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

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)

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

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.”

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).”

Status of NGA W2 Database Yousef Bozorgnia Walt Silva

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

Outline Introduction Analysis Procedure –Data Used for Site Classifications –Amplification within V s30 Categories –Variation of Amplification with V s30 Conclusions

NGA-NEHRP Comparisons In natural log units, site term = F x (V s30, A x ) –F x =amplification relative to V s30 =x site condition –A x =ground motion amplitude for reference site condition of V s30 =x Use V s30 =157, 275, 425, 760, and 1047 m/s Evaluate F at T=0.3 and 1.2 sec.

Input Parameters –AS: V S30, Median PGA 1100 –BA: V S30, Median PGA 760 –CB: V S30, Median PGA 1100 Take A = PGA –CY: V S30, Median +  i (S a ) 1130 Take A= S a (0.3)=2.2*PGAr and S a (1.0)=1.0*PGAr Adopt reference condition of 760 m/s F 760 (V s30, A x )=F x (V s30, A x )-F x (760, A x )

Histogram of V s30 for Strong Motion Sites

Class C and D

Short - Period T=0.1, 0.3, 0.5 sec * V s30 =1074 m/s is typo. It is 1047 m/s.

Short - Period T=0.1, 0.3, 0.5 sec * V s30 =1074 m/s is typo. It is 1047 m/s.

Mid - Period T=0.4, 1.2, 2.0 sec * V s30 =1074 m/s is typo. It is 1047 m/s.

Mid - Period T=0.4, 1.2, 2.0 sec * V s30 =1074 m/s is typo. It is 1047 m/s.

Averaged across corresponding period ranges – sec for Fa; – sec for Fv Used V s30 values –275 and 425 m/s

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 Variation of Amplification with Vs30

Concluding Remarks Amplification at short and long period ranges exhibit a decreasing trend with increasing velocities Nonlinearity of amplification factors vary with V s30, especially for V s30 <180 m/s and relatively small for V s30 ~275 m/s. For amplification variation with V s30 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.

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 (?)

Project Scope Task 3: Data analysis –Non-Reference Site Approach Residuals analysis (new and original NGA data) relative to median for V s30 =760 m/s. Check against basin depth and other parameters (e.g., f 0, 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