Abstract: The buckling of tank wall of large-scale oil tank is the elastoplastic instability phenomenon subjected to seismic loading. In order to explore the effect of foundation settlement on the buckling strength of unanchored storage tanks, the buckling behaviors of the tank were analyzed using the finite element computer by means of nonlinear stabilization algorithm. Various items of actual geometrical structure were presented thoroughly in the 3D finite element model(FEM), including concrete ringwall foundation of tank, unanchored bottom with slope, shell tapering from the base to the top, wind girders and supports, top angles, stiffening rings and support plates. Geometric nonlinearity, nonlinear boundary conditions and elastic plastic material of Ramberg-Osgood model were involved simultaneously in simulate course. The impacts of hydrodynamic pressure of liquid in the tank under horizontal seismic forces and the number and amplitude of foundation harmonic settlement on the buckling critical compressive stress were researched. The results show that the tank walls between stiffening rings will are prone to axial buckling by the action of foundation harmonic settlement and hydrodynamic pressure of the liquid, that the deformation of tank shells appears aperiodically, that the foundation harmonic settlement and hydrodynamic pressure of the liquid have a negative influence on tank shell buckling critical load, and that the resistance capacity reduces as the harmonic order number rises under the same settlement.

Key words: unanchored storage tank, foundation harmonic settlement, horizontal seismic forces, buckling, tank shell