Response of Flexible Buildings From the 2003 Tokachi-Oki Earthquake

1. Response of Flexible Buildings From the 2003 Tokachi-Oki Earthquake Jing Yang Thomas Heaton John Hall California Institute of Technology

2. Epicenter and fault The 2003 Tokachi-Oki Earthquake Mw 8.3 • Shallow subduction earthquake: • Fault area: 90km*70km, top depth: 20km; bottom depth 60km • Average slip: 2.6m • Maximum horizontal displacement = 0.90 m (From GPS data)

3. Damage of structures in Hokkaido 2003 Buildings are short and strong. Taiki-cho Town Hall School, designed as an evacuation center

4. Current Building Code • Current building codes are mostly prescriptive rules based on the building type and seismic zone. • Codes have been developed by fixing deficiencies from past earthquakes. • If you’ve got a good building code, who needs a seismologist?

5. Who needs a seismologist? • What are the key issues in earthquake hazards. Are we missing anything important? • Large magnitude earthquakes (i.e. infrequent) may be the primary threat to our societies. • Near-source problem … what are the conditions for directivity (killer) pulses? • What do we know about great and giant subduction earthquakes?

6. Key issues for this talk • What is the expected response of flexible buildings to great (M~8) subduction earthquakes located in nearby coastal regions? • What will happen to high-rise buildings in Seattle, Portand, Vancouver, and Jakarta if they are adjacent to a giant (M~9) ? • The 2003 Tokachi-Oki earthquake (Mw8.3) is the largest well recorded earthquake. • US code-compliant high-rise buildings would have been heavily damaged in coastal regions of Hokkaido.

7. KiK-Net and K-Net

8. Erimo ground velocity

9. Erimo ground displacement

10. Samani ground velocity

11. Urahoro ground velocity

12. Urahoro ground displacement

13. Model: 20 story steel moment-frame building • 20 story steel moment-frame building plus one basement. • Designed according to the 1994 UBC • Natural period is 3.5 sec • H=77.88 m Frame Elevation Floor Plan

15. Failure of Welded MRF Connections • Steel beams are intended to plastically yield • Integrity of welded MRF connections is key to applying moments such that the beam yields. • Northridge and Kobe showed that the welded connections fractured before any plastic yielding occurred. That is, the buildings were brittle.

16. US UBC (1994) 20-story steel frame

17. Pushover analysis of 20-story steel MRF buildings (Hall)

18. Pushover analysis of 6-story steel MRF buildings (Hall)

19. Result for 1999 Chi-Chi earthquake Ground Displacement Roof Displacement

20. Maximum dynamic roof displacement for 20-story US building with perfect welds

21. Percent of welded moment connections fractured for US 20-story steel frame

22. Permanent roof displacement for US 20-story steel frame with brittle welds

23. Percent of welded moment connections fractured for US 6-story steel frame

24. Inter-story shear for US 6-story steel frame with brittle welds

25. Permanent roof displacement for US 6-story steel frame with brittle welds

26. Scale factor →

27. Scale factor →

28. Scale factor →

29. Interstory drift as a function of peak acceleration for 20-story US building (brittle welds) … PGA doesn’t say much about building response

30. Interstory drift as a function of peak velocity for 20-story US building (perfect welds) … PGV is a pretty good predictor of building response for a wide variety of building types.

31. Interstory drift as a function of response spectra (averaged from 3 to 5 seconds) for 20-story US building (perfect welds) …PSV is a very good predictor of building response for a flexible building that is relatively far from collapse.

32. Interstory drift as a function of response spectra (averaged from 3 to 5 seconds) for 20-story US building (brittle welds) …PSV is not as good a predictor predictor of building response for a flexible building when the response gets closer to collapse.

38. Are We Addressing the Right Questions in Earthquake Engineering? • Current methodology assumes 1) architecture and 2)seismic hazard. • Very simplified assumptions about nonlinear building response (ductility factors) are used to produce a design. • “collapse mechanisms” are rarely defined. • Earth scientists are almost never asked if it is possible that the site will experience motions that can trigger the collapse mechanisms.

39. Conclusions • In the Tokachi-Oki earthquake, high-rise buildings would have been strongly excited with the potential for collapse in the region around station HKD098. • Stations in basins created significantly higher damage. • Increasing the strength of welded connections significantly improves the response of buildings. • Strong shear-wall construction is best suited to resist large-magnitude earthquakes. • Earth scientists should ask earthquake engineers to provide examples of ground motions that will cause collapse of a particular design. • Choose a design that is least vulnerable to our uncertainties • Seismologists may yet be useful

41. Future Work • Seek better correction scheme to recover true displacement. • Based on the real data, simulate giant subduction earthquakes Mw 9.5 • Use synthetic large ground motion to simulate the response of flexible buildings.