Shear Wave Velocity: Seismic Site Classification

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Shear Wave Velocity: Seismic Site Classification

  1. 1. Shear Wave Velocity- and Geology-BasedShear Wave Velocity and Geology Based Seismic Site Classification of Port-au-Prince Brady R. Cox, Ph.D., P.E.Brady R. Cox, Ph.D., P.E. The University of Arkansas Department of Civil Engineering Geotechnical Earthquake Engineering for Seismic Design Workshop, Department of Civil Engineering Port-au-Prince, Haiti, November 18-19, 2010
  2. 2. Seismic Site Classification Required by Seismic Provisions in Building CodesRequired by Seismic Provisions in Building Codes IBC (2009) ASCE 7-05
  3. 3. IBC & ASCE Codes – Seismic Site Classification Vs N SuSite Class: A - F > 1 500 m/s> 1,500 m/s 760 – 1,500 m/s 360 – 760 m/s 180 360 /180 – 360 m/s < 180 m/s V i f d b it i di tl l t d t th ASCE 7-05 Vs is preferred because it is directly related to the shear stiffness of the soil deposit (G = Vs 2)
  4. 4. Vs Measurement Locations in Port-au-Prince MASW used to determine Vs profiles at 36 locations across Port-au-Prince in April, 2010 Vs (Vs30) values calculated from the Vs profiles at each test location Show testing pictures Show site locations in Google Earth with Vs values and associated Seismic Site Classification Sit Cl BSite Class B Site Class C Site Class D/ESite Class D/E
  5. 5. MASW Surveys in Port-au-Prince For Seismic Site Classification A - E
  6. 6. Demo Locations, Vs Profiles, Vs Values Shear Wave Velocity (m/s) 0 0 4003002001000 Shear Wave Velocity (m/s) 20 10 5 60 40 Depth(ft) 15 Depth(m) 80 25 20 100 30 Vs = Vs30 = 250 m/s 160012008004000 Shear Wave Velocity (ft/sec) Site Class D
  7. 7. Locations Relative to Geology
  8. 8. Vs – Geology Correlations Shear Wave Velocity (m/s)Shear Wave Velocity (m/s) 150010005000 Shear Wave Velocity (m/s) Median profile with +/- 1 sigma 0 150010005000 Shear Wave Velocity (m/s) TL# 8 TL# 9 TL#10 20 TL#10 TL# 11 TL# 13 TL# 15 TL# 17 TL# 32 40 epth(ft) Vs profile comparison for geologic unit Qpf 80 60 De 100 80 6000400020000 Shear Wave Velocity (ft/sec) 6000400020000 Shear Wave Velocity (ft/sec)
  9. 9. Median Vs Profiles for all Geologic Units
  10. 10. Geology – Site Classification Correlations Geology Number of Profiles Median Vs,30m (m/s) NEHRP Site Class( ) Af 3 278 D Qham 3 335 D Qh 2 1 346 DQht2 1 346 D Qphf 2 480 C Qpf 8 499 CQp Ppf 1 504 C Pf 7 564 C b 3 CMpb 3 513 C Lmst 1 1014 B
  11. 11. Seismic Site Classification Map of Port-au-Prince
  12. 12. Some Potential Refinements? Shear Wave Velocity (m/s) 0 0 4003002001000 Shear Wave Velocity (m/s) 20 10 5 S ft 60 40 Depth(ft) 15 Depth(m) Soft Clay??? 80 25 20 Site 100 30 Vs = Vs30 = 250 m/s Class D Site Class D or E? 160012008004000 Shear Wave Velocity (ft/sec)
  13. 13. IBC & ASCE Codes – Seismic Site Classification Vs N SuSite Class: A - F > 1 500 m/s> 1,500 m/s 760 – 1,500 m/s 360 – 760 m/s 180 360 /180 – 360 m/s < 180 m/s ASCE 7-05
  14. 14. Questions?Questions?

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