Plastic buckling of oil storage tanks under blast loads

Abstract

This paper deals with the dynamic behavior of cylindrical shells under blast loads, with special reference to plasticity and plastic buckling. Interest in this problem focuses on the response of steel vertical oil storage tanks with a flat roof under a nearby explosion. The problem is modeled using a finite element discretization of the structure, in which the loads are represented by an impulsive pressure which is variable around the circumference. The results for tanks show that, at low pressure levels, there is an elastic shell behavior, and first yield occurs as the peak blast pressure is increased. For subsequent increases of peak pressure, the dimple extends in the area affected by the pressures, so that vertical stripes with plastic material behavior are formed from top to bottom of the shell. For even higher pressures, a global mode develops with large amplitude displacements. The total plastic energy is investigated under increasing peak pressure levels. It is found that a change in slope occurs in total plastic energy versus peak pressure when plasticity spreads in the shell, and this is associated to the development of a plastic buckling mode. Parametric studies show that the main variable affecting the change in behavior of the shell as identified through the total plastic energy depends on the shell thickness and is only marginally affected by the shell height and diameter. These conclusions are valid for squat shells, such as those used in the oil industry, and may not be accurate for taller shells.