

The AASHTO specifications do not address the design of embedded anchors loaded in shear. Designing for the shear capacity of the rod is not acceptable. The rods tend to fail in combined bending and crushing of the concrete around the rod. The American Concrete Institute publication “Building Code Requirements for Structural Concrete (ACI 318-02) is recommended.

Anchor rods should be designed to be ductile. The use of high strength heat treated rods is discouraged due to low ductility.

During a seismic event, it is inevitable that only a percentage of the rods will initially see load due to construction tolerances. Ductility in the rods will ensure that all rods will work PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

Commentary together to resist seismic forces.

The embedded portion of the rod shall be properly reinforced in order to prevent brittle fractures of the surrounding concrete.

The anchor rods should normally be surrounded by lateral reinforcing steel near the surface of the concrete. This will allow lateral forces to be resisted after the initial cracking of the concrete.

Material for anchor rods should be ASTM F1554, and should be either threaded (with nuts) or swaged on the embedded portion of the rod. The design yield strength of this material may be specified as36ksi (250MPa), 55ksi (380MPa), or 105ksi (725MPa), depending on the design. The yield strength should be given in the specifications or on the plans.

This material is specifically designed for anchor rod applications. Other materials have been used, but do not offer the economies of ASTM F1554. The designer should offer options of swaging or threading the anchor as different suppliers supply one or both of these options.

6.2.5

Integral Connections

Superstructure can be connected to substructures using integral moment connections. In most cases, this connection will be made with a cast-in-place closure pour or by using grouted mechanical splices.

The most common form of integral connection is between beams and abutments in stringer bridges. In these cases, the end diaphragm is usually cast in place between the beams due to the complexity of the shapes. Integral connections have successfully been made between beams and abutments using grouted mechanical splices cast into the beamends.

6.3 COLUMN CONNECTIONS Columns are often the most heavily loaded components during a seismic event. Special care shall be taken to properly detail connections in precast column components. 6.3.1

In high seismic regions, columns are designed to form plastic hinges and contribute to dissipation of seismic forces. The high demand region on a typical column is at the ends where the column connects to the footings and pier caps.

Column Base and Cap Connections

Moment connections can be made in precast column components by using grouted mechanical splices for longitudinal reinforcing steel confined by transverse reinforcing steel.

The FHWA has recently approved grouted mechanical splices for use in seismic column connections in low to moderate seismic zones. Research in Japan has shown that the grouted mechanical splices can fully develop the longitudinal reinforcing bars as well as contribute to shifting the plastic hinge away from the extreme end of the column.

Grouted mechanical splices are capable of developing 125% reinforcing steel yield strength.

The 125% development is normally required for all mechanical reinforcing couplers. Some


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Guidelines

Commentary

These devices are different than a lap splice. The strength of the splice is not dependent on the concrete surrounding the sleeves. Therefore limitations for locations of lap splices in should not be applicable to mechanical connectors.

states require at least 150% of the specified steel yield strength of the bar for splices in plastic hinge zones. Some grouted mechanical splices can also achieve this level; however this must be specified in the contract.

According to the current AASHTO codes, mechanical splices should be staggered a minimum of 24” for bridges in high seismic zones. (Section 7.6.2, Div IA of the Standard Specifications and Section 5.10.11.4.1f of the LRFD Specifications).

This requirement is partially due to concerns about the effect of the mechanical splices on the location and stiffness of the plastic hinge zone. High seismic zones are defined as Categories C and D in the Standard Specifications and Zones 3 and 4 in the LRFD Specifications. One way to achieve this is to put ½ of the mechanical splices on one side of the connection and ½ of the mechanical splices on the other side of the connection. Another way to accomplish this is to place the mechanical connectors within the footing where plastic hinging is not a factor; however the pier cap connection should be staggered as noted above. The AASHTO specifications for low to moderate seismic zones allow for splicing 100% of the longitudinal bars with mechanical splices at one location. The details in this guideline are based on nonstaggered mechanical grouted splices, since the majority of the bridges in the US are in low to moderate seismic zones. Designers can modify the details in this document to satisfy these requirements for higher seismic zones.

6.3.2

Splices Along Column Length

The connection of column-to-column splices is similar to that used for column-to-footing and column-to-cap connections.



Guidelines 6.3.3

Commentary

Confinement Reinforcement

It is possible to provide confinement for longitudinal reinforcing in precast concrete columns. AASHTO provisions for confinement based on cast-in-place concrete construction should be followed. Longitudinal bars can be confined with transverse ties detailed in accordance with the AASHTO code.

Transverse ties need to be properly detailed in order to achieve confinement. The following is an excerpt from Section 6.6.2. Division IA of the 17th edition of the “Standard Specifications for Highway Bridges: “Transverse reinforcement shall be extended into the top and bottom connections for a distance equal to onehalf the maximum column dimension but not less than 15 inches from the face of the column connection into the adjoining member.” The same section also states: “A closed tie may be made up of several reinforcing elements with 135O hooks with a six-diameter, but not less than 3 inch, extension that engages the longitudinal reinforcement.” These provisions do not require the confinement steel to pass through the joint between the column and pier cap or footing. It is acceptable to properly terminate the transverse tie confinement steel at the end of the column, and also in the adjoining member.

6.4 FOOTINGS The design of precast footings for seismic forces should follow normal procedures for cast-in-place concrete footings. 6.4.1

Internal reinforcement

Column confinement reinforcement shall extend into the footing as noted in the AASHTO design specifications. 6.4.2

Refer to the discussion in Section 6.3.3

Pile Uplift

Special details are required to provide pile PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

See Figure 4.3.3-2. Note that this detail is

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Guidelines uplift capacity in precast footings. methods are available:

Commentary Several

conceptual and is based in an interpretation of the AASHTO code. The committee is not aware of any projects where this detail has been used.

Reinforcement from concrete piles (precast or cast-in-place) can be extended into pockets in the precast footing. This reinforcement can also be installed on the top of the pile by drilling and grouting.

Reinforcement for concrete pile uplift should be similar to cast in place footing construction.

Weldable steel reinforcement can be welded to the top of steel piles after cut-off. These bars can be extended into pockets in the precast footing.

It is important to use weldable reinforcement when making welded connections.

Pockets for uplift reinforcement should be tapered to provide wedging effect with the surrounding precast concrete. The pockets should extend through the footing to facilitate grouting.

Tapered pockets have been successfully used for the connections between full depth precast slabs and stinger beams. The tapered pocket can transmit the uplift force to the precast footing without relying solely on the bond of the grout to the precast footing.

The size of the pocket should be kept to a minimum so that pile compression can be transferred as well.

The pocket size should be just large enough to account for the size of the reinforcing, but allow for bearing of the pile on the precast footing. The location of drilled bars (concrete piles) or welded bars (steel piles) should be adjustable so that the pile driving tolerances can be accounted for in the connection. The drilled bars can be located anywhere within the center core of the concrete pile. The steel bars can be welded on either the web or flanges of the pile. Minor bending of the welded bar is also acceptable. The uplift bars will most likely need to be installed before the footing is set; therefore care should be taken in determining the location of the bars so that the footing pockets line up with the bars.



