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Advancing NGA-West2 Project: Enhancing Site Response Models for Safer Infrastructure

This project aims to improve site response models for infrastructure safety. Experts review NEHRP factors and NGA-West terms, focusing on evaluating site factors for seismic activity. Methods include simulation-driven evaluation and empirical analysis. Key discussions and comparisons are made towards achieving consensus on site factor revisions. The project explores various approaches and input parameters to enhance understanding and prediction of site effects. Collaboration among technical experts ensures the project meets its objectives and deliverables.

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Advancing NGA-West2 Project: Enhancing Site Response Models for Safer Infrastructure

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  1. Further Development of Site Response in NGA Models PEER Lifelines Program NGA-West2 Project Topic #8 Working Group Meeting Kickoff Meeting April 20, 2010

  2. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  3. Project Management • Yousef Bozorgnia, PEER, NGA-West2 Project Manager • Jonathan P. Stewart, UC Los Angeles (Working Group Chair) • Emel Seyhan, UC Los Angeles (GSR)

  4. Working Group Committee (WGC) • Don Anderson, CH2MHill, Bellevue, WA (Geotechnical engineer, TS3 Member) • Roger Borcherdt, USGS, Menlo Park, CA (Engineering seismology, developer of NEHRP site factors) • C. B. Crouse, URS Corporation, Seattle, WA (Geotechnical engineer, TS3 Chair and PUC Member) • R.W. Graves, URS, Pasadena, CA (Seismologist, ground motion simulation and basin effects) • I.M. Idriss, UC Davis, Santa Fe, NM (Geotechnical engineer, GMPE developer) • Maury Power, AMEC Geomatrix, Oakland, CA (Geotechnical engineer, for TS3 Chair) • Walter Silva, PEA, El Cerrito, CA (Seismologist, NGA database manager, GMPE developer) • Thomas Shantz, Caltrans, Sacrament, CA (Geotechnical engineer)

  5. Working Group Committee (WGC) • Do we need others?

  6. Logistics • Database provided by NGA-West2 (PEA) • Technical work by UCLA researchers • Oversight of work direction/results by WGC • Oversight of WGC by …? • Deliverables: • Check of NGA-W models (trends with Vs30, nonlinearity, sigma) • Evaluate basin depth effects • Develop technical basis for, and consensus behind, revisions to NEHRP site factors

  7. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  8. NGA-West2 Overview and Project Objectives Yousef Bozorgnia

  9. Background on NEHRP Site Factors Roger Borcherdt

  10. Results from Previous NGA Site Factor Working Group Maury Power

  11. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  12. Outline • Evaluation of Site Factors • Available approaches • Approaches adopted in NEHRP and NGA GMPEs • Input parameters • Comparison of NGA & NEHRP site terms

  13. G/GMax D g Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D Output V s Rock Att. Input

  14. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D Day et al. 2008

  15. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) Walling et al. 2008

  16. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) Walling et al. 2008

  17. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Walling et al. 2008

  18. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Day et al. 2008

  19. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Day et al. 2008

  20. Evaluation of Site Factors • Simulation driven: • Not used as “stand alone” factors for active regions • Used to constrain certain aspects of “hybrid” models

  21. Evaluation of Site Factors • Simulation driven • Empirical (reference site approach) • Single event • IMsoil/IMref: evaluate dependence on site condition and PGAref Borcherdt 2002

  22. Evaluation of Site Factors • Simulation driven • Empirical (reference site approach) • Empirical (non-reference site approach) • Multiple events • Analysis of residuals • Evaluate dependence on site condition, PGArock, etc. Choi & Stewart 2005

  23. Evaluation of Site Factors Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  24. Evaluation of Site Factors NEHRP Factors Nonlinearity Weak Motion Amplification Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  25. Evaluation of Site Factors NGA: AS, CB Amplification level; Vs30-dependence Nonlinearity Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  26. Evaluation of Site Factors NGA: BA, CY Nonlinearity; Amplification level; Vs30-dependence Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  27. Evaluation of Site Factors • Input parameters: • NEHRP: Vs30, Ss, S1 • AS: VS30, Median PGA1100 • BA: VS30, Median PGA760 • CB: VS30, Median PGA1100 • CY: VS30, Median + i (Sa)1130

  28. 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=150, 270, 560, 760, and 1100 m/s • Evaluate F at T=0.3 and 1.0 sec.

  29. NGA-NEHRP Comparisons • Ax: • A=median PGA for AS, BA, CB • A=Sa at period of interest for CY (median + i); Take Sa(0.3)=2.5×PGA and Sa(1.0)=1.0×PGA • Adopt reference condition of 760 m/s • F760(Vs30, Ax)=Fx(Vs30, Ax)-Fx(760, Ax)

  30. D C B B NEHRP E

  31. Suggestions on NEHRP-NGA comparisons • Average Sa across all NGA periods in the ranges for Fa and Fv. Use average of logs + limits. Exact middle of the range too (e.g. 0.3 sec for Fa, 1.2 sec for Fv) • Average across velocities in site class: use wt average based on histograms of Vs30. • Ask Brian how he plotted F vs PGA • Check coding using full models. • Check NGA errata for AS

  32. Residuals Analysis • WS: run NGA for 760 with NEHRP factors and look at residuals. • All sites and estimates Vs only • Use GMRotI50 • New data: • Use June 2010 version of NGA flat file • Alan Yong, USGS: he has funding to perform site investigations. His site list has been approved, previous efforts to provide input on sites to investigate have been resisted

  33. Residuals Analysis • New data: • Residuals analysis, including Baja earthquake data, focusing on low Vs30 range.

  34. Other recommendations • USGS maps for all Vs30s, with interpolation (next generation of mapping) • When we have the new factors, compare hybrid predictions with them & old factors with full psha for various sites in Nor Cal and So Cal. • Check sites without Vs using Virtual Geotechnical Data Center (TS will send url and password). • Google earth file with CA stations, see where E stations are (look at other categories too).

  35. NGA-NEHRP Comparisons Differences: • NEHRP Fv high • Esp for C to E • NEHRP nonlinearity stronger for C to D • NEHRP Fa and Fv high for rock (Class B)

  36. Working Group Objectives & Scope

  37. Objectives • Input to NGA-West2 developers • Develop technical basis for, and consensus behind, revisions to NEHRP site factors • Problems with medians • Different sigmas

  38. Task Order Scope • Database

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