Abstract    In the present work, the effect of Soil-Structure Interaction (SSI) in low frequency structures resting on loose soil, through numerical modelling and shaking table tests have been studied. In theoretical studies two types of models namely fixed base and flexible base structure were subjected to three selected earthquake records. Nonlinear dynamic analysis was employed for all of the numerical models. Geometrical and material nonlinearities were considered in all models and finite element method was used for soil modelling. To verify the outputs of the numerical modelling, shaking table tests were carried out. For experimental tests, scaled form of the main structure according to scaling laws, and laminar shear box as a container of the soil, was built. By comparison between the numerical modelling and the shaking table tests results, good agreement was observed. Therefore, the numerical modelling approach was validated. In next step by implementing this approach, comparison between the fixed base and the flexible base results was carried out. In this study, it was demonstrated that considering the SSI effects on structures resting on loose soils increases the lower story drifts. Besides if the structure is located in sites which is susceptible to experience strong earthquakes, this increase is dominant. Therefore negelecting SSI effects leads to unsafe design of the structure.

Keywords    Soil-Structure Interaction, Fully nonlinear analysis, Shaking table tests, Laminar Shear Box

چکیده    دراین پژوهش اثر اندرکنش خاک وسازه برای سازه­هایی با فرکانس ارتعاشی پایین، که برروی خاک سست قرار دارند، به صورت تئوریک و آزمایشگاهی مورد بررسی قرار گرفته است. مدل‌‌های عددی شامل دو دسته می‌‌باشند: سازه با بستر صلب و سازه با بسترانعطاف پذیر، که همگی تحت سه رکورد زلزله منتخب قرار گرفتند. تحلیل دینامکی غیر خطی برروی تمامی مدل‌‌های عددی صورت پذیرفت. در تمامی مدل­ها رفتار غیر خطی هندسی و رفتار غیرخطی مواد منظور شد. به منظور مدلسازی خاک از روش اجزا محدود استفاده گردید. به منظور راستی آزمایی نتایج مدلسازی عددی، آزمایشات میز لرزه انجام شد. سازه مدل آزمایشگاهی، بر اساس قوانین حاکم بر مقیاس بندی ساخته شد. جعبه برشی لایه‌‌ای برای منظورکردن خاک در مدلهای آزمایشگاهی میز لرزه، ساخته شد. مقایسه نتایج مدلسازی‌‌های عددی و تست‌‌های آزمایشگاهی موید انطباق قابل قبول آنها می‌‌باشد. در نتیجه روش مدلسازی عددی به کاررفته معتبر شناخته شد. در مرحله بعد با بهره­گیری از این روش جهت مدلسازی عددی، مقایسه بین مدل‌‌های تئوریک دو دسته سازه (سازه­های با بستر صلب و سازه‌‌های با بستر انعطاف پذیر) صورت پذیرفت. در این تحقیق نشان داده شد که در نتیجه منظور کردن اثر اندرکنش خاک و سازه برای سازه­هایی که روی خاک سست قرار دارند، دریفت طبقات تحتانی افزابش می­یابد. این افزایش در مورد سازه­هایی که علاوه بر سست بودن خاک بستر، مستعد تجربه زلزله­های شدید نیز می­باشند، به اندازه­ای است که نادیده گرفتن اثر اندرکنش خاک و سازه منجر به طراحی غیر­ایمن سازه می­گردد.