SECTION 7: FABRICATION/CONSTRUCTION Guidelines

Commentary

7.1 CONTRACTOR OPTIONS 7.2 LIFTING DEVICES The location and design of lifting devices is the responsibility of the precast manufacturer. Locations that are visually sensitive should be identified on the contract drawings. Lifting devices should not be used in these areas if possible. Lifting devices in these areas need to be recessed, easily removed, and patched to match the surrounding concrete. 7.2.1

Corrosion Protection

Provisions shall be made to protect the device from corrosion when the device is to be exposed to the environment in the finished construction.

While some lifting devices may be located in areas that will be hidden, most will need to be removed. This will likely result in a portion of the lifting device being exposed. The exposed steel will in time allow corrosive materials to leach into the concrete. To prevent this, the contractor should apply a patch to seal the exposed steel from corrosion. Lifting devices that will remain in place in highly corrosive environments (such as parapets) may require the use of galvanized steel or stainless steel. This approach is very expensive and not recommended for substructure components.

7.3 EQUIPMENT 7.3.1

Handling and Shipping

The size of precast components should be finalized by the precaster and contractor with consideration for shipping restrictions, equipment availability and site constraints. The final component sizes will be shown on the assembly plan. 7.3.2

Most components can be shipped on flat bed trailers. Unusual trailer configurations and support frames should be avoided unless the quantity of pieces justifies the special equipment.

Skidding

On certain substructure units, it may be PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

It has been proven that structures with weights

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Guidelines

Commentary

desirable to assemble the entire structure or a portion of the structure adjacent to the final installation location and jack it horizontally into its final position. This should only be considered for complex locations where traffic disruption is very limited.

as high as 6 million pounds can be skidded into place using specialized skidding equipment, hydraulic jacks, or cable systems. This is very expensive specialized work; therefore it should only be used in areas where the time of changeout from an old structure to a new structure is very limited.

7.4 ASSEMBLY PLAN This plan is created by the Precaster and Contractor and submitted to the Owner for approval. It provides detailed information on the Contractor’s means and methods for assembling the components.

The assembly plan is one piece of a project delivery concept devised for accelerated bridge construction. This concept allows the Owner to design the structure and gives the contractor the ability to decide the most suitable means to assemble the components.

The assembly plan should at the very least, include all information required to complete the work such as: • Engineer of Record for the assembly plan. • Shop drawings of all components. • Specific product names and other material requirements for all grout products proposed for use. • Proposed method of erection and the amount and character of equipment required. • Temporary support requirements for substructures including leveling screws and/or shims and lateral load and moment resistance requirements for vertical components during assembly. • Component assembly sequence. • Tolerance requirements for the assembly of the components. • Grouting plan.

The contract drawings provide a design and standard details for joints within the structure and performance requirements for materials that are used to assemble the components.

7.5 COORDINATION Coordination between all parties is paramount with accelerated construction.

The importance of establishing lines of communication between all parties involved cannot be overstated. The decision makers in each discipline must be identified early, and they must be available by phone to make timely decisions when things don’t go completely as planned.



Guidelines

Commentary

7.6 TOLERANCES 7.6.1

Fabrication

Fabrication tolerances shall be according to standard precast practice. See PCI MNL-116, Manual for Quality Control for Plants and Production of Precast and Prestressed Concrete Products or PCI MNL –135-00 Tolerance Manual for Precast and Prestressed Concrete Construction for more detailed tolerances for precast components. Tolerances for project specific requirements should be detailed in the project specifications. 7.6.2

Vertical Control in the Field

Horizontal joints shall follow appropriate tolerances to ensure final elevations are as specified on the contract plans.

7.6.3

Errors in horizontal joints will accumulate with each joint. The designer should limit horizontal joints to as few as possible. Horizontal joints should be detailed to allow for minor adjustments as required during construction.

Horizontal Control in the Field

Gaps between adjacent wall components should provide for fabrication and construction tolerances. Contractor should survey and layout location of components prior to installation. Layout control should continue throughout assembly.

Grouted shear keys can be introduced as required to provide additional fabrication and assembly tolerances if needed.

7.7 INSPECTION 7.7.1

Grouting of Horizontal Post-Tensioning Ducts

The post-tensioning duct grout should be mixed according to the grout manufacturer’s published mixing instructions.

In order for the grout to work properly it must be mixed to the consistency intended by the manufacturer.

Sufficient grout should be on site to completely grout an entire unit prior to commencing the mixing of any grout.

Particular attention should be paid to the published recommended pot life of a mixed batch of grout. Once the process of grouting has begun it must continue without interruption until it is complete, or there is a risk of leaving ungrouted ducts, or portions thereof, in the completed work.


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Guidelines

Commentary

Grouting of post-tensioning ducts should be done from one end only.

Grouting should be continuous from one end of the post-tensioning duct, and should be continued until grout flows from the grout port at the opposite end of the duct being grouted.

7.7.2

Mechanical Grouted Splices

A template will be required for accurate mechanical splice placement during component fabrication and/or field cast conditions to ensure component compatibility.

Templates should be used during fabrication to ensure fit-up between joined components. Proper dowel extensions are required to develop the full capacity of the grouted mechanical splice. Placement tolerances should be as recommended by the mechanical splice manufacturer.

The grouting process should follow the manufacturer’s published recommendations for materials and equipment.

A minimum of two inspectors should be required for the mechanical splice grouting operation: one to watch the grout preparation and one to watch the grouting process.

7.8 BACKFILL The plans and specifications should allow for contractor alternates for backfill materials. The plans should indicate which of the backfill options are acceptable for each substructure unit. 7.8.1

In many cases, there may not be an obvious solution to the most cost effective backfill material. Contractor alternates will facilitate the most cost effective solutions.

Flowable Fill

This material has the ability to rapidly backfill a structure without the need for compaction. The designer should investigate the effects of the flowable fill on the substructure.

Flowable fill can be installed quickly, however it has several drawbacks. The actual material is more expensive than granular fill, and the area to be filled will need to be secured with either formwork or embankments. In some cases, the cost of these items may outweigh the cost of compacting traditional granular fill. Flowable fill will exert significant fluid pressure on the substructure prior to setting. This loading condition should be checked in the design, if flowable fill is specified.

7.8.2

Compacted Granular Fill

Normal compacted granular fill may be used for backfilling operations. 7.8.3

Foam Products

Foam products can be used to facilitate backfilling operations. These products consist of

Stacking of these blocks can progress very fast. These blocks are normally supplemented PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


Guidelines

Commentary

lightweight (3 pcf) polystyrene blocks that are stacked behind a substructure unit.

with flowable fill and/or granular backfill.

The designer should investigate the effects of this material on the design of the substructure since the unit weight is much less than traditional granular backfills.

The light unit weight may affect the design of structures where the dead load of the backfill is used to counteract overturning forces.

The elevation of the water table should also be studied since these products can float.

