New method for seismic isolation of liquid-storage tanks

Abstract

Seismic base isolation of ground supported cylindrical liquid-storage tanks is proposed by disconnecting the wall of the tank from the base plate and supporting it on a ring of horizontally flexible bearings; the base plate is supported directly on the ground. The gap between the wall and the base plate is closed with a flexible membrane, which prevents the loss of fluid from the tank and allows the tank wall to move freely in the horizontal direction. The effect of isolation on both the impulsive and the convective (sloshing) responses of the liquid is examined for two steel tanks–one broad and one slender. It is shown that isolation can reduce dramatically the hydrodynamic base shears, overturning moments, and axial compressive stresses in the tank wall without significantly increasing the vertical displacements of the liquid surface due to sloshing. Since the weight supported by the bearings is small compared to the total liquid weight, the bearings in slender tanks experience a net tensile force during strong shaking. © 1997 John Wiley & Sons, Ltd.