Performance Estimates in Seismically Isolated Bridge Structures

1. Performance Estimates in Seismically Isolated Bridge Structures Gordon Warn Young Researchers’ Symposium Tokyo, Japan June 2003

2. Personal information • Graduate research assistant • Department of Civil, Structural, and Environmental Engineering • Primary research interests • Seismic Isolation, Passive Energy Dissipation Systems, Bridge Engineering • Academic advisor: Professor Andrew Whittaker

3. Technical approach • Perform numerical simulation • Simple bridge model • Varied isolator parameters • Performance measures • Maximum isolator displacement • Review accuracy of static analysis procedure • Determine increase in displacement due to bidirectional seismic excitation • Energy demands • Develop prototype testing protocol

4. Seismic isolation systems

5. Seismic isolation hardware

6. Performance measures • Displacement estimate influences all aspects of analysis, design and construction • Superstructure and substructure forces • Design and full-scale testing of seismic isolators • Stability and strain demands for elastomeric bearings • Plan dimensions of sliding systems • Energy demand on seismic isolators • Design and full-scale testing of seismic isolators • Bearing acceptance criteria

7. Modeling seismic isolators • Lead-Rubber (LR) bearings • Coupled plasticity model • Bouc-Wen model • Friction Pendulum (FP) bearings • Coupled plasticity model • Account for variations in axial load • Bouc-Wen model

8. Effect of bidirectional shaking

9. Displacement estimates • Displacement estimate • Based upon work in the 1980s • Constant velocity region of the spectrum • Unidirectional response • Results of nonlinear response analysis • Benchmarked to static equation (buildings)

10. Displacement estimates • Bin description adapted from that developed by Krawinkler • Magnitude and distance-to-fault based on mainshock • Ground motions extracted from the PEER and SAC databases

11. Displacement estimates • Spectral demands for NF (Bin 1) • 5% critical damping

12. Force Kd Qd Displ. dmax Displacement estimates • Response-history analysis • Unidirectional (URHA) • Bidirectional (BRHA) • Simple isolated bridge model • Rigid super- and substructures • Bilinear isolation systems considered

13. Displacement estimates • Bidirectional excitation • Unidirectional excitation

14. Displacement estimates • Update displacement equation • Option a: • Unidirectional displacement multiplier: • Based on results of URHA and BRHA • Orthogonal component • Coupled behavior of LR and FP bearings

15. Displacement estimates • Displacement multiplier Bin 2M: LMSD

16. Energy dissipation demands • Interpretation of isolator performance • AASHTO (Seismic Test) • 3 fully reversed cycles at 0.25dt,....1.25dt • 10 to 25 fully reversed cycles at 1.0d • 3 fully reversed cycles at dt

17. Force Fmax Fy Kd Qd Ku Displ. dmax dyield EDC Energy dissipated demands Normalized Energy Dissipated (NED )

18. NED for NF ground motions Bidirectional response-history analysis

19. Normalized energy dissipated Td =2.0 seconds

20. Energy dissipated demands Rate-of-energy dissipated Isolator properties: Qd=0.06 Td =4.0 sec. Ground motion component: RIO360

21. Force Keff Kd Qd Displ. dmax Energy dissipated demands Equivalent harmonic frequency Results of URHA using ground motion record: RIO360

22. Conclusions • Update displacement equation • Orthogonal component • Coupled behavior • Preliminary estimates of suggest 1.5-1.75 • AASHTO testing protocols • Overly demanding (NED ) • Performed statically (no specified frequency) • Replace with: 4 fully reversed cycles at T

23. Acknowledgements • Professor Andrew Whittaker • Professor Kawashima • MCEER / FHWA • Natural Hazard Mitigation in Japan Program • National Science Foundation • Japan Society for the Promotion of Science