Seismic response of liquid storage tanks isolated by sliding bearings

The response of liquid storage tanks isolated by the sliding systems is investigated under two horizontal components of real earthquake ground motion. The continuous liquid mass is lumped as convective mass, impulsive mass and rigid mass. The corresponding stiffness associated with these lumped masses is calculated depending upon the properties of the tank wall and liquid mass. The governing equations of motion of the tank with a sliding system are derived and solved by Newmark's step-by-step method with iterations. The frictional forces mobilized at the interface of the sliding system are assumed to be velocity dependent and their interaction in two horizontal directions is duly considered. A parametric study is also conducted to study the effects of important system parameters on the effectiveness of seismic isolation of the liquid storage tanks. The various parameters considered are (i) the period of isolation (ii) the damping of isolation bearings and (iii) the coefficient of friction of sliding bearings. It has been found that the bi-directional interaction of frictional forces has noticeable effects and if these effects are ignored then the sliding base displacements will be underestimated which can be crucial from the design point of view. Further, the dependence of the friction coefficient on relative velocity of the sliding bearings has no significant effects on the peak response of the isolated liquid storage tanks. (C) 2002 Elsevier Science Ltd. All rights reserved.