There are two issues with these products. First, the compressive strength of the blocks is limited; therefore a layer of granular material above the blocks will be required in order to distribute the wheel loads to the blocks. Second, the designer should investigate floatation of the blocks in areas where the water table is above the bottom of the blocks. Often the buoyancy can be offset by the weight of the granular fill over the blocks. Another problem is that polystyrene blocks tend to be very reactive to petroleum products. In some cases, polystyrene blocks can dissolve rapidly when in contact with petroleum fuels. Caution should be used when installing in locations where fuel is stored.


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SECTION 8: CASE STUDY 1, UPTON, MAINE

CASE STUDY 1 East B Hill Road in Upton, Maine


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INSTANT BRIDGE – JUST ADD WATER Nathaniel D. Benoit, PE, Maine Department of Transportation, Augusta, ME Eric T. Calderwood, PE, Calderwood Engineering etc, Richmond, ME Wayne L. Frankhauser, Jr., PE, Maine Department of Transportation, Augusta, ME Dennis R. Hanson, EIT, Technical Construction Inc., Turner, ME Kenneth R. Heil, PE, Figg Bridge Engineers Inc., Exton, PA Jeffrey J. Tweedie, PE, Maine Department of Transportation, Augusta, ME

ABSTRACT This report is a case study on a project under taken by the Maine Department of Transportation in 2004. In September of 2004 the Maine Department of Transportation completed construction of the Andover Dam Bridge in Upton, Maine. The design of the bridge consists of a 65-ft single span, precast, butted box beam superstructure, founded on pile-supported, integral abutments. The bridge is located on a local road in rural Maine, and the use of a long detour and rapid bridge construction techniques were determined more cost effective than the use of a temporary bridge. For this project the use of self consolidating concrete combined with a precast concrete substructure and superstructure enabled the bridge to be constructed while the road was closed for a total duration of 96 hours. This case study discusses the background information, specifics of the new construction, traffic considerations, construction sequence, precast components, and lessons learned by the Department during the construction of this project.

Keywords: Rapid Bridge, Precast Substructure, Integral Abutments, Self Consolidated Concrete



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INTRODUCTION In 2003 Maine Department of Transportation needed to replace an 18 ft wide posted bridge on the East B Hill Road in Upton, Maine. The existing bridge was a pony truss that had been strengthened with steel kickers from the abutments up to the first panel point, at a later date MaineDOT Bridge Maintenance had further stiffened the truss with the addition of two rolled beams at the roadway grade which were then connected to the truss floorbeams. A new, wider structure, capable of carrying all legal loads was needed. Due to the remote location, long detour, small traffic volume, and cost of a temporary bridge, the project was identified after preliminary design as a potential candidate for the implementation of rapid bridge technology. With the national move, and all the hype concerning rapid bridge construction, it became apparent to MaineDOT that it was only a matter of time before the driving forces of traffic concerns and environmental impacts would require the use of expedited construction techniques. MaineDOT was interested in using techniques that could be easily evaluated and duplicated or modified to suit other bridge construction projects. The effectiveness of the techniques would need to be evaluated both from the standpoint of cost savings, or lack thereof, and for its feasible use in other similar applications.

BACKGROUND Maine was looking for a location to try a rapid bridge construction project, but one that MaineDOT could undertake on its own terms. Andover Dam Bridge in Upton, Maine crosses a pristine stream that is home to native brook trout. The site is relatively remote and shrouded in spruce trees. While there are only approximately 120 vehicles per day, a significant number of them are logging trucks. The destination of most vehicles is either the famous fly fishing on the Rapid River, as this is the easiest access point to the Pond in the River, or the Andover Wood Products Mill, one of the major employers in the Andover area. Any shut down of the East B Hill Road would result in a 55 mile detour (see figure 1), which would directly affect both delivery of logs to the mill, and travel time of workers at the mill who live on the other side of the bridge. Limiting the closure time to a matter of days would be a real benefit to the users of the East B Hill Road. Yet with only 120 vehicles per day if unforeseen consequences delayed the project there would not be a tremendous public outcry. The site was the perfect location to attempt rapid construction. Contracting Techniques combined with precast concrete superstructure, substructure and approach slabs were seen as the keystones to decreased construction time. The elimination of a temporary bridge limited the right of way takings required, as well as the clearing for temporary approaches. It was estimated that a temporary bridge at this site would cost approximately $75,000 and the anticipated savings would be used to finance an incentive for early completion. Both the incentive and disincentive would need to be sizable to cover the contractor’s additional cost to accelerate the work. Precast concrete superstructures have a long history of rapid fabrication and erection in the State of Maine and MaineDOT was very comfortable with their use on a span such as this one. Precast substructures were a new element to add to the equation, but without them it would have been impossible to reduce the road closure to much less than 40 days.


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Figure 1 MaineDOT had experimented with a project similar to this the year before when they eliminated the temporary bridge and coupled that with a long detour. The biggest difference was that cast in place abutments were used, and the road was closed for approximately 45 days. This project had to take that next step, and reduce or eliminate any formwork, stripping and curing to be done in the field.

SPECIFICS OF NEW CONSTRUCTION The bridge in preliminary design was a very different structure than the one that was eventually to be constructed. Initially the proposed structure was a 65 foot prestressed precast butted box beam superstructure with a leveling slab, waterproofing membrane, and bituminous wearing course founded on spread footings on dense native soils. Although this was the optimum substructure unit given the site specific soil conditions, MaineDOT Bridge Maintenance prefers integral abutment type structures because they have no joints and PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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therefore ease the maintenance of the structure. Because of this preference coupled with site specific scour concerns the decision was made to make the change to integral abutments founded on driven H-Pile. This opened the door to facilitate the implementation of rapid bridge technology. The leveling slab on the box beams was eliminated; the crown of the roadway was introduced in the abutments. The abutments and approach slabs would have to be precast in order to eliminate concrete curing times in the field. The abutments would be in segments to reduce their weight and bond outs would be provided to allow the driven H-Pile to penetrate into the abutment (see figure 2 for abutment configuration). Concrete could then be placed around the piling through fill sleeves to each bond out and the segments would then be post tensioned together. The new abutments were located sufficiently behind the existing abutments such that the piling could be driven behind the abutments, cut off below grade, and the existing abutments could then be backfilled again to carry traffic on the old bridge while new equipment was brought in to erect the superstructure and substructure units (see Figure 4 for construction sequence).

