Seismic Analysis of Base Isolated Liquid Storage Tank

Abstract

A Base-isolation belongs to the passive vibration control device family installed at the base of the structure which dissipates the external excitation energy by reducing the transmitted acceleration into the structure. The earthquake response of the liquid storage tank isolated by sliding and elastomeric bearings systems is studied under ten real existent earthquakes. The continuous liquid mass of the tank is modeled as lumped masses known as impulsive mass, convective or sloshing mass and rigid mass. The coupled dynamic equations of motion for both non-isolated and isolated tanks are solved by using Newmark’s-Beta method considering time interval 0.02 s with iterations. The seismic response of the isolated tank is compared with non-isolated tank to study the effectiveness of base isolation system. The tank isolated by three different isolation systems LRB, Z-N system and R-FBI systems are studied and comparative study also carried between these three systems. A parametric study is also carried out to study the effect of various important system parameters on the effectiveness of seismic isolation for liquid storage tanks. The parameters which are considered as (1) time period of base isolation system (2) damping ratio of base isolation system (3) aspect ration of tank. It was observed that both sliding systems and elastomeric are found to be effective in reducing the seismic forces of the liquid storage tanks. However, the elastomeric bearing with lead core ( i.e. N-Z system) is found better perform in comparison to other systems. There is 60 –80 % , 70 –90 % reduction in base-shear and impulsive displacement response for low frequency and high-frequency earthquakes were observed respectively. The convective displacement was observed 20 –50% higher than that associated with fixed base.