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Abstract: A common effective method to reduce the seismic response of liquid storage tanks is to isolate them at base using base-isolation systems. It has been observed that in many earthquakes, the foregoing systems significantly affect on the whole system response reduction. However, in exceptional cases of excitation by long-period shaking, the base-isolation systems could have adverse effects. Such earthquakes could cause tank damage due to excessive liquid sloshing. Therefore, the numerical seismic response of liquid storage tanks isolated by bilinear hysteretic bearing elements is investigated under long-period ground motions in this research. For this purpose, finite shell elements for the tank structure and boundary elements for the liquid region are employed. Subsequently, fluid–structure equations of motion are coupled with governing equation of base-isolation system, to represent the whole system behavior. The governing equations of motion of the whole system are solved by an iterative and step-by-step algorithm to evaluate the response of the whole system to the horizontal component of three ground motions. The variations of seismic shear forces, liquid sloshing heights, and tank wall radial displacements are plotted under various system parameters such as the tank geometry aspect ratio (height to radius), and the flexibility of the isolation system, to critically examine the effects of various system parameters on the effectiveness of the base-isolation systems against long-period ground motions. From these analyses, it may be concluded that with the installation of this type of base-isolation system in liquid tanks, the dynamic response of tanks during seismic ground motions can be considerably reduced. Moreover, in the special case of long-period ground motions, the seismic response of base-isolated tanks may be controlled by the isolation system only at particular conditions of slender and broad tanks. For the case of medium tanks, remarkable attentions would be required to be devoted to the design of base-isolation systems expected to experience long-period ground motions. [Copyright &y& Elsevier]

Abstract: The effects of base-isolation on the seismic response of cylindrical vertical flexible liquid storage tanks subjected to horizontal seismic ground motion are presented in this paper. The whole system consists of two main parts: the base-isolation component, and the fluid–structure interaction subsystem. Dynamic analysis of liquid storage tank is achieved through the use of finite shell elements for the structure and internal boundary elements for the liquid region. The boundary element equations are employed to obtain an equivalent liquid mass matrix which is then coupled with the shell structure mass matrix, resulting in the coupled equations of motion. Finally, the coupled equations of motion are connected with the base-isolation system to observe the whole system behavior. A bilinear hysteretic element is used to illustrate the base-isolation system. The analysis is performed in the time domain in which, hydrodynamic interaction is taken into account. It is shown that the seismic response of the isolated tank could be significantly reduced compared with the fixed-foundation tanks. Parametric studies are carried out to study the effects of different system parameters on the effectiveness of the base-isolation system. These parameters are the tank geometry aspect ratio (height to radius), the flexibility of the isolation system, the liquid surface displacement variations, and the tank wall flexibility. It is observed that the seismic isolation is more effective in slender tanks in comparison with broad tanks. Furthermore, it is shown that the isolation efficiency is partially more significant in rigid tanks. It is also noticeable that flexible isolators considerably reduce the seismic response in comparison with stiff isolators. Despite the foregoing advantages, liquid surface displacement increases due to seismic isolation, especially in slender tanks. [Copyright &y& Elsevier]