Figure 2

Several factors would determine the geometry of the precast abutment segments. Conceptually the units would be required to: 1. have sufficient post tensioning to carry the passive earth pressure required of integral type abutments 2. be light enough to ship and handle PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

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3. have bond outs of sufficient size to allow for out of position piling, and the cumulative effects of several pile out of position 4. have joints that are impervious to water flow Due to a layer of boulders and cobbles, pile driving required pre-excavation through the boulder and cobble layer. Given the consistency of the remaining material through which the pile would need to be driven, coupled with MaineDOT’s construction experience, a practical out of position limit of 6” around each pile was used to develop the pile bond outs within the abutment sections. After cutoff, a 1” plate (see Figure 3) was welded to the top of each pile to facilitate bond with the concrete to be cast through the fill sleeves in the abutments. Conceptually it was anticipated during the design phase that the precast segments would bear directly on these bearing plates; however the contractor proposed supporting the bottom of the abutment with a steel frame welded to the piling. The bottom of the precast abutment segments would set the vertical control for the entire bridge. This had the advantage of allowing some additional vertical tolerance in the bond outs for the piling, as well as being easily adjustable in the field during the initial closure period. Using a 14 inch H-pile section with 6 inches of tolerance for out of position piling led to a bond out dimension of 26 inches square. Leaving 11 inches for the minimum wall thickness at the bond out sections yielded a total abutment width of 48 inches (see figure 2 for abutment geometry). To facilitate fabrication and shipping, each abutment was to be cast in two separate pieces, an A segment and a B segment. Each segment weighed approximately 33 Tons. Shear keys were constructed between the Figure 3 A & B segments, and the segments were match cast against the mating segment. A structural adhesive epoxy was applied to each joint prior to post tensioning the abutment segments together; this provided a waterproof bond at the match cast joint between the segments. Six 1-3/8” diameter galvanized post tensioning bars would become the main reinforcing steel within the abutment components and carry the full passive pressure of the backfill during thermal expansion cycles maintaining a minimum of 100 psi of compression at the joint. Self consolidating concrete, modified with a shrinkage compensating admixture, was placed through fill sleeves in the abutment. This assured adequate consolidation around piling sections and completed the connection of the abutment segments to the piling. Facets of the superstructure were customized to allow rapid construction as well. Neither a structural slab nor a leveling slab were considered because setting up screed rails, casting, and curing them would unnecessarily slow down construction. The crown of the roadway then had to be introduced into the structure at the abutments. In order to achieve the proper roadway profile a shim course of pavement was placed between the base course and finish course. The additional dead load of the shim course was accounted for during the design of the superstructure. The initial plan called for the construction of permanent curb and railing during single lane closures during the day after the new bridge was opened to traffic, but the contractor opted to precast the curb sections on the beams. This saved time and cost and allowed the permanent railing to be installed without the need for temporary traffic barrier except at the ends of the structure. The shear keys between boxes were wider than MaineDOT’s standard width, and were filled using a self consolidating concrete modified with the addition of a shrinkage compensating admixture. This allowed the shear keys to be grouted very rapidly. In order to facilitate a rapid closure the approach slabs could not be cast in place either, but were in fact precast in 4 sections and pitched to drain runoff away from the structure in both directions. (A below grade approach slab is the preferred method of constructing approach slabs in Maine.) Traffic was allowed directly on top of the precast units. Waterproofing membrane and bituminous pavement were applied during single lane closures after the structure was opened to traffic. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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CONSTRUCTION SEQUENCE The contractor was given 192 hours of total allowable closure time. The number of closures and duration of each were left to the contractor to decide. In order to ensure the closure was limited to the minimum time required an incentive of $200.00 per hour was offered if the closure took less than 192 hours. An additional incentive of $10,000 was provided for simply meeting the 192 hour deadline. The incentives were combined with a graduated disincentive beginning at $300.00 per hour and ending at $600.00 per hour for each hour the road was closed in excess of the allowable 192 hours. In order to be effective the incentive and disincentive had to be by the hour, if we had used a per day rate it would be easy to use the whole day once a part of it had been used, but using a per hour rate made it even more imperative to make the road opening requirements very clear to the contractor. THREE INITIAL CLOSURE PERIODS The first closure period was used to remove obstructions to pile driving and install the driven H-pile at abutment #1. The pre-excavation was required to be moderately deeper than shown on the plans, and although we came close to the water table, we were not required to drastically modify the construction procedure with the addition of a separate cofferdam, pumps and sedimentation basins. Once the pile driving was complete the driving frame was welded to the driven pile at exactly the proposed elevation of the bottom of the abutments. This would serve to support the abutment segments during the final closure. Careful measurements to each pile were taken from the centerline of construction. These would be used during fabrication of the abutments to verify the locations of the bond outs in the precast units. The elevation to remove the existing abutment to was carefully located on the abutment face. This would be used later to perforate the abutment facilitating easy removal during the final closure. The installation of piling went over without incident, and the native soils were placed back into the hole and compacted adequately to open the road to traffic. The total road closure period for the first closure period was 12 hours.


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Figure 4 The second closure period was used to remove obstructions to pile driving and install the driven H-pile at abutment number two. Although, after the initial closure’s success, spirits were high it became apparent early on that we would not be quite so fortunate on the second day. Once the hole was opened up and we excavated below the existing road gravel, the excavator began to take out buckets full of nothing but rock, we had found the remains of the bridges namesake, the Andover Dam. Nonetheless we were fortunate not to find any log crib below the stone, or what our biggest fear was, below the existing abutment. Once we had excavated through the obstruction layer we found that the existing abutment had a heel that projected into and interfered with the pile driving locations. The contractor had to get a Hoe Ram on site. At this point it was clear that we would not be driving pile today. The pile driving subcontractor had serious, well founded, safety concerns regarding driving pile after dark, and we would therefore have to fill the excavation with material through which we could drive the pile up to the bottom of the new abutment location. The remainder of the hole was filled in with native soils and compacted sufficiently to open the road to traffic. The total road closure period for the second closure was 12 hours. The third closure period was used to complete the preparatory work at abutment number two. The existing abutment had been marked during the previous closure to indicate when we could stop digging. The pile driving frame was installed and the piles were driven to the required resistance, although one of the pile encountered an obstruction causing it to deviate significantly from its theoretical position, it was pulled and restarted several times with the same results. Finally, although not exactly in the right position the last pile was driven. Careful measurements were taken to the actual piling locations. The frame was then erected and welded to the piling at the exact elevation required for the bottom of the abutments. Native materials were used to backfill the existing abutment and the road was opened to traffic. The total road closure period for the third closure was 12 hours. SIX WEEKS OF PREPARATION During the 6 weeks following these initial closure periods, preparations were being made to facilitate an expedited schedule during the last closure period. The existing abutments were perforated with two inch diameter holes at a two foot spacing located at the required cutoff elevation. While this did not impact the structural capacity of the existing bridge it facilitated easy removal during the fourth and final closure. Granular backfill and riprap were stockpiled just off site. Coordination between the contractor and his subs and suppliers was critical. Everything had to come together at the same time. The Abutments were under fabrication. No modifications were required at the bond out locations for abutment #1; abutment #2 was moderately modified to better reflect the actual location of the driven H-pile. The pile that had encountered an obstruction that altered its final location was out of position by exactly the six inch tolerance that we had allowed for in the bond outs. While theoretically it would be possible to erect the segments if they were constructed as designed, we decided to shift the bond out for that piling sufficiently to allow the greatest flexibility in the field. Once all the preparations were made, materials stockpiled, concrete trial batched, precast concrete boxes and abutments were all fabricated and were either delivered or on the road. The stage was set for the fourth and final closure. THE FINAL CLOSURE PERIOD The first day of the final closure period was full of activity. Work was taking place on both sides of the river simultaneously. One large excavator worked at removing the soil down to the driving frame, carefully uncovering it to reveal the support for the abutment segments at abutment #1. Simultaneously, a second excavator removed the grade beams and concrete deck from the truss. A hydraulic crane set up to place the abutment segments at abutment #1. At this point it was critical that the segments be erected at abutment #1 early PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

