Effect of base isolation on seismic fragility of aboveground LNG storage tanks

Fragility curves of base-isolated and non-isolated LNG storage tanks are developed to investigate the effect of the base isolation design to seismic performance of LNG storage tanks. A non-isolated LNG storage tank is selected and two base isolation designs with respect to acceleration and displacement criteria are applied to this tank. Nonlinear time history analyses of the fixed and two base-isolated models are performed for a suite of 20 ground motions scaled to have a specified PGA. Thresholds based on the crack strain at the base of the concrete tank wall defined the limit states for fragility curves. Finally, empirical fragility curves are fitted by lognormal CDF. Comparison of fragility curves of fixed and base-isolated tanks revealed that the base isolation considerably reduces the risk of damage under a specified level of earthquake. The identified performance demand will be later used for constructing tailor-made base isolation devices.