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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 91
Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros
Paper 179

Seismic Buckling Analysis of Steel Anchored Tanks

M.A. Al-Kashif1, H.M. Ramadan2, A. Rashed2 and M. Haroun3

1Egyptian Synthetic of Engineering, Egypt
2Structural Engineering Department, Cairo University, Egypt
3Faculty of Engineering, American University, Cairo, Egypt

Full Bibliographic Reference for this paper
M.A. Al-Kashif, H.M. Ramadan, A. Rashed, M. Haroun, "Seismic Buckling Analysis of Steel Anchored Tanks", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 179, 2009. doi:10.4203/ccp.91.179
Keywords: steel tanks, seismic, finite element analysis, elephant's foot buckling, tank shell yielding.

Several modes of failure have been observed in steel, cylindrical, liquid storage tanks subjected to earthquake motion. The axi-symmetric bulging behaviour of the shell close to ground level, commonly called an elephant foot buckling, is studied and presented.

The current codes uses the buckling stress to evaluate the buckling capacity of the tanks. The AWWA (American Water Works Association) [1] and API (American Petroleum Association) [2] standards use a modified value of the classical value of elastic buckling under axial load to account for shell imperfections. This value is reduced to account for shell imperfections and also increased to take into consideration the effect of the internal liquid pressure. In the New Zealand guidelines [3], the value of the modified classical buckling stress is compared with an elastic-plastic buckling stress, and the lower of the two stresses is taken as the allowable buckling stress.

A three-dimensional non-linear finite element analysis is performed focusing on the buckling of cylindrical liquid storage tanks subject to earthquake motion. The general purpose software program "MARC" is utilised to perform the analyses taking into account both the geometrical and material non linearity. Non-linear large deformation large strain analysis is considered throughout the study. It was found that the so-called elephant-foot buckling phenomenon is not caused by failure due to buckling. It is however a failure due to yielding of the tank walls due to combined effect of the hoop and axial stress on the tank shell. Consequently, the calculation of the buckling capacity of the tanks should not be based only on a limiting buckling stress. Consequently, a new approach to determine the buckling capacity of the tanks was suggested based on the Von-Mises yield criterion.

American Water Works Association (AWWA), "Welded Steel Tanks for Water Storage", AWWA-D100, Denver, Colorado, 2005.
American Petroleum Institute (API), "Welded Steel Tanks for Oil Storage", API 650, American Petroleum Institute Standard, Washington D.C., 1998.
M.J.N. Priestley, et al., "Seismic Design of Storage Tanks: Recommendations of a Study Group of the New Zealand National Society for Earthquake Engineering", New Zealand, 1986.

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