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in the day to allow the crane time to break down and travel all the way around the detour in order to be prepared to set the abutment segments at abutment #2. The abutment segments were erected very smoothly, and post tensioning began immediately. Once the post tensioning was complete, backfill was placed carefully on both sides of the abutment keeping the elevation approximately the same so as not to shift its alignment at all. The existing truss was removed and the old abutments were removed to their final elevations, 1 foot below the finished slope line. Riprap was placed in areas that would be located underneath the new superstructure. Self consolidating concrete was placed through the fill sleeves to permanently connect the abutment to its foundation piling. The first day was complete after about 14 hours of the final closure period. The second day of the final closure was similarly exciting. Abutment #2 segments were placed and post tensioned. Abutment #2 was backfilled, and self consolidating concrete filled the pile bond outs. Rip rap was placed in front of abutment #2. The precast box beams were erected, and the hydraulic crane was broken down and sent home. The second day of the final closure period was complete after about 38 hours of the final closure period. The third and final day of the final closure cleaned up most of the details. The approach slabs were set at the appropriate grade, the precast box beam superstructure was anchored into the abutments, lateral post tensioning strands between box beams were installed, and the shear keys between the box beams were filled with self consolidating concrete. Bond outs in the curb were filled with the same concrete mix. Bridge rail was installed, gravel was placed and the approaches were graded, and the structure was opened to traffic. The final closure period lasted a total of 60 hours. The total elapsed road closure time for the bridge replacement was only 96 hours. FINAL COMPLETION Several elements were then completed under traffic with only single lane closures. This included grouting the post tensioning tendons within the abutments, installing waterproof membrane and bituminous pavement, grouting the post tensioning pockets. Completing the approach work also was done under traffic.

LESSONS LEARNED MaineDOT learned several lessons during the construction of the Upton Andover Dam Bridge. Operations taking place simultaneously tend to be extremely equipment intensive, and there is a tremendous amount of real estate required for lay down areas, storage, and equipment in order to keep multiple operations going simultaneously. Plan on separate closures for pile driving and make sure there is plenty of room behind the existing abutments to avoid piling and the bottom of a battered mass concrete abutment sharing the same physical space. Take more borings than you think you need, because once the road is closed you are committed. Keep the details simple and clean, nothing fancy. Don’t pin the box beams to the abutments, pin the approach slabs instead. Don’t be tempted to reduce the incentive, or to cut the allowable closure time significantly, because it must be possible for the contractor to achieve a bonus significant enough to account for the additional expenses of accelerating the work.

CONCLUSIONS The experimental rapid bridge in Upton, Maine was a very successful project and will lead to the use of similar techniques on other bridge replacement projects where a reduction in traffic disruption is beneficial. MaineDOT was initially concerned that even though we would be eliminating a temporary bridge with significant cost PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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associated with it, the accelerated schedule, incentive, and precast substructure would drive the cost above that of a more conventionally constructed bridge. That concern proved to be unfounded, and although it is difficult to say for certain, it’s generally agreed within the Department that the project resulted in a cost savings. Part of the reason for this may lie in the equipment intensive operations which lend themselves well to rental equipment. Additionally, when the construction duration is limited, the contractor has less overhead cost associated with the project. The environmental benefits seem to be very promising. The area which would have been cleared and used for temporary approaches to a temporary bridge could remain wooded. Areas that were destabilized by excavating for the new abutments were completely stabilized with the final rip rap placement the same day. The excavation only stayed open for a matter of hours. While vehicular travel time was significantly impacted during the closure periods, people had sufficient advanced warning and could plan their schedules accordingly. They did not seem to mind the bridge closing for a few days. MaineDOT has realized that rapid bridge construction can save the state money and limit inconvenience for the traveling public. In a state where much of the economy is dependent on tourism it is sometimes beneficial to shift the disruption caused by construction to a period more acceptable to the local business community. MaineDOT has already put these same techniques to work on two other projects which are under construction during the writing of this paper. Both of these projects have more significant traffic volumes and are in more prominent locations. Although this is not going to become the standard construction methodology in the state, it is going to be another tool that the bridge designer can have in his toolbox to be applied in the right circumstances to save money, traffic disruption, and environmental impacts.


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SECTION 9: CASE STUDY 2, BROOKSVILLE, MAINE

CASE STUDY 2 Davis Narrows Bridge in Brooksville, Maine


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Davis Narrows Bridge in Brooksville, Maine: Fast Track Solution to and Environmentally Sensitive and Tourist Location

M. Asif Iqbal, P.E. Maine Department of Transportation Augusta, Maine

ABSTRACT

The unique features of the existing Bridge, the sensitive environmental habitat, and the tourist attraction at the Davis Narrows Bridge over the Bagaduce River in Brooksville, Maine created a set of issues that demanded a fast track approach to bridge design and construction. The Maine Department of Transportation after considering several options decided to custom design a single span bridge using all precast elements. The Precast abutments and wingwalls were designed as post-tensioned units over driven piles to reduce excavation, forming and curing time, and to eliminate the use of cofferdams. Extensive geotextiles were used to stabilize the causeways and reduce impacts to Eelgrass patches. The new abutments were installed behind the existing granite block abutments to avoid changes to hydraulics favored by locals and tourists. Precast Box-beams were erected efficiently using a launching girder. The entire project from demolition of the existing bridge to pavement and guardrail installation on the new 89 foot, $1 million Bridge was completed in only 30 days. The ease with which the bridge was constructed not only impressed the locals but also the Contractor and the Owner.



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INTRODUCTION

The Davis Narrows Bridge spans the Bagaduce River and connects the towns of Penobscot and Brooksville along the rugged coastline of Downeast Maine. The bridge site posed a number of challenges due to its unique wildlife habitat, pristine waters, local oyster farm, tourism, poor sight distance, and long detour to mention a few. These issues motivated the Maine DOT to consider a fasttract and low-impact design that would not only address the issues at hand but also one that would prove to be an effective solution to similar problems at other locations.

The existing Bridge was constructed back in 1941 using painted rolled steel beams on dry laid granite blocks. The granite blocks were constructed on rock fills that form the 100 foot long causeways on both approaches leading to the bridge. The paint on the beams had failed and corrosion was hastened by the salt water underneath. The FHWA Sufficiency Rating had dropped to only 31. It was thus programmed for replacement in the 2004-2005 Work Plan.

The causeways create a constriction on the daily tide cycle which in turn produces a hydraulic head of about three feet in each direction at the abutments between high and low tide. The rapids from this phenomenon have become one of entertainment value on which many tourists and locals ride their kayaks and inflatables during the summer months. The locals were thus not in favor of changing any of the hydraulic characteristics.