References    1.      Wolf, J.P., "Simple physical models for foundation dynamics", Developments in Geotechnical Engineering,  Vol. 83, (1998), 1-70. 2.      Dutta, S.C. and Roy, R., "A critical review on idealization and modeling for interaction among soil–foundation–structure system", Computers & Structures,  Vol. 80, No. 20, (2002), 1579-1594. 3.      Roesset, J.M. and Ettouney, M.M., "Transmitting boundaries: A comparison", International Journal for Numerical and Analytical Methods in Geomechanics,  Vol. 1, No. 2, (1977), 151-176. 4.      Kocak, S. and Mengi, Y., "A simple soil–structure interaction model", Applied Mathematical Modelling,  Vol. 24, No. 8, (2000), 607-635. 5.      Kramer, S.L., "Geotechnical earthquake engineering prentice hall", New York,  (1996). 6.      Hosseini, S.M.M.M. and Pajouh, M.A., "Comparative study on the equivalent linear and the fully nonlinear site response analysis approaches", Arabian Journal of Geosciences,  Vol. 5, No. 4, (2012), 587-597. 7.      Gazetas, G. and Mylonakis, G., "Seismic soil-structure interaction: New evidence and emerging issues",  (1998), 1119-1174.. 8.      Dutta, S.C., Bhattacharya, K. and Roy, R., "Response of low-rise buildings under seismic ground excitation incorporating soil–structure interaction", Soil Dynamics and Earthquake Engineering,  Vol. 24, No. 12, (2004), 893-914. 9.      Azarbakht, A. and Ashtiany, M.G., "Influence of the soil‐structure interaction on the design of steel‐braced building foundation", in Aip Conference Proceedings, AIP. Vol. 1020, (2008), 595-601. 10.    Tavakoli, H., Naeej, M. and Salari, A., "Response of rc structures subjected to near-fault and far-fault earthquake motions considering soil-structure interaction", International Journal of Civil and Structural Engineering,  Vol. 1, No. 4, (2011), 881-896. 11.    Yan, L. and Byrne, P.M., "Application of hydraulic gradient similitude method to small-scale footing tests on sand", Canadian Geotechnical Journal,  Vol. 26, No. 2, (1989), 246-259. 12.    Fishman, K., Mander, J. and Richards, R., "Laboratory study of seismic free-field response of sand", Soil Dynamics and Earthquake Engineering,  Vol. 14, No. 1, (1995), 33-43. 13.    Jafarzadeh, B., "Design and evaluation concepts of laminar shear box for 1g shaking table tests", in Proceedings of the 13th world conference on earthquake engineering, Vancouver, paper. (2004). 14.    Meymand, P.J., "Shaking table scale model tests of nonlinear soil-pile-superstructure interaction in soft clay, University of California, Berkeley,  Vol. 1,  (1998). 15.    Lu, X.-l., Li, P.-z., Chen, Y.-q. and Chen, B., "Shaking table model testing on dynamic soil-structure interaction system", in Proc., 13th World Conf. on Earthquake Eng., (2004). 16.    Tabatabaiefar, H.R. and Mansoury, B., "Detail design, building and commissioning of tall building structural models for experimental shaking table tests", The Structural Design of Tall and Special Buildings,  Vol. 25, No. 8, (2016), 357-374. 17.    Dietz, M. and Muir Wood, D., "Shaking table evaluation of dynamic soil properties", in Proceedings of 4th international conference on earthquake geotechnical engineering., (2007). 18.    Ishimura, K., Ohtsuki, A., Yoloyama, K. and Koyanagi, Y., "Sway-rocking model for simulating nonlinear response of sandy deposit with structure", in Proceedings of the Tenth World Conference on Earthquake Engineering., (1992), 1897-1903. 19.    Guoxing, C., Su, C., Xi, Z., Xiuli, D., Chengzhi, Q. and Zhihua, W., "Shaking-table tests and numerical simulations on a subway structure in soft soil", Soil Dynamics and Earthquake Engineering,  Vol. 76, (2015), 13-28. 20.    Rocha, M., "The possibility of solving soil mechanics problems by the use of models, Laboratório Nacional De Engenharia Civil.,  (1958). 21.    Moncarz, P.D. and Krawinkler, H., "Theory and application of experimental model analysis in earthquake engineering, Stanford University,  Vol. 50,  (1981). 22.    Iai, S., "Similitude for shaking table tests on soil-structure-fluid model in 1g gravitational field", Soils and Foundations,  Vol. 29, No. 1, (1989), 105-118. 23.    Rayhani, M. and El Naggar, M.H., "Numerical modeling of seismic response of rigid foundation on soft soil", International Journal of Geomechanics,  Vol. 8, No. 6, (2008), 336-346. 24.    Itasca Consulting Group, “FLAC2D: Fast Lagrangian Analysis of Continua, version 6.0, User’s manual”, Minneapolis, (2008). 25.    Hardin, B.O. and Drnevich, V.P., "Shear modulus and damping in soils: Design equations and curves", Journal of Soil Mechanics & Foundations Div,  Vol. 98, No. sm7, (1972). 26.    Lysmer, J. and Kuhlemeyer, R.L., "Finite dynamic model for infinite media", Journal of the Engineering Mechanics Division,  Vol. 95, No. 4, (1969), 859-878. 27.    ASCE/SEI 7-10, ASCE standard., "Minimum Design Loads for Buildings and other Structures", American Society of Civil Engineers, (2006). 28.    ., F.E.M.A., Recommended seismic design criteria for new steel moment frame buildings. 2000, FEMA-350, SAC Joint Venture Washington, DC. 29.             Tabatabaiefar, S.H.R., Fatahi, B. and Samali, B., "Numerical and experimental investigations on seismic response of building frames under influence of soil-structure interaction", Advances in Structural Engineering,  Vol. 17, No. 1, (2014), 109-130.