Simulations of Flexible Buildings in Large Earthquakes

1. Simulations of Flexible Buildings in Large Earthquakes Thomas Heaton (Caltech) Anna Olsen (Caltech) Jing Yang (Caltech) Masumi Yamada (Kyoto Univ.)

2. Key Issues • Modern high-rise buildings and base-isolated buildings have not yet experienced large long-period ground motions (pgd > 1 m). • Is statistical prediction of long period ground motions technically feasible? • Will the design of long-period buildings change dramatically in the next 100 years?

3. Ph.D. Thesis of Anna Olsen, 2008 • collected state-of-the-art simulations of crustal earthquakes • 37 earthquakes, over 70,000 ground motions • 1989 Loma Prieta (Aagaard et al., 2008) • 1906 San Francisco, with alternate hypocenters (Aagaard et other al., 2008) • 10 faults in the Los Angeles basin (Day et al., 2005) • Puente Hills fault (Porter et al., 2007) • TeraShake 1 and 2 (K. Olsen et al., 2006, 2007) • ShakeOut, from Chen Ji • Moment magnitudes between 6.3 and 7.8 • Long-period (T > 2 s) and broadband (T > 1 s) • PGD and PGV calculated from vector of north-south and east-west components

4. Magnitude 7.8 Same slip distribution, three hypocenter locations Long-period PGD exceeds 2 m near the fault Long-period PGV exceeds 1.5 m Simulations by Aagaard and others (BSSA, 2008) 1906 San Francisco Ground Motions

5. John Hall’s design of a 20-story steel MRF building Building U20 1994 UBC zone4 Stiff soil, 3.5 sec. period Building J20 1992 Japan code 3.05 sec period Both designs consider Perfect welds Brittle welds

6. Pushover Analysis Special attention to P-delta instability Story mechanism collapse Frame 2-D fiber-element code of Hall (1997)

7. Severe damage or collapse in many areas • Stronger, stiffer building (J20) performs better than more flexible building (U20) • Brittle weld buildings 5 times more likely to collapse than perfect-weld buildings • Results summarized in Olsen and others (BSSA, 2008)

8. Displacements on Base Isolators • Typical base isolator is 3 sec with a maximum allowed displacement of 40 cm • Nonlinear isolator displacements exceed linear by 20% to 40% (Ryan and Chopra) • Described in Olsen and others (BSSA, 2008)

9. Collapse Prediction Collapse Remain standing

10. All strong motions recorded at less than 10 km from rupture from M>6 From Masumi Yamada

11. Near-source pga’s are log-normal • Same distribution will apply 100 years from now

12. Long-period ground motions are not log normal • A few large earthquakes can completely change the distribution • Cannot predict what the shape of this distribution will look like 100 years from now

13. Ph.D. Thesis of Jing Yang Narrow model Medium model Wide model • Repeat of the giant (M>9) Cascadia earthquake of 1700 • Simulate rock ground motions with 2003 Tokachi-Oki M8.3 rock records as empirical Green’s functions • Include effect of the Seattle basin by a transfer function derived from teleseismic S-waves transect (Pratt and Brocher, 2006)

14. Ground Motion Recordings of the M 8.3 Tokachi-oki earthquake

15. Seattle Basin transfer function for teleseismic S-waves

16. Simulated rock and basin ground motions for medium rupture

17. Roof Displacement U-20 Brittle welds

18. Roof Displacement U-20 Perfect welds

19. Conclusions • Presence of brittle welds significantly degrades performance (2-8 times more likely to collapse) • Very generally, ground motions with PGD > 0.5-1 m and PGV > 1-2 m/s collapse MRFs • Although much of the physics of long-period ground motions is understood, statistical prediction might not be meaningful (or possible) … a few earthquakes of unknown source characteristics will determine the fate of long-period buildings.

21. 20-Story Steel Frame Buildings (UBC94 and 1992 Japan)

22. 6-Story Steel Frame Buildings (UBC94 and 1992 Japan)