The Bagaduce River near the Bridge site is also one of few areas in Maine where the Horseshoe crab breeds. The Horseshoe crab is an ancient creature that is said to predate the Dinosaurs by 100 million years. Another concern was the presence of Eelgrass on two corners of the bridge. Eelgrass, which is a salt water seagrass, is protected by the Federal Clean Water Act. It provides natural habitat and food to marine organisms. The Bagaduce Watershed Conservation Association had requested the complete transplant of Eelgrass that would have been affected by the causeway riprap. The Maine DOT biologist was able to precisely mark the Eelgrass patches on survey plans using backpack GPS units. Prior to construction, these patches were hand transplanted by divers and volunteers.

The bridge site is also a natural fishing ground not only for the local people but also for cormorants, larks, and the Blue Heron besides other species of birds. Throughout the construction, these birds provided a natural sight for the construction crew. The oyster farmer just upstream of the bridge had requested that the silt and sediments from the construction be reduced to an absolute PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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minimum. This was achieved by using precast abutments instead of cast-in-place which significantly reduced equipment movement, excavation, and flow of any concrete into the tidal area. Use of precast units for abutments also eliminated the need for cofferdams which would have disturbed the river sediments. The use of silt booms at both abutments was all that was needed with the precast system.

Given the sensitive nature of the project surroundings, the design team considered the options available and decided on an all-precast system to quickly install the bridge, address the issues at the site, and open the road to traffic in the shortest time possible.

BRIDGE DESIGN AND CONSTRUCTION

The bridge was designed by the Maine DOT Bridge Program design team during the winter of 20042005 according to AASHTO LRFD Bridge Design Specifications. Some of the precast features were conceived from the Andover Dam Bridge in Upton which is the only other bridge in the state with precast abutments. The new bridge is single span, 89 feet long and 32 feet wide with integral abutments. The design theory for the precast abutment was based on using conventional integral-abutment dimensions and then splitting the abutment into segments that can be easily transported and erected. Since the abutment units are supported on piles, the entire abutment needed to act as a single unit which was accomplished by post-tensioning the units with threaded bars. The project was advertised in May of 2005 and awarded to Reed and Reed Inc. contractors of Woolwich, Maine in July, 2005 for a total bid price of $1.06 million. All precast abutment units and box beams were manufactured by Strescon Ltd. of New Brunswick, Canada. The construction was expected to be quite challenging because the work schedule needed to be synchronized with the daily tide cycles. The Maine DOT principal designer also spent the entire 30 days of bridge closure at the construction site to help address issues as they came up. The project was completed 5 days ahead of the allotted 35 day closure.

The details of the

construction process are given below.

Abutments and Wingwalls

Since the hydraulics of the bridge could not be changed, the existing granite block abutments could not be removed entirely. As a result the new integral abutments were designed twelve feet behind the existing abutments (See Figure 1-3). It would have been nearly impossible to drive conventional PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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steel sheet-pile cofferdams because of the rocky river-bottom and the long causeway that allowed significant flow of water through them. As a result, the excavation for the abutments was done within controlled embankments and at low tide. Silt booms were used on the outside to reduce seepage of silt and sediments. The dimensions of the precast and post-tensioned abutment units are similar to that of conventional cast in place integral abutments in Maine.

The integral abutments of the bridge are supported on four piles which are driven to bedrock (See Figures 2, 5). Light I-beams were placed transversely on each side of the piles to ensure that the abutments were seated level. The HP 14x89 piles were one size heavier than required to account for some section loss due to salt water conditions. The piles are expected to be wet at all times. The abutments consist of two 16 foot long precast center units and two 4 foot long precast extended wing wall units. All contact surfaces were specified to be match cast at the precasting plant and coated with epoxy concrete adhesive just prior to post-tensioning in the field. All four units are post-tensioned (PT) together with six threaded bars. The PT bars were designed to resist biaxial loads on the center units from traffic and earth pressure, and cantilever loads on the wingwalls due to earth pressure. The match cast joints also consisted of four shear keys to help align the precast units during erection. Voids were designed into the abutment units to receive the piles. These voided areas were enlarged to reduce the shipping weight of the precast units. Once the abutments were lifted into place and the post-tensioning was completed, the voids were filled with Self Consolidating Concrete (SCC) through six inch ducts on top of the abutment units. The six PT ducts were pumped with conventional grout. The final lock off tension in the PT bars was designed to prevent any cracks due to Service Loads. Although the PT bars provided bending resistance, the steel reinforcement in each unit was designed for deep beam bending action, and punching shear resistance over the voided areas. All steel reinforcement in the abutment units were epoxy coated.

Only the small tapering top portions of the wingwalls that abut the box beams were cast in place. This was necessary to obtain a tight fit of the beams against the abutments. The use of precast abutments significantly reduced impact to the river and tidal areas, and reduced the construction time by a third.

Superstructure and Approach Slabs

The superstructure is made of eight butted Precast Pre-stressed Box Beams (B-II 48) that were PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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post-tensioned transversely to act as a single unit (See Figure 4). They were delivered three per day which was also the beam erection rate. A 110 ton and an 80 ton crane erected the beams in place. The contractors were very innovative in their approach to erecting the box beams. The heavy beams would have required widening the causeways with temporary fills to swing the beams into place and thereby causing significant impact to the natural habitats. This was eliminated by the use of custom made steel launching beam with a trolley supported on Hilman rollers. The contractors used the truck that brought the beams to back-up the beams across the channel thereby eliminating the need to lift an entire beam off the truck with one crane. The use of pea stone concrete mix in the shear keys instead of the conventional sand grout reduced the possibility of discharging material into the river. As an additional measure, the foam backer rods in the shear keys were bonded to the beams prior to erection and then compressed into place during erection of adjacent beams.

Transverse post-tensioning strands were located at five points along the length of the beam. Although the designers intended the curbs to be precast with the beams, it was determined that cracks would have developed during transportation through the rough local roads. Thus the curbs were cast in place, and this operation started as soon as only two beams were erected. The precast approach slabs were erected next and these were positively connected to the abutments using six #6 loops providing longitudinal restraint to the beams. The loops were placed through pockets in the approach slabs and into precast holes in the abutment units. The pockets were later filled with sand grout. All steel reinforcements except for the pre-stressing strands were epoxy coated.

The use of precast pre-stressed butted box beams significantly reduced erection time. Substantial time was also saved by not having to construct a leveling slab. High Performance Membrane was torch-applied on the beams by a subcontractor followed by a three inch Hot Mix Asphalt pavement.

PROJECT SCHEDULE AND COST

The contractors were given a total of thirty five days of road closure to complete the project with incentives of $1000 per day and equal disincentives. They decided to work on causeways leading to the bridge first and then close the bridge for completing the rest of the project. The causeways were built back in 1941 with massive rocks and boulders that allowed significant flow of water through them. To reduce impact to existing flow characteristics, the new approach roads on the causeways were built on choke stone layers stabilized with high-flow geotextiles. This took three weeks to complete followed by PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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the bridge closure on September 6th, 2005.

