Assessing Seismic Base Isolation Systems for Liquid Storage Tanks using Fragility Analysis

Abstract

Liquid storage tanks are essential component of petroleum industries, thermal power plants, chemical factories and numerous other important industries along with civil society. Herein, seismic fragility of base-isolated liquid storage tank is evaluated to assess the performance of various base isolation systems in enhancing the seismic protection. The liquid storage tank is modeled using lumped mass mechanical analog. Failure of the liquid storage tank is defined in terms of buckling of the tank wall in elastic range. The maximum displacement at isolation level is also considered in the failure criteria. The equations of motion are solved using Newmark’s method to obtain the peak response quantities of the base-isolated liquid storage tank. Two different configurations, i.e. broad and slender, of the base-isolated liquid storage tanks are chosen for the comparison. Monte Carlo (MC) simulation is used to obtain the probability of failure (p f) at different seismic intensity level. The probability of failure for the slender tank is observed more as compared to the broad tank. The seismic fragility of the base-isolated liquid storage tanks is evaluated considering the randomness in the earthquake ground motion. Seismic performance of fixed-base tanks are compared with the base-isolated tanks in terms of the probability of failure. It is observed that the base isolation enhances the seismic performance of the liquid storage tanks irrespective of the type of isolation system. However, enhancement in the seismic performance of the liquid storage tanks varies significantly for different isolation systems considered in the present study.