1. Quick-Release Field Experiments on Seismically Isolated Bridges Stuart S. Chen, Ph.D., P.E. Associate Professor, University at Buffalo (SUNY), Fulbright Senior Lecturer, ITU

2. Presentation Outline Comprehensive Study Overview Bridges Studied Loading and Instrumentation Apparatus Selected Results Anticipating Seismic Performance Summary, Conclusions, Recommendations Acknowledgements

3. Comprehensive Study!: Overview Two Similar Bridges, Before and After Seismic Retrofit with Isolation Bearings Field (System Quick-Release) and Laboratory (Component Reverse-Cyclic) Experiments Comparing Analytical vs. Experimental Dynamic Behavior Inferring Seismic Performance from Calibrated Models

4. Seismic Isolation Concept (Kelly, 2001)

5. Seismic Isolation Concept (cont’d) (Kelly, 2001)

6. Bridges’ Plan View

7. Bridges’ Elevation; Brg. Schedule

8. Bridge Cross Sections

9. Bridge Bearing Replacement (Abut.)

10. Bridge Bearing Replacement (Pier)

11. Installing Isolation Brgs at Abutments

12. Southbound Abutment Isolator Kelly, 2001

13. Southbound Pier Isolator

14. Northbound Expansion Bearing (non-seismic)

15. Northbound Bridge Bearings

16. Objectives Measure and assess in-situ dynamic behavior and performance of typical slab- on- girder bridge subjected to transverse quick-release loading (steel brgs vs. seismic isolation brgs vs. standard laminated elastomeric brgs) Quantify in-situ dynamic performance change attributable to bearing retrofits

17. Objectives, cont’d Quantify Winter-Weather Effects on In-Situ Performance of Isolation and Elastomeric Bearings Assess Relative Merits of Several Modeling Approaches (at varying levels of complexity) in predicting transverse transient dynamic behavior of straight skewed slab-on-girder bridge structures

18. Loading Scheme

19. Loading Scheme (cont’d)

24. (Under-Bridge) Loading Scheme!

25. Loading Scheme (cont’d)

26. Loading Scheme: The Importance of Genuinely Quick Release!

27. Loading Scheme: Mechanical Fuse

28. Loading Scheme: Mechanical Fuse in Place

29. Selected Instrumentation

30. Selected Instrumentation (cont’d)

35. Selected Results: Free Vib’n

36. Pre-Retrofit in Frequency Domain

37. 1 st 2 Pre-Retrofit Mode Shapes

38. SAP Model

39. DRAIN-2DX Model

40. 3 rd Pre- Retrofit Mode Shape

41. Seismic Isolation Concept: Recall! SaSa TT SdSd ξ +

42. Post- Retrofit Time- History at Abutment

43. Post-Retrofit SB (Linear: “Portion 2”)

44. Post-Retrofit SB cont’d (Linear: Portion 2)

45. Post-Retrofit NB (Linear: Portion 2)

46. Post-Retrofit NB cont’d (Linear: Portion 2)

47. Selected NB Post-Retrofit T-H’s

48. Post-Retrofit SB cont’d

49. Post-Retrofit SB (Nonlinear: Portion 1)

50. Time, Temperature, Setup Effects (SB)

51. Old Steel Bearings: Not So Bad After All!

52. C/D vs. PGA, Pre-Retrofitted

53. C/D vs. PGA, Post-Retrofitted

54. Summary, Conclusions, Recommendations Transverse Quick-Release Experiments are successfully executed using the deployed apparatus Replacement of the original steel bearings with seismic isolation bearings leads to substantial behavior changes (period shift, etc.) in the transverse direction, as predicted. However, –Due to reserve strength of columns and steel bearings, actual seismic resistance of the retrofitted southbound bridge is not greatly increased by its seismic isolation retrofit, and –The torsional behavior induced in the retrofitted northbound bridge nullifies the otherwise seismically beneficial effect of its standard (non-seismic) elastomeric bearing retrofit

55. Summary, Conclusions, and Recommendations (cont’d) Neither a 3D Model nor formal structural identification methods produce any significant advantages over 2D modeling as long as nonlinear behavior is incorporated into the model (DRAIN-2DX) Cold-weather effects in western NY are not sufficiently severe to have a significant influence on LRB seismic isolation behavior

56. Acknowledgements J. B. Mander, D. Wendichansky, G. Pekcan, D.-K. Kim, I.-S. Ahn, L. Zhang, P. Dreyer, etc. New York State Dept. of Transportation, Union Concrete and Construction Corp. U.S. D.O.T. / Federal Highway Administration funding through NCEER/MCEER at the University at Buffalo