The first week of closure was used to remove the tops of the existing abutments followed by excavation at the new abutment locations. The second week was used for driving the piles and erecting the abutments. Some time was lost when two of the pile locations were blocked by large boulders in the excavation. The contractors did not claim addition time because the presence of boulders was clearly indicated in the boring logs. The contractors brought in a larger excavator to removes the large boulders. The four precast units that make up an abutment took only two hours to erect and post-tension. The grouting operation was done the following day at low tide. During the third week, the beams were erected using a steel launching beam structure and a crane on either end. The curbs were constructed as soon as the first fascia beam and an adjacent beam were in place. The wingwall tops were cast early fourth week followed by installation of bridge rail and application of the high performance membrane. The heavy cranes were also disassembled during this week and removed from site. Pavement was applied during the last two days leading to bridge opening. The bridge was opened to traffic on October 5th, 2005. The approach guardrails were installed during the two days following the bridge opening and no lane closures were needed due to the low traffic volume at that time. The contractors also left the site four days after the bridge was opened to traffic.

The Davis Narrows Bridge was constructed on a very unique site which posed some significant construction challenges. The structure itself is one of a kind and as such the cost of this bridge cannot be easily compared to other bridges in Maine. The unit cost of the structure itself was $233 per square foot. The price of the Box beams were 56% higher than the estimated price and this was attributed to the high demand for Box beams during that particular time, besides the temporary shortage of cement. The increased cost of transportation was also a factor. The bid price of the precast abutments per cubic yard of concrete was 80% higher than conventional cast in place concrete.

CONCLUSION

Overall, the precast systems were fabricated as designed and erected efficiently as expected. The contractors were very pleased with the swiftness with which they could handle the precast units and also the ease of installation. At final inspection and finalizing submittals, the contractor and Maine DOT gave each other high marks for job satisfaction. This was truly a project which had many challenges but finally came together with the help of dedicated teams from both the Maine DOT and the contractors, and certainly with the technology of precast units. The success of this project and that of the Andover PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE

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Dam Bridge has motivated other designers at Maine DOT to consider similar All-Precast solution on their projects.



Figure 1: Precast Abutment Section showing void and PT bar locations.


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Figure 2: Precast Abutment dimensions.



Figure 3: Embankment details showing new and existing abutment.

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Figure 4: Typical Superstructure Cross-Section.



Figure 5: Typical Abutment Elevation.

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Photo 1: Removal of Existing Steel Girder Bridge.

Photo 2: Extensive use of Geotextiles to stabilize Causeway.



Photo 3: Placement of Center Precast Abutment units.

Photo 4: Precast Abutment voids being aligned with Pile tips.

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Photo 5: Self-Consolidating Concrete poured into the voids.

Photo 6: All four Precast Abutment units in place



Photo 7: Launching Beam and first Precast Box beam in place.

Photo 8: Completed Bridge showing causeways.

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Photo 9: Completed Bridge photo taken 9 months after completion.



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SECTION 10: CASE STUDY 3, MILL STREET BRIDGE, EPPING, NEW HAMPSHIRE Article Download: http://www.pci.org/pdf/publications/journal/2005/may-june/jl-05-may-june-4.pdf

CASE STUDY 3 Mill Street Bridge Epping, New Hampshire PCI Journal Article JR-449

GUIDELINES R-2

FOR ACCELERATED BRIDGE CONSTRUCTION USING PRECAST/PRESTRESSED CONCRETE COMPONENTS

References and Resources AASHTO LRFD Bridge Design Specifications, 3rd Edition with 2006 Interim Revisions, American Association of State Highway and Transportation Officials. AASHTO Standard Specifications for Highway Bridges, 17th Edition, American Association of State Highway and Transportation Officials. PCI, Manual for Quality Control for Plants and Production of Precast and Prestressed Concrete Products PCI MNL-116. Precast/Prestressed Concrete Institute, Chicago, IL. PCI. 2000. Tolerance Manual for Precast and Prestressed Concrete Construction, First Edition, MNL 135-00. Precast/Prestressed Concrete Institute, Chicago, IL. PCI. 1997. Bridge Design Manual PCI MNL-133-97. Precast/Prestressed Concrete Institute, Chicago, IL. ACI, 2001. Emulating Cast-in-Place Detailing in Precast Concrete Structure ACI 550.1R-01, American Concrete Institute, Farmington Hills, MI ASBI, Construction Practice Handbook For Segmental Concrete Bridges, American Segmental Bridge Institute FHWA, Decision-Making Framework for Prefabricated Bridge Elements and Systems (PBES), May 2006, Federal Highway Administration, Washington, D.C. Design Guidelines (available at www.pcine.org) New England Bulb Tee (NEBT) Post-Tensioned Design Guidelines (June 2001) This report covers design, detailing and construction specifications for post-tensioning and splicing of the New England Bulb Tee (NEBT) girder. Splicing of the girders allows for longer span lengths and the elimination of intermediate bridge piers. Post-tensioning can be used to make bridges continuous. If a State standard exists it will take precedence over these guidelines & details. Load Charts for New England Bulb Tee - LRFD Load Charts (1998) Preliminary Design charts for designing the New England Bulb Tee Girders. Charts will help you determine span capabilities, spacing and preliminary number of prestressing strands required. If a State Standard exists it will take precedence over these guidelines and details. Load Charts for New England Bulb Tee - HS25 Load Charts (1998) Preliminary Design charts for designing the New England Bulb Tee Girders. Charts will help you determine span capabilities, spacing and preliminary number of prestressing strands required. If a State Standard exists it will take precedence over these guidelines and details. Load Charts for New England Bulb Tee - HS20 Load Charts (1998) Preliminary Design charts for designing the New England Bulb Tee Girders. Charts will help you determine span capabilities, spacing and preliminary number of prestressing strands required. If a State Standard exists it will take precedence over these guidelines and details. Load Charts for New England Bulb Tee - Instructions for Use and Section Properties (1998) Preliminary Design charts for designing the New England Bulb Tee Girders. Charts will help you determine span capabilities, spacing and preliminary number of prestressing strands required. If a State Standard exists it will take precedence over these guidelines and details. PCI – NORTHEAST TECHNICAL BRIDGE COMMITTEE


