Comprehensive nonlinear seismic study and parametric analysis of base-isolated cylindrical liquid storage tanks under near-fault ground motions: Towards optimal isolation design

This study investigates the non-linear seismic response of base-isolated cylindrical liquid storage tanks under the influence of near-fault ground motions. Two categories of ground motion inputs were considered: equivalent pulses and actual pulse-like excitations. Critical parameters, including isolator damping ratios, tank aspect ratios, and pulse periods, were analyzed. The liquid mass of the tank was modeled using a spring-mass system, while the non-linear shear force-deformation behavior of the bearings was captured through the Bouc-Wen model. Seismic responses were computed utilizing the Newmark-Beta method under the assumption of constant average acceleration. The results indicate that near-fault behavior is influenced by multiple factors beyond the initial velocity pulse. The equivalent pulse model provided accurate estimates of vertical free surface displacement and base shear when pulse periods were near the convective mass period ( 0.85 ≤ T c T P , B a k e r ≤ 1 ) and for normalized periods ( 1.11 ≤ T b T P , Baker ≤ 3.33 ) in isolated tanks. Increasing the isolation period reduced base shear, while higher damping ratios (0 % to 10 %) decreased both base shear and vertical free surface displacement. Standard intensity measures such as SED, PGA, and PGV were concluded to be unreliable predictors of base shear and vertical free surface displacement under both types of ground motion. Using the Response Surface Methodology (RSM), optimal isolation periods of 3.67 s for broad tanks and 3.28 s for slender tanks were identified, with damping ratios of approximately 14 %.