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Earthquake response of elevated liquid storage steel tanks isolated by the linear elastomeric bearings is investigated under real earthquake ground motion. Two types of isolated tank models are considered in which the bearings are placed at the base and top of the steel tower structure. The continuous liquid mass of the tank is modelled as lumped masses known as sloshing mass, impulsive mass and rigid mass. The corresponding stiffness constants associated with these lumped masses have been worked out depending upon the properties of the tank wall and liquid mass. The mass of steel tower structure is lumped equally at top and bottom. Since the damping matrix of the isolated tank system is non-classical in nature, the seismic response is obtained by the Newmark's step-by-step method. The response of two types of tanks, namely slender and broad tanks, is obtained and a parametric study is carried out to study the effects of important system parameters on the effectiveness of seismic isolation. The various important parameters considered are the tank aspect ratio, the time period of tower structure, damping and the time period of isolation system. It has been shown that the earthquake response of the isolated tank is significantly reduced. Further, it is also observed that the isolation is more effective for the tank with stiff steel tower structure in comparison to flexible towers. In addition, a simplified analysis is also presented to evaluate the response of the elevated steel tanks using two-degrees-of-freedom model and two single-degree-of-freedom models. It is observed that the proposed analysis predicts the seismic response of elevated steel tanks accurately with significantly less computational efforts.

A comparative study of performance of various isolation systems for liquid storage tanks is investigated under real earthquake ground motions. The various base isolation systems considered are the laminated rubber bearings (with and without lead core) and sliding isolation systems (with and without restoring force). The isolated liquid storage tank is idealized with three-degrees-of-freedom associated with convective, impulsive and rigid mass under uni-directional earthquake excitation. Since the force-deformation behaviour of the isolation systems is non-linear, as a result, the equations of motion are solved numerically by step-by-step method. In order to measure the effectiveness of the isolation systems, the seismic response of the isolated liquid storage tanks is compared with the corresponding response of non-isolated tanks. Further, the effectiveness of the isolation is also explored for wide range of practical liquid storage tanks considering the influence of tank aspect ratio. It is observed that the isolation systems are quite effective in attenuating the earthquake acceleration transmitted to the tank, which reduces the design seismic forces significantly. Further, it is also found that the sliding type isolation systems are more effective in controlling the response of liquid storage tanks in comparison to the elastomeric bearings. Among the various sliding systems, the resilient-friction base isolator is found to be most effective for seismic isolation of the tanks.