Buckling of steel tanks subject to earthquake loadings

The main objective of this thesis is to identify the critical seismic excitation level and specific buckling modes for anchored steel storage tanks, considering impulsive and sloshing seismic responses. The geometries of the tanks were selected from typical cylindrical tanks in the Caribbean, considering dome, cone, shallow cone, and flat roofs, with aspect ratios (H/D) of 0.40, 0.63, and 0.95. It was assumed that the tanks were filled with a liquid with the density of water, with liquid level to cylinder height ratio (HL/H) between 0.50 and 0.90. A computational methodology was used in this thesis for the evaluation of stability of steel tanks. In the case of the impulsive model, the pressures due to a rigid body translation movement of the tank were determined using the aggregate mass concept, and the flexibility of the shell was included in the total dynamic pressures. The sloshing pressures were determined by modeling the liquid with finite elements, considering both linear and non-linear wave theory. Natural frequencies and corresponding mode shapes, for the impulsive and convective response of the tank-liquid systems, were obtained. Bifurcations and step-by-step non-linear analyses were used to compute static buckling of the tank-liquid systems, subjected to the impulsive and sloshing actions. Non-linear dynamic buckling analyses, considering a horizontal component of an acceleration record from El Salvador (1986) earthquake, were performed for the impulsive and combined impulsive and convective actions. The results showed large differences in the critical loads obtained for the static and the dynamic buckling analyses. The lowest critical dynamic buckling loads were obtained for the tallest (H/D = 0.95) tank, regardless of the HL/H considered. In all cases, the critical load decreased with an increase in the level of liquid. The results show that for anchored tanks, the effect of sloshing can be neglected in buckling studies, if sufficient freeboard has been left in the top of the cylinder.