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Full Depth Precast Concrete Deck Slabs (June 2002) Design Guidelines for the use of Full Depth Precast Deck Slabs used for new construction or for replacement of existing decks on bridges. This guideline has been reviewed and approved by the New England Technical committee. Several projects have already used these details and specification. If a State Standard exists it will take precedence. High Performance Concrete for Prestressed Concrete Bridges (September 2001) Guide specification for High Performance Concrete developed by New Hampshire DOT. New Hampshire is the lead state under the Federal Highway demonstration project for HPC in our region. This guideline has been reviewed and approved by the New England Technical committee. Several projects have already used this specification. If a State Standard exists it will take precedence. Bridge Member Repair Guidelines (January 2003) This report is intended to serve as a guide to identify defects that may occur during the fabrication of bridge elements. The report gives guidance on possible cause and prevention. It will help determine the consequences of the defects and assist in making a judgment as to acceptance/repair or rejection. This report can be utilized by State Inspectors, Designers, Plant Production Managers, Plant Quality Control Inspectors and Plant Engineers. Prestressed Concrete Girder Continuity Connection (May 1998) Guidelines for simple span members made continuous in Multi-span bridges. This specification and its sample details shall be used as a guide when designing for continuity. The PCI New England Technical committee has recommended that strand extensions be used to make the positive moment connection in beams. If a State Standard exists it will take precedence over these guidelines & details. Precast Deck Panel Guidelines (May 2001) Guidelines and details for Precast Prestressed Concrete Deck Panels or Stay-in-Place (SIP) decking used as a permanent form spanning between girders and designed to act composite with the remaining cast-in-place deck. If a State Standard exists it will take precedence over these guidelines & details. Web Sites AASHTO Website bridges.transportation.org PCI National Website www.pci.org PCI-NE Website www.pcine.org, Belmont, MA FHWA Accelerated Bridge Construction Website: www.fhwa.dot.gov/bridge/accelerated, New Brunswick, New Jersey


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INDEX Anchoring Details Anchoring Bolts ............................................... 4-7 Bearing Assemblies.......................................... 4-8 Devices............................................................. 4-7 Elastomeric Bearing Pad .................................. 4-7 For Deck Components...................................... 4-8 Raised Pedestal................................................. 4-7 Steel Rail System ............................................. 4-8 Assembly Plan....................................... 5-1, 7-1, 7-2 Beam Type Box Beam......................................................... 1-5 Deck Slab ......................................................... 1-5 Voided Slab...................................................... 1-6 Component Abutment.......2-1, 2-2, 4-1, 4-5, 4-5, 4-8, 5-1, 5-4 Assembly..................... 2-1, 5-1, 5-3, 7-1, 7-2, 7-3 Backwalls ......................................................... 4-8 Battered ............................................................ 2-2 Cheek Walls ..................................................... 4-8 Installation............ 2-3, 3-1, 3-2, 3-2, 3-3, 7-2, 7-3 Keeper Block.................................................... 4-8 Pier Caps .......................................................... 4-3 Precast Concrete Rail ....................................... 4-7 Recessed Key ................................................... 5-1 Retaining Wall ............ 4-1, 4-3, 4-8, 5-1, 5-3, 7-3 Shape ................................................................ 2-2 Size......................................2-2, 4-5, 5-4, 5-5, 7-1 Spread Footing 3-1, 3-2, 3-2, 3-3, 3-4, 4-1, 4-4, 51 Spread Footings................................. 3-4, 4-5, 4-8 Stems .........................................................2-2, 4-3 Substructure..2-1, 2-2, 3-1, 3-3, 4-8, 7-1, 7-2, 7-4, 7-5 Wingwall .................................... 2-1, 2-2, 4-1, 4-8 Concrete Placement Cast-in-Place ...................1-5, 2-1, 3-2, 4-2, 5-1, 1 Precast ......................1-6, 2-1, 2-2, 3-3, 4-2, 7-3, 1 Conflicts ............................................................... 4-7 Connections.......2-1, 4-1, 4-3, 4-5, 4-7, 5-1, 5-3, 5-4 Construction ................................... 2-2, 3-1, 7-1, 7-3 Accelerated................................................3-1, 7-2 Concerns........................................................... 4-8 Conventional .................................................... 4-8 Costs................................................................. 1-1 Joints ................................................................ 2-1 Sequencing ....................................................... 4-1 Specification..................................................... 4-5 Speed .........................................................1-6, 4-2

Staged............................................................... 4-1 Substructure ............................... 3-1, 3-2, 3-2, 3-3 Tolerance............................. 4-5, 4-8, 5-5, 7-3, 7-4 Contractor ................ 3-1, 3-4, 4-1, 5-1, 7-1, 7-2, 7-4 Corrosion Protection .....................................2-3, 5-1 Costs Increases........................................................... 2-1 Design Assumptions..................................................... 2-1 Emulation......................................................... 2-1 Detours................................................................. 1-1 elastomeric bearing pad Elastomeric Bearing Pad.................................. 4-7 Environmental Impacts ........................................ 1-1 Fabrication .............................. 2-1, 2-2, 4-8, 7-3, 7-4 Tolerance.......................................................... 7-3 Field Drilling........................................................ 4-7 Fill Flowable....................................................7-4, 7-5 Geometry Battered ............................................................ 2-2 Footing Widths................................................. 2-2 Layout ........................................ 2-1, 4-1, 4-2, 7-3 Repetition..................................................2-1, 2-2 Skew................................................................. 2-1 Tolerance.................................... 3-1, 5-3, 5-5, 7-3 Grout Availability ...................................................... 7-3 Cable Grout...................................................... 7-3 Flowable....................................................5-1, 5-3 Footing ............................................................. 3-4 Installation.................................. 3-2, 5-1, 5-2, 5-4 Instruction ........................................................ 7-3 Joint...........................................................5-1, 5-3 Key................................................................... 5-2 Keys ..........................................................4-3, 4-4 Operation.................................... 3-4, 5-3, 5-4, 7-4 Post-Tensioning Ducts ..............................5-4, 5-5 Prepackaged ..................................................... 5-1 Preparation ....................................................... 7-4 Pressure ............................................................ 5-3 Pumping .............................. 3-4, 5-1, 5-2, 5-4, 5-4 Sealing.............................................................. 4-8 Shear Key..................................................4-3, 4-4 Sleeve........................................................4-2, 5-4 Specifications ................................................... 7-2 Spicer ............................................................... 5-3 Splicer .............................................................. 5-2

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Strength .....................................................3-4, 5-1 Structural .......................................................... 5-3 Type ..........................................................5-1, 5-3 Under Footing ...........................................3-1, 3-2 Handling............................................................... 2-2 Integral Abutment ................................................ 4-3 Joints Construction ..................................................... 2-1 Contraction....................................................... 4-8 Expansion......................................................... 4-8 Filler Installation .............................................. 5-3 Non-Structural Joints ....................................... 4-8 Sealing.............................................................. 4-8


Lateral forces ....................................................... 4-8 Movement ............................................................ 4-8 Overturning Loads ............................................... 5-1 Political Pressures ................................................ 1-1 Post-tensioning..................................................... 2-1 Precast Plant......................................................... 4-7 Rapid Bridge Construction............................1-1, 1-6 Settlement ............................................................ 4-8 Shear Capacity ..................................................... 5-1 Shipping ............................................................... 2-2 Equipment ............ 2-2, 3-4, 5-4, 7-1, 7-2, 7-2, 7-4 Temporary Facilities ............................................ 1-1 Transportation ...................................................... 2-2


NOTES

NOTES

NOTES

116 Radcliffe Road, Belmont, MA 02478 Phone (888) 700-5670 http://www.pcine.org

Acelerated Precast Bridges PCI

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