Method for Seismic Base Isolation of Liquid-Storage Tanks

Abstract

A new method for seismic base isolation of ground-supported vertical cylindrical liquid-storage tanks is proposed in which the base plate is supported on a soil bed, and the tank wall is supported on a ring of vertically soft rubber bearings. The isolated system derives its flexibility from rocking and uplifting of the base, and derives its energy-dissipation capacity from base-plate yielding, soil damping, and hysteretic rubber damping. In this analysis, the tank-liquid system is represented by a lumped-mass-stick model, and the rubber bearings are represented by a series of nonlinear hysteretic axial springs. The partially uplifted base plate loaded by liquid is analyzed giving due consideration to the effects of membrane action and plastic yielding. Results demonstrate the ability of the isolation method in reducing significantly the overturning base moments and the axial compressive stresses in the tank wall, while still maintaining the values of base uplifts and plastic rotations in the base plate at reasonable levels.