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Further Development of Site Response in NGA Models

Further Development of Site Response in NGA Models. PEER Lifelines Program NGA-West2 Project Topic #8 Working Group Meeting. Meeting #2. October 26, 2010. Agenda. Review project objectives and status (Stewart) Status of NGA-W2 database (Bozorgnia, Silva)

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Further Development of Site Response in NGA Models

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  1. Further Development of Site Response in NGA Models PEER Lifelines Program NGA-West2 Project Topic #8 Working Group Meeting Meeting #2 October 26, 2010

  2. Agenda • Review project objectives and status (Stewart) • Status of NGA-W2 database (Bozorgnia, Silva) • Update on comparison of NEHRP and NGA site factors (Seyhan) • Project scope (Stewart and group) • Scope as presented in proposal • Open discussion of research priorities • Sub-contract procedures (Seyhan)

  3. Project Objectives and Status • NEHRP site factors • Wk motion: empirical AFs, reference site approach • Nonlinearity from simulations • NGA site factors • Empirical AFs, non-reference site approach • Simulations • NEHRP and NGA site factors inconsistent

  4. Project Objectives and Status • “The principal objective of this project is to identify and better understand those discrepancies for the IMs of interest in the NGA-West2 project and propose new site factors for application in NEHRP that will resolve the differences.”

  5. Project Objectives and Status • “Additional, related objectives concern enhancing the site database developed in the original NGA project to incorporate the results of additional site characterization efforts, and to check the performance of the existing NGA site factors through analyses of residuals. Those residuals analysis efforts will emphasize, but not be limited to, data collected since the original NGA project (approximately 1500 recordings) .”

  6. Status of NGA W2 Database Yousef Bozorgnia Walt Silva

  7. Emel Seyhan University of California, Los Angeles Comparison of NEHRP Site Amplification Factors and the NGA Relationships

  8. Outline Introduction Analysis Procedure • Data Used for Site Classifications • Amplification within Vs30 Categories • Variation of Amplification with Vs30 Conclusions

  9. NGA-NEHRP Comparisons In natural log units, site term = Fx(Vs30, Ax) • Fx=amplification relative to Vs30=x site condition • Ax=ground motion amplitude for reference site condition of Vs30=x Use Vs30=157, 275, 425, 760, and 1047 m/s Evaluate F at T=0.3 and 1.2 sec.

  10. Input Parameters • AS: VS30, Median PGA1100 • BA: VS30, Median PGA760 • CB: VS30, Median PGA1100 • Take A = PGA • CY: VS30, Median + i (Sa)1130 • Take A= Sa(0.3)=2.2*PGAr and Sa(1.0)=1.0*PGAr Adopt reference condition of 760 m/s F760(Vs30, Ax)=Fx(Vs30, Ax)-Fx(760, Ax)

  11. Histogramof Vs30 for Strong Motion Sites

  12. Class C and D

  13. Short - Period T=0.1, 0.3, 0.5 sec * Vs30=1074 m/s is typo. It is 1047 m/s.

  14. Short - Period T=0.1, 0.3, 0.5 sec * Vs30=1074 m/s is typo. It is 1047 m/s.

  15. Mid - Period T=0.4, 1.2, 2.0 sec * Vs30=1074 m/s is typo. It is 1047 m/s.

  16. Mid - Period T=0.4, 1.2, 2.0 sec * Vs30=1074 m/s is typo. It is 1047 m/s.

  17. Averaged across corresponding period ranges • 0.1-0.5 sec for Fa; • 0.4-2.0 sec for Fv • Used Vs30 values • 275 and 425 m/s

  18. Variation of Amplification with Vs30 Differences: • NEHRP Fv high • esp. Class C to E • NEHRP nonlinearity stronger • Class C to D • NEHRP Fa and Fv high for rock • Class B

  19. Concluding Remarks Amplification at short and long period ranges exhibit a decreasing trend with increasing velocities Nonlinearity of amplification factors vary with Vs30, especially for Vs30<180 m/s and relatively small for Vs30~275 m/s. For amplification variation with Vs30 NEHRP mid period Fv are high, especially for Class C to E. Bias in weak motion amplification for Fv NEHRP nonlinearity stronger for Class C to D. NEHRP Fa and Fv high for rock associated with Class B.

  20. Project Scope • Task 1: Direct site factors comparison – complete? • Task 2: Database development • Main NGA-W2 database from PEA • Review and possibly add additional parameters & data • Possible use of virtual geotechnical data center (?)

  21. Project Scope • Task 3: Data analysis • Non-Reference Site Approach • Residuals analysis (new and original NGA data) relative to median for Vs30=760 m/s. • Check against basin depth and other parameters (e.g., f0, etc.) • Look at standard deviations • Residuals for motions computed with NEHRP factors • Reference Site Approach • Identify soil/rock pairs (need to develop criteria for selection) • Use GIS database to help in identifying station pairs? • Compare to site factors from non-reference site approach • Emphasize soft soil sites in above work

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