Uplifting Response of Unanchored Liquid‐Storage Tanks

A study of the principal effects of base uplifting on the seismic response of laterally excited, unanchored, cylindrical liquid‐storage tanks is made. The analysis is implemented by a procedure that is highly efficient and believed to adequately represent essential aspects of the problem. The method takes due account of the continuously varying area of base contact and the nonlinearities associated with membrane action and plastic yielding in the base plate. Critical responses of representative tanks are evaluated for increasing intensities of an earthquake ground motion, and the effects and relative importance of the problem parameters are highlighted. The response quantities examined include the pseudoacceleration of the system, which controls the magnitude of hydrodynamic pressures, the uplift of the plate at points along its junction with the shell, the plastic rotation at the plate boundary, and the maximum compressive stress at critical points in the tank wall. It is shown that the base uplifting may significantly reduce the hydrodynamic pressures, but this reduction may still be associated with increased axial stresses in the tank wall and large plastic rotations at the junction of the shell and base plate. These actions are particularly prominent for tall, slender tanks.