An Overview of Cylindrical Water Tank Buckling Analysis Under Seismic Loading

A thin walled cylindrical liquid storage tank submitted to a large seismic excitation may exhibit buckling. Depending on the geometrical and dynamical characteristics of the tank, two buckling patterns are possible: • a bending buckling characterized by an “elephant foot bulge” at the bottom part, • a shear buckling characterized by oblique waves at the middle part of the tank. In a recent paper (Ref. [1]), Tomohiro I. et al. have presented the Japanese experience about bending buckling of cylindrical water tanks. Dynamic buckling experimental tests were performed using large scale water tank models simulating thin walled cylindrical water tanks in Nuclear Power Plants (NPP). Test results were compared with finite element simulations and the applicability of a simple analytical method included in the AIJ (Architectural Institute of Japan) design guide lines on the buckling of liquid storage tanks was also investigated. In Europe, in the frame of the preparation of Eurocodes, a simple analytical method has also been developed to assess the buckling resistance of liquid storage tanks against seismic solicitations. On the other hand, FRAMATOME-ANP has gained her own experience about buckling analysis of large thin tanks where boric water is stored in French NPP. In order to justify the buckling behaviour of these tanks under extreme seismic loadings (Safe Shutdown Earthquake), finite element elastic-plastic calculations on shell models were undertaken where the influence of manufacturing geometrical defects was taken into account and the results were compared with those given by the simple analytical method included in Eurocode 8. In this paper, French and Japanese methodologies will be recalled and applied to a representative example of nuclear industry. Finally, some advanced aspects of the problem like the post-buckling behavior of the tanks and the influence of a possible bottom uplifting will be developed.