ACI Committee 341-C State-of-the-Art Summary Seismic Evaluation and Retrofit Techniques for Concrete Bridges

Committee 341-C Retrofit of Concrete Bridges Sub-committee members: –Dawn Lehman and Sri Sritharan (co-chairs) –Adolfo Matamoros, Anthony Powers, David Sander (authors) –Ayman Salama, Raj Valluvan, Eric Williamson Additional Contributions: –Photographs: NISEE Image DatabaseImage Database –Analysis of SR-99: WashDOT UW: Blake Inouye, John Stanton, Dawn Lehman

1971 San Fernando Bridge Damage in Previous Earthquakes

1989 Loma Prieta Bridge Damage in Previous Earthquakes

1994 Northridge Bridge Damage in Previous Earthquakes

1995 Kobe Bridge Damage in Previous Earthquakes

Report Objectives Describe key aspects of seismic retrofit program –General understanding of each phase –Conceptual design and analysis methods Emphasize design for structural stability Rich resource of appropriate references

Resource Evaluation Multi-Phase Program IMPLEMENTATION Member Response Global Response SELECTION AND DESIGN OF RETROFIT MEASURES SEISMIC EVALUATION OF EXISTING SYSTEM System Capacity Seismic Demand Demand/Capacity Ratio Phases of Retrofit Program SEISMIC VULNERABILITY EVALUATION Seismic Hazard Structural Vulnerabilities Socio-Economic Consequences

Phases of Retrofit Program: Seismic Vulnerability Evaluation Local Soil Conditions Soil Response and Failure Source Path Site Evaluation of Site-Specific Hazard

Phases of Retrofit Program: Seismic Vulnerability Evaluation Geometry Date of Design and Construction Evaluation of Structural Vulnerability

Phases of Retrofit Program: Seismic Vulnerability Evaluation Evaluation of Socio-Economic Consequences Casualties Lifeline Interruption Economic Impact

Phases of Retrofit Program: Seismic Demand/Capacity Evaluation Determine as-built conditions Existing material properties Estimate capacity of components Evaluation of Seismic Capacity (Priestley et al., 1994)

Phases of Retrofit Program: Seismic Demand/Capacity Evaluation Established Analysis Methods Linear or Nonlinear Multi-Spectra or Time-History Evaluation of Seismic Demand

Phases of Retrofit Program: Seismic Demand/Capacity Evaluation  Determine Demand/Capacity Ratios Global Displacement Local Deformations and Forces

Phases of Retrofit Program: Seismic Retrofit Measures Based on Demand/Capacity Evaluation Select at Member and/or System Level Address Global Response

Phases of Retrofit Program: Implementation Multi-Phase Retrofit Programs Depends on State and DOT Initial Retrofit Measures Cable Restrainer More Costly Measures: Beam and Column Retrofit

Sri Sritharan Tony Powers SELECTION AND DESIGN OF RETROFIT MEASURES SEISMIC EVALUATION OF EXISTING SYSTEM Adolfo Matamoros Presentation of Report SEISMIC VULNERABILITY EVALUATION David Sanders INTRODUCTION CONCLUSIONS EDITING Dawn Lehman

Seismic Vulnerability Evaluation Bridge Geometry Structural Redundancy Expansion Joints Age of Design ~ Vulnerable Elements Structural Condition Condition of Supporting Soil

Seismic Vulnerability Evaluation Bridge Geometry Bent Configurations Degree of Skew or Curvature Flared Columns Short Seat Widths Multi-Level Systems Multiple Superstructure Types

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Inadequate Confinement Inadequate Shear Strength Location and Strength of Lap Splices

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Reduced Flexural Strength (Insufficient Bar Anchorage) Inadequate Shear Strength Inadequate Strength in Torsion

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Insufficient Bar Anchorage Inadequate Shear Strength Inadequate Joint Steel

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Insufficient Flexural Strength Inadequate Shear Strength Inadequate Anchorage

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Insufficient Seat Length Bearing Instability

Seismic Vulnerability Evaluation Vulnerable Elements Columns Cap Beams Joints Foundations Hinges and Supports Superstructure Abutments Lack of Transverse Shear Keys Damage from Skewed Bridges Settlement

Seismic Evaluation Seismic Demand Seismic Capacity Demand/Capacity Ratios

Seismic Evaluation: Seismic Demand Determine Appropriate Analysis Method –Linear –Nonlinear Develop Model Evaluate Demands for Design Earthquakes

Seismic Demand Evaluation: Appropriate Analysis Method Linear –Single-Mode Response Spectrum “Simple” System Regular Mass and Stiffness –Multi-Mode Response Spectra More Complex System Irregular Mass, Stiffness Geometry –Time History Complex System Soil Springs/Dampers

Seismic Demand Evaluation: Appropriate Analysis Method Nonlinear Analysis Methods –Limit or Pushover Analysis Demands on System (Target Displacement) Paired with a Dynamic Analysis –Stand Alone Frame Analysis Provides Information on Nonlinear Behavior Neglects Frame and Abutment Interaction –Time History Analysis

Example of: Appropriate Analysis Method SR-99 Bridge Partial Retrofit Different Superstructure Systems Retrofit Outrigger Joints and Beams?

Example of: Appropriate Analysis Method Time-History Analysis Gap Elements Soil Springs Abutment North + Off-ramp SteelSouth North Steel Off-ramp Abutment Steel & South Concrete Structures

Example of: Appropriate Analysis Method Modeling Issues –Material Strengths –Effective Stiffness Values –Stiffness of Jacketed Columns –Model of Superstructure –Stiffness of Adjacent Structures –Soil Springs and Dampers

Example of Appropriate Analysis Method: Model Verification Red Gaps = Closed Gap Closures Predicted: 72 yr. EQ Actual: Nisqually EQ

Example of: Appropriate Analysis Method Analysis Results: Drift Demands in Outrigger Joints ID Yielding Columns From Capacity Evaluation: Joint Shear Stress Demands Beam Torsion Demands Beam Shear Demands

Seismic Evaluation: Seismic Capacity Determine Expected Material Strengths –Overstrength in Concrete: Aging –Overstrength in Steel: Strain-Hardening, Material Calculate Element Capacities –Calculate Flexural Capacities –Calculate Shear Strength –Calculate Anchorage or Development Strength

Seismic Capacity/Demand Evaluation 1.Calculate D/C Ratios for All Elements 2.Determine Critical Failure Modes/Elements 3.Determine Appropriate Retrofit Measures

Example of: Demand/Capacity Evaluation Critical Elements –Beam in Torsion –Exterior Anchorage in Joint Retrofit Measure –Steel Jacketing Beams & Joints

Sri Sritharan Tony Powers SELECTION AND DESIGN OF RETROFIT MEASURES SEISMIC EVALUATION OF EXISTING SYSTEM Adolfo Matamoros Presentation of Report SEISMIC VULNERABILITY EVALUATION David Sanders