Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Prediction of the Natural Frequency of Pile Foundation System in Sand during Earthquake

사질토 지반에 놓인 지진하중을 받는 말뚝 기초 시스템의 고유 진동수 예측

  • 양의규 (서울대학교 공학연구소) ;
  • 권선용 (서울대학교 건설환경공학부) ;
  • 최정인 (서울대학교 건설환경공학부) ;
  • 김명모 (서울대학교 건설환경공학부)
  • Published : 2010.01.31
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Abstract

It is important to calculate the natural frequency of a piled structure in the design stage in order to prevent resonance-induced damage to the pile foundation and analyze the dynamic behavior of the piled structure during an earthquake. In this paper, a simple but relatively accurate method employing a mass-spring model is presented for the evaluation of the natural frequency of a pile-soil system. Greatly influencing the calculation of the natural frequency of a piled structure, the spring stiffness between a pile and soil was evaluated by using the coefficient of subgrade reaction, the p-y curve, and the subsoil elastic modulus. The resulting natural frequencies were compared with those of 1-g shaking table tests. The comparison showed that the natural frequency of the pile-soil system could be most accurately calculated by constructing a stiffness matrix with the spring stiffness of the Reese (1974) method, which utilizes the coefficient of the subgrade reaction modulus, and Yang's (2009) dynamic p-y backbone curve method. The calculated natural frequencies were within 5% error compared with those of the shaking table tests for the pile system in dry dense sand deposits and 5% to 40% error for the pile system in saturated sand deposits depending on the occurrence of excess pore water pressure in the soil.

말뚝 구조물의 동적 거동을 분석하고 지진파에 대한 공진 안정성을 확보하기 위해서는 고유 진동수를 합리적으로 산정하는 것이 중요하다. 본 연구에서는 간단한 질량 - 스프링 모델을 이용하여 지진 하중을 받는 말뚝 구조물의 고유 진동수를 간편하면서도 효율적으로 예측할 수 있는 방법을 모색하였다. 고유진동수 산정 결과에 큰 영향을 미치는 지반-말뚝 간 스프링 강성을 지반반력상수와 p-y 곡선 그리고 지반 탄성계수 등을 이용하여 결정하고, 이들을 이용하여 계산한 고유진동수를 1g 진동대 실험에서 계측한 고유진동수와 비교한 결과, 지반반력상수를 이용한 Reese(1974) 방법과 동적 p-y 중추 곡선을 이용한 Yang(2009)의 방법을 이용하여 스프링 강성을 산정하는 것이 가장 우수한 결과를 나타내었는데, 건조토에 위치한 말뚝구조물에서는 5% 이내의 오차를 보였으며, 포화토에 위치한 말뚝 구조물의 경우에는 진동 중에 과잉간극수압의 발생여부에 따라 5%에서 40% 사이의 오차를 나타내었다.

Keywords

References

  1. 김재관, 이동근 (2005), 구조동역학제 2판, (주)피어슨에듀케이션코리아, pp.486.
  2. 유민택, 최정인, 김성렬, 김명모 (2009), "l-g 진동대 모형실험의 가진주파수에 대한 상사법칙 개발", 한국지진공학회 춘계학술발표회 논문집, pp. 23-30.
  3. American Petroleum Institute (1987), "Recommended practice for planning, designing and constructing fixed offshore platforms", API Recommended Practice 2A(RP-2A), 17th edn.
  4. Carter, D.P. (1984), "A non-linear soil model for predicting lateral pile response", Rep. No. 359, Civil Engineering Dept. Univ. of Auckland, New Zealand.
  5. Dou, H., and Byrne, P.M. (1996), "Dynamic response of single piles and soil-pile interaction", Canadian Geotechnical Journal, Vol. 33, pp.80-96. https://doi.org/10.1139/t96-025
  6. Feng, S. and Wang, J. (2006), "Research on lateral resistance of pile in saturated sand under shake loading", Proceedings of Sessions of GeoShanghai, pp.490-497.
  7. Han, J.T., Kim, S.R, Hwang, J.I., and Kim, M.M. (2007), "Evaluation of the dynamic characteristics of soil-pile system in liquefiable ground by shaking table tests", 4th International Conference on Earthquake Geotechnical Engineering, Greece Thessaloniki, Paper No. 1340.
  8. Hardin, B.O. (1978), "The nature of stress-strain behavior of soils", Proceedings, Earthquake Engineering and Soil Dynamics, ASCE Pasadena, California, Vol.1, pp.3-89.
  9. Liu, L. and Dobry, R. (1995), "Effect of liquefaction on lateral response of piles by centrifuge model tests", National Center for Earthquake Engineering Research (NCEER) Bulletin, Vol.9, No.1, January, pp.7-11.
  10. National Cooperative Highway Research Program (2001), "Static and Dynamic Lateral Loading of Pile Groups", NCHRP Report 461, Transportation Research Board - National Research Council.
  11. Prakash, S. and Chandrasekaran, V. (1977), "Free vibration characteristics of piles", Proc. Ninth Int. Conf. Soil Mech. Found. Engin., Tokyo, Vol.2. pp.333-336.
  12. Reese, L.C., Cox, W.R. and Koop, F.D. (1974), "Analysis of laterally loaded piles in sand", Proceedings of the VI Annual Offshore Technology Conference, Houston, Texas, 2(OTC 2080), pp.473-685 .
  13. Ting, J.M., Kauffman, C.R, and Lovicsek, M. (1987), "Centrifuge static and dynamic lateral pile behaviour", Canadian Geotechnical Journal, Vol.24, pp.198-207 . https://doi.org/10.1139/t87-025
  14. Yang, E.K. (2009), "Evaluation of dynamic p-y curves for a pile in sand from Ig shaking table tests", Ph.D. Thesis, Seoul National University, Korea, 2009.