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

2. 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

3. 1971 San Fernando Bridge Damage in Previous Earthquakes

4. 1989 Loma Prieta Bridge Damage in Previous Earthquakes

5. 1994 Northridge Bridge Damage in Previous Earthquakes

6. 1995 Kobe Bridge Damage in Previous Earthquakes

7. 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

8. 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

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

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

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

12. 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)

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

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

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

16. 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

17. 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

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

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

20. 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

21. 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

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

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

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

25. 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

26. Seismic Evaluation Seismic Demand Seismic Capacity Demand/Capacity Ratios

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

28. 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

29. 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

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

31. 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

32. 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

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

34. 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

35. 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

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

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

38. 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

39. ACI Subcommittee 341–C STATE OF THE ART SUMMARY ON SEISMIC RETROFIT TECHNIQUES FOR CONCRETE BRIDGES

40. Retrofit design philosophy Avoid excessive damage to members and prevent structural collapse of the bridge

41. Objective Satisfy strength and displacement demands expected under the design-level earthquakes. –Ensure a desirable yield mechanism –Limit inelastic actions to preselected locations –Column ends are typically selected in bridges –Avoid non-ductile response modes (e.g., shear and bond failure; inelastic response of non-ductile members)

42. Procedure Provide sufficient ductility capacity to the potential plastic hinge regions in columns Strengthen other members using capacity design principles using the column overstrength moments. Add new elements Reduce seismic demands to avoid inelastic response in capacity-protected members

43. Procedure (Cont..) Complete retrofit design at member level Analyze the retrofitted structure to ensure adequate response of the system. If necessary, redesign retrofit measures or introduce a new retrofit scheme

44. Columns Cap Beams Joints Footings Hinges and Supports Superstructure Abutments Vulnerable Structural Elements Inadequate Confinement Inadequate Shear Strength Location and Strength of Lap Splices

45. Provide uniform pressure Steel, concrete and advanced composites Use wraps or jackets Required over 1.5 to 2 times the length of the plastic hinge region Circular or oval shaped sections Leave a gap between column and wrap Fill gap with grout or concrete Leave a gap between the column and joint Confinement retrofit

46. (Courtesy of University of California, San Diego) Confinement retrofit – Circular column (Courtesy of Jacobs Civil Inc.)

47. (Courtesy of University of California, San Diego) Rectangular column

48. (Courtesy of Jacobs Civil Inc.) US40/I64 Double deck seismic retrofit in St. Louis

49. Active prestressed wire wraps and welded wire fabric (Courtesy of Jacobs Civil Inc.) Prefabricated composite jacketing of column (Courtesy of University of Southern California)

50. Improved Confinement Detail Section with curvature ductility of 20 10% – 75% increase in the effective elastic stiffness The new column stiffness should be included in the system level analysis of the retrofitted bridge

51. Non-Prismatic Columns (Courtesy of University of Nevada, Reno) U-shaped GFRP straps FRP straps Half shell steel jackets

52. (Courtesy of University of Nevada, Reno) Flared Columns Retrofitted with U-shaped GFRP Straps

53. Construction at US 395/I 80 Interchange, Reno (Courtesy of University of Nevada, Reno) Retrofitted Bent Multi-Column Bents – Transverse Direction

54. Column Lap Splice Retrofit Control dilatation strains Provide sufficient confinement Confinement retrofit required for the inelastic response may be sufficient Rectangular sections are not effective –unless spliced bars are welded for continuity

55. Column Retrofit to improve shear capacity Estimate demands –assume full development of column hinge –Include material over-strength Most techniques used for confinement retrofit are appropriate Retrofit is typically required along the full column height

56. (Courtesy of FHWA) CFRP (Courtesy of University of California, San Diego) Steel Jacket

57. Vulnerable Structural Elements Columns Cap Beams Joints Footings Hinges and Supports Superstructure Abutments Reduced Flexural Strength (Insufficient Bar Anchorage) Inadequate Shear Strength Inadequate Strength in Torsion

58. Post-tensioning cap beam is an effective retrofit measure –may require an increase in dimensions –may require addition of end blocks –will improve joint performance –will enhance torsional resistance Concrete bolsters and new reinforcement Steel jacket retrofit FRP wraps Cap Beam Retrofit Measures

59. Cap Beam Retrofit – Prestressing (Courtesy of Jacobs Civil Inc.) (Courtesy of University of California, San Diego)

60. (Courtesy of University of California, Berkeley) Adding Concrete Bolster

61. Reducing Seismic Demand (Courtesy of University of California, San Diego)

62. Vulnerable Structural Elements Columns Cap Beams Joints Footings Hinges and Supports Superstructure Abutments Insufficient Bar Anchorage Inadequate Shear Strength Inadequate Joint Steel

63. External prestressing Complete replacement of the joint region –increase in dimensions –Increase in column bar embedment length –new joint shear reinforcement Jacketing of the joint using concrete, steel or composite materials Reduce demand using a link beam Joint Retrofit Measures

64. Joint Retrofit (Courtesy of University of Utah) (Courtesy of University of California, San Diego)

65. Complete Joint Replacement (Courtesy of University of California, San Diego)