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