Seismic analysis of base-isolated liquid storage tanks

Abstract

Three analytical studies for the seismic response of base-isolated ground supported cylindrical liquid storage tanks under recorded earthquake ground motion are presented. The continuous liquid mass of the tank is modelled as lumped masses referred as sloshing mass, impulsive mass and rigid mass. Firstly, the seismic response of isolated tanks is obtained using the modal superposition technique and compared with the exact response to study the effects of non-classical damping. The comparison of results with different tank aspect ratios and stiffness and damping of the bearing indicate that the effects of non-classical damping are insignificant implying that the response of isolated liquid storage tanks can be accurately obtained by the modal analysis with classical damping approximation. The second investigation involves the analysis of base-isolated liquid storage tanks using the response spectrum method in which the peak response of tank in different modes is obtained for the specified response spectrum of earthquake motion and combined with different combination rules. The results indicate that the peak response obtained by the response spectrum method matches well with the corresponding exact response. However, specific combination rule should be used for better estimation of various response quantities of the isolated tanks. Finally, the closed-form expressions for the modal parameters of the base-isolated liquid storage tanks are derived and compared with the exact values. A simplified approximate method is also proposed to evaluate the seismic response of isolated tanks. The response obtained from the above approximate method was found to be in good agreement with the exact response.