Integrating Durability and Structural Design

Integrating Durability and Structural Design

By Buckland and Taylor  COWI 1

MARCH 2014 BRIDGE SERVICE LIFE

Agenda 1. Introduction 2. FIB Bulletin 34 Model Code for Service Life Design 3. Recent B&T Projects in the U.S.A: ›

Tappan Zee Hudson River Crossing

›

Ohio River Bridges: Downtown Crossing

›

St.Croix Crossing (preliminary study)

4. Added value

2


Introduction › Structural concrete: › a universal building material › a universal building problem?

› Life-Cycle Cost Analysis & Corrosion Protection Plan › New major structures are designed for 100+ year service life

Bridge girder - Canada

3


Service Life Challenges for Texas Infrastructures › Extremely severe environment + materials prone to deterioration › Chloride-induced corrosion › Documented cases of alkali-aggregate reactions › Documented cases of delayed ettringite formation

› Premature degradation leads to: › Increase of maintenance and rehabilitation costs › Loss of serviceability for users, negative impacts on the community Parapets - California

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How is service life considered? › Structural design standards do not specifically account for service life › AASHTO LRFD Bridge Design Specifications › ACI 318 Building Code Requirements for Structural Concrete

› Codes and standards as design basis: › Assumed life is typically 75 years › Lack models for predicting deterioration › No metric to verify if a durable design is achieved

› Knowledge base is 10-30+ years › "Deemed to satisfy rules"

5


Bridge girder - Canada

FIB Bulletin 34 Model Code for Service Life Design › ISO 16204:2012 Service Life Design of Concrete Structures › Developed by the International Federation for Structural Concrete (fib) › Open-source methodology

› Used and validated internationally

› A reliability-based service life design methodology for concrete structure › Provides a proven, objective means of establishing service life design › Contrasts with the historical empirical approach that has resulted in the customary prescriptive specifications › Simple concrete testing that provides means to verify the durability requirements are achieved

Implemented on 3 major American projects in New York, Kentucky, and Minnesota 6


Terms of definitions Other administrative provisions

FIB Bulletin 34 Model Code for Service Life Design Principles of service life

A

Full probabilistic approach

B

Avoidance of deterioration

Probabilistic models: - Resistances - Load/exposure - Geometry

Exposure classes

Limit states

Design provisions

Design/verifications Project specification for material selection and execution Maintenance plan Inspection/monitoring plan 7


Quality plan for execution (optional)

n case of non-conformity with the performance criteria, the tructure becomes either obsolete or subject to a redesign

Design criteria Deemed to satisfy

FIB Bulletin 34 Model Code for Service Life Design

Strategy A Full probabilistic methodology

Strategy B Avoidance of deterioration / Deemed to satisfy

Chloride-induced corrosion

Alkali-aggregate reaction

Carbonation-induced corrosion

Freeze-thaw degradation Salt weathering Delayed ettringite formation Sulfate attack

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FIB Bulletin 34 Model Code for Service Life Design 1. Select limit state ›

Service life = Years until major maintenance = Years until corrosion initiation

›

10% probability of exceedence

2. Define exposure zones and degradation mechanisms › STRATEGY A: PROBABILISTIC ANALYSIS › Modeling of chloride ingress and carbonation based on Fick's Laws of diffusion › Quantification of probabilistic variables

› STRATEGY B: AVOIDANCE OF DETERIORATION

3. Design Parameters › Materials › Concrete quality › Concrete cover

4. Project Specifications 9


5. Construction  pre-testing and production testing

Define exposure zones and degradation mechanisms

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Design Parameters

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Mix 1

Mix 2

Mix 3

Construction - Durability Testing › Concrete testing to verify requirements are met: › trial phase › construction phase

› fib Model Code is based on the NT Build 492: Rapid Chloride Migration Test › perform at 28 days of concrete age › duration: 1 day › direct input parameter in model

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How does this concrete durability study affect the structural design? › Requirements for concrete cover › Type of reinforcing steel

Concrete Cover

› Quantifiable requirements for the concrete quality

Concrete Quality 13


Tappan Zee Hudson River Crossing › Project description › total length of 4881 m (16 013 ft.) › main span length of 369 m (1 200 ft.)

› B&T's role: › Structural design for the main span bridge › Corrosion Protection Plan for the main span bridge and approach span bridges › Operations and maintenance planning › Structural health monitoring system design › Ship impact assessment

› Project requirements: › 100-year service life for non-replaceable components 14


Ohio River Bridges Downtown Crossing › Project description › Interstate 65 corridor Kentucky-Indiana › total length of 2106 feet › cable stayed structure

› Role of B&T: › Structural design for the main span bridge › Corrosion Protection Plan for the main span bridge

› Project requirements: › 100-year service life for non-replaceable components

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St.Croix Crossing › Project description › Interstate 36 corridor MinnesotaWisconsin › total length of 3360 feet › extradosed bridge

› Role of B&T: › Structural design for the main span bridge › Independent check of approach bridges › Preliminary durability analysis for the main span pylons

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Opportunities to Provide Solutions to Bridge Owners › Reduce life-cycle costs by achieving a 100+ year service life › Use a scientific and documented methodology for service life design › ISO 16204:2012 Service Life Design of Concrete Structures (FIB Bulletin 34) › Implemented on 3 major American projects

› Integration of structural design with service life design › B&T structural engineers work in collaboration with durability specialists to provide adequate structural detailing

› Definition of durability metrics is a win-win situation for all parties involved on the project › Contractor can demonstrates how service life requirements are met › Owner can be confident that service life requirements will be achieved 17


Bridge Substructure Canada

Thank You.

18


Integrating Durability and Structural Design

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