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Performance Estimates in Seismically Isolated Bridge Structures

Performance Estimates in Seismically Isolated Bridge Structures. Gordon Warn Young Researchers’ Symposium Tokyo, Japan June 2003. Personal information. Graduate research assistant Department of Civil, Structural, and Environmental Engineering Primary research interests

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Performance Estimates in Seismically Isolated Bridge Structures

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  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

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