Journal of the Earthquake Engineering Society of Korea (한국지진공학회논문집)

Earthquake Engineering Society of Korea (한국지진공학회)
권호 표지
DOI QR코드

DOI QR Code

Reduction Factor for the Site Coefficient of a Building built on a Poor-backfilled Embedded Foundation

뒷채움이 부실한 묻힌기초 위에 세워진 건축물의 지반증폭계수에 대한 저감계수

  • Received : 2011.09.05
  • Accepted : 2011.12.09
  • Published : 2012.02.29
Download PDF
⟨ Previous Next ⟩

Abstract

In this paper, the reduction factors to calculate the site coefficients of an embedded foundation are estimated, considering the effect of a poor backfill for the seismic design of a building built on an embedded foundation. This is determined by utilizing in-house finite element software, P3DASS, which has the capability of horizontal pseudo 3D seismic analysis with nonlinear soil. The 30m thick soil on stiff rock was assumed to be homogeneous, elastic, viscous and isotropic, and equivalent circular rigid foundations with radii of 10-70m were assumed to be embedded 0, 10, 20, and 30 m in the soil. Seismic analyses were performed with 7 bedrock earthquake records de-convoluted from the outcrop records; the scaling of the peak ground accelerations were to 0.1 g. The study results show that the site coefficients of a poor-backfilled foundation are gradually reduced as the foundation embedment ratio increases, except in the case of a small foundation embedded deeply in the weak soft soil. In addition, it was found that the deviation of the site coefficients due to the foundation size was not significant. Therefore, the typical reduction factors of an embedded foundation with poor backfill are proposed in terms of the shear wave velocity and site class. This is in order to find the site coefficients of an embedded foundation by multiplying the reduction factor by a site coefficient of a surface foundation specified in the design code. They can then be interpolated to determine the intermediate shear wave velocity.

이 논문에서는 뒷채움이 부실한 묻힌기초 위에 세워진 건축물의 지반증폭계수에 대한 기초묻힘으로 인한 저감계수를 산정하기 위한 연구를 비선형 의사 3D 수평지진해석이 가능한 P3DASS 유한요소 프로그램으로 수행하였다. 지반은 30m 두께로 균질하고 탄성과 점성이 있는 등방성 지반으로 단단한 암반 위에 놓인 것으로 가정하였고, 기초는 반경이 10-70m인 등가원형 강체기초로 기초묻힘은 0, 10, 20, 30m인 경우를 고려하였다. 지진해석은 노두에서 실측한 7개 지진기록의 유효지진가속도를 0.1g로 조정한 후 연약지반밑 암반에서의 지진기록을 생성하여 수행하였다. 연구 결과에 의하면, 매우 연약한 지반에 깊게 묻힌 뒷채움이 부실한 소형기초인 경우를 제외하고는 지반증폭계수가 기초묻힘비가 깊어 질수록 점진적으로 감소하고 기초크기에 따른 편차는 크지 않은 것으로 평가되었다. 따라서 뒷채움이 부실한 묻힌기초의 지반증폭계수를 설계기준에 주어진 지표면기초의 지반증폭계수에 곱해서 구할 수 있는 표준저감계수를 전단파속도와 지반종류에 따라 제안하였다. 이 표준저감계수는 지반의 평균전단파속도에 따라 보간하여 사용할 수도 있다.

Keywords

References

  1. International Building Code Council (IBC), 2009 International Building Code (IBC2009), 340-366, 2009.
  2. 대한건축학회, 건축구조설계기준 (KBC2009), Architectural Institute of Korea, Korean Building Code(KBC), Seoul, 2009.
  3. 김용석, 구조물-지반 상호작용과 지진해석, 한국지진공학회, 구미서관, Seoul, 59-69, 2010.
  4. 윤종구, 김동수, 방은석, "국내 지반특성에 적합한 지반분류 방법 및 설계응답스펙트럼 개선에 대한 연구(III)," 한국지진공학회 논문집, 제10권, 제2호, 63-71, 2006. https://doi.org/10.5000/EESK.2006.10.2.063
  5. Zhang, Y., Conte, J.P., Yang, Z., Elgamal, A., Bielak, J., and Acero, G., "Two-Dimensional Nonlinear Earthquake Response Analysis of a Bridge-Foundation-Ground System," Earthquake Spectra, Vol. 24, No. 2, 343-386, 2008. https://doi.org/10.1193/1.2923925
  6. Kim, Y.S., Dynamic Response of Structures on Pile Foundations, Ph.D. Dissertation, The University of Texas at Austin, 1987.
  7. Kim, Y.S., and Roesset, Jose M., "Effect of Nonlinear Soil Behavior on the Inelastic Seismic Response of a Structure," The International Journal of Geomechanics, Vol. 4, No. 2, 104-114, June 2004. https://doi.org/10.1061/(ASCE)1532-3641(2004)4:2(104)
  8. 김용석, "KBC 내진설계기준을 위한 지반분류와 지반계수에 대한 연구," 한국지진공학회 논문집, 제11권, 제1호, 59-65, 2007. https://doi.org/10.5000/EESK.2007.11.1.059
  9. 김용석, "건축물의 지진해석을 위한 연약지반에 묻힌 기초로 인한 지반증폭계수에 대한 저감계수," 한국지진공학회 논문집, 제14권, 제4호, 1-15, 2010. https://doi.org/10.5000/EESK.2010.14.4.001
  10. Kausel E., Forced Vibrations of Circular Foundations on Layered Media, Research Report R74-11, Department of Civil Engineering, MIT, 1974.
  11. Roesset, J.M., A Review of Soil-Structure Interaction, Lawrence Livermore Laboratory, 125, 1980.
  12. PEER Strong Earthquake Data Base, http://peer.berkeley.edu/ smcat/search.html/
  13. Jose, M. Roesset, and Kim, Y.S., "Specification of Control Motions for Embedded Foundations," Proceeding of the 5th Canadian Earthquake Engineering Conference, 63-86, Ottawa, Canada, July 1987.
  14. Dobry, R. et al., "New Site Coefficients and Site Classification System Used in Recent Building Seismic Code Provisions," Earthquake Spectra, Vol. 16, No. 1, 41-67, Feb. 2000. https://doi.org/10.1193/1.1586082
  15. Borcherdt, R. D., "Estimates of site-dependent response spectra for design (methodology and justification)," Earthquake Spectra, Vol. 10, No. 4, 617-653, 1994. https://doi.org/10.1193/1.1585791