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PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005

PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005. Treasure Island site. Total model height: 100 m (328 ft) Discretized into 106 elements Lysmer transmitting boundary with incident motion specified as ½ of the outcropping motion given . Model base.

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PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005

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  1. PEER 2G02 – Code Usage Exercise: OpenSees Zhaohui Yang UCSD 2/15/2005

  2. Treasure Island site

  3. Total model height: 100 m (328 ft) • Discretized into 106 elements • Lysmer transmitting boundary with incident motion specified as ½ of the outcropping motion given Model base Elastic half space

  4. G/Gmax and damping curves • Fitted MD/damping curves (blue) were used at UCLA • Measured MR curves (red) were used at UCSD, with higher damping

  5. Rayleigh damping employed: Damping ratio = 1% at 1 Hz and 6 Hz (as measured damping ratio at low strain is about 1%)

  6. Computed acceleration Time Histories (UCSD)

  7. Response Spectrum (5% damping)

  8. Comments on response spectrum • All analyses give similar spectrum shapes. • Compared to rock outcropping motion, response at soil surface is amplified for period > 0.25 sec and de-amplified for period < 0.25 sec. • Nonlinear analysis results are much lower than that of SHAKE at period 0.6-2 sec, due to strong nonlinearity at this soft soil site. • UCLA response is generally higher than that of UCSD, due to lower damping curves used at UCLA.

  9. Profile of maximum shear strain (UCSD) • approximately in proportion to shear wave velocity (Gmax) profile, as lower Gmax -> lower backbone curve -> more nonlinearity -> higher shear strain

  10. Permanent displacement profile after shaking (UCSD) (strong correlation with shear wave velocity (Gmax) profile)

  11. Location with strongest shear stress-strain response (UCSD) • Notice permanent shear strain incurred in a single pulse

  12. Shear stress-strain response at base (UCSD)

  13. Shear stress-strain response near surface (UCSD)

  14. Gilroy site

  15. Total model height: 170.7 m (560 ft) • Discretized into 173 elements • Lysmer transmitting boundary with incident motion specified as ½ of the outcropping motion given Model base Elastic half space

  16. G/Gmax and damping curves • Fitted MD/damping curves (blue) were used at UCLA • Measured MR curves (red) were used at UCSD, with higher damping

  17. G/Gmax and damping curves • Fitted MD/damping curves (blue) were used at UCLA • Measured MR curves (red) were used at UCSD, with higher damping

  18. Rayleigh damping employed: • UCSD: Damping ratio = 3% at 1 Hz and 6 Hz (as measured damping ratio at low strain is about 3%) • UCLA: Damping ratio = 1% at 1 Hz and 6 Hz

  19. Computed Acceleration Time Histories (UCSD)

  20. Response Spectrum (5% damping) Significant surface amplification at 0.13-2 second periods

  21. Comments on response spectrum • All analyses give similar spectrum shapes. • Compared to rock outcropping motion, response at soil surface is amplified for period > 0.13 sec and de-amplified for period < 0.13 sec. • Nonlinear analysis results are similar to that of SHAKE, as this site is more competent (less nonlinearity). • UCLA response is generally higher than that of UCSD, due to lower damping curves used at UCLA.

  22. Profile of maximum shear strain (UCSD) • Strong correlation with shear wave velocity (Gmax) profile.

  23. Permanent displacement profile after shaking (UCSD)

  24. Location with maximum shear stress-strain response (UCSD)

  25. Shear stress-strain response at base (UCSD)

  26. Shear stress-strain response at surface (UCSD)

  27. Influence of Rayleigh damping on surface acceleration

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