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Comparative Analysis of Structural Damage Potentials Observed in the 9.12 Gyeongju and 11.15 Pohang Earthquakes

9.12 경주지진 및 11.15 포항지진의 구조손상 포텐셜 비교연구

  • Received : 2018.02.13
  • Accepted : 2018.04.19
  • Published : 2018.04.30

Abstract

In this paper, comparative analysis of the 9.12 Gyeongju and 11.15 Pohang earthquakes was conducted in order to provide probable explanations and reasons for the damage observed in the 11.15 Pohang earthquake from both earthquake and structural engineering perspectives. The damage potentials like Arias intensity, effective peak ground acceleration, etc observed in the 11.15 Pohang earthquake were generally weaker than those of the 9.12 Gyeongju earthquake. However, in contrast to the high-frequency dominant nature of the 9.12 Gyeongju earthquake records, the spectral power of PHA2 record observed in the soft soil site was highly concentrated around 2Hz. The base shear around 2 Hz frequency was as high as 40% building weight. This frequency band is very close to the fundamental frequency of the piloti-type buildings severely damaged in the northern part of Pohang. Unfortunately, in addition to inherent vertical irregularity, most of the damaged piloti-type buildings had plan irregularity as well and were non-seismic. All these contributed to the fatal damage. Inelastic dynamic analysis indicated that PHA2 record demands system ductility capacity of 3.5 for a structure with a fundamental period of 0.5 sec and yield base shear strength of 10% building weight. The system ductility level of 3.5 seems very difficult to be achievable in non-seismic brittle piloti-type buildings. The soil profile of the PHA2 site was inversely estimated based on deconvolution technique and trial-error procedure with utilizing available records measured at several rock sites during the 11.15 Pohang earthquake. The soil profile estimated was very typical of soil class D, implying significant soil amplification in the 11.15 Pohang earthquake. The 11.15 Pohang earthquake gave us the expensive lesson that near-collapse damage to irregular and brittle buildings is highly possible when soil is soft and epicenter is close, although the earthquake magnitude is just minor to moderate (M 5+).

Keywords

Strong motion duration;Peak ground acceleration;Effective peak ground acceleration;Site effect;Irregularity;Piloti-type buildings;Non-seismic

References

  1. U.S. Geological Survey. Available from: https://www.usgs.gov/.
  2. KBS. Estimated damage for Pohang earthquake is estimated at 97.1 billion won. 2017/12/04 10:50, http://md.kbs.co.kr/news/view.do?ncd=3578812.
  3. Lee CH, Park JH, Kim TJ, Kim SY, Kim DK. Damage potential analysis and earthquake engineering-related implications of Sep.12, 2016 M5.8 Gyeongju earthquake. Journal of Earthquake Engineering Society of Korea. 2016 Dec;20(7):527-536. https://doi.org/10.5000/EESK.2016.20.7.527
  4. Earthuqke Engineering Society of Korea Website. Revision of second analysis of Pohang earthquske response spectra. 2017/11/21, http://eesk.or.kr/html/sub07_index.jsp?ncode=a0001No.138.
  5. Shin DH, Hong SJ, Kim HJ. Investigation on effective peak ground accelerations based on the Gyeongju earthquake records. Journal of Earthquake Engineering Society of Korea. 2016 Dec;20(7):425-434. https://doi.org/10.5000/EESK.2016.20.7.425
  6. Trifunac MD, Brady AG. A study on the duration of strong earthquake ground motion. Bulletin of the Seismological Society of America. 1975;65(3):581-626.
  7. KMA, Detailed analysis result of 11.15 Pohang earthquake. Available from: http://web.kma.go.kr/notify/press/kma_list.jsp?bid=press&mode=view&num=1193456.
  8. Philippacopoulos AJ. Recommendations for resolution of public comments on USI (unresolved safety issues) A-40, seismic design criteria. Upton, New York: Div. of Safety Issue Resolution, Brookhaven National Lab.; c1989.
  9. Applied Technology Council. Tentative provisions for the development of seismic regulations for buildings. ATC-3-06 (NBS SP-510). Washington, DC: U.S Government Printing Office; c1978.
  10. Architectural Institute of Korea (AIK). Korean building code and commentary. Seoul: Kimoondang; c2016.
  11. Lee YW. Derivation of estimating formulas for seismic strength of RC frames designed to gravity loads. Journal of the Earthquake Engineering Society of Korea. 2002;6(3):63-71. https://doi.org/10.5000/EESK.2002.6.3.063
  12. Korea Meteorological Administration (KMA). Domestic Earthquake List. Available from: http://www.kma.go.kr/weather/earth quake_volcano/domestic.jsp.

Acknowledgement

Supported by : 국토교통부