Influence of isolation system characteristic strength on the earthquake behavior of base-isolated liquid storage tanks

Earthquake performance of liquid storage tanks may be substantially improved by base-isolation. However, the possibility of facing large isolator displacements in case of large magnitude near-fault earthquakes threatens the safety of these structures, which may be realized if the period of the velocity pulses that typically exist in the near-fault earthquake records are close to their isolation periods. Increasing isolation system characteristic strength may help reducing the aforementioned large isolator displacements but this in turn may have a negative impact on the superstructure response. Therefore, this study aims to investigate the influence of the characteristic strength of the isolation system on the behavior of base-isolated liquid storage tanks under representative historical near-fault and far-fault earthquakes by making use of a set of benchmark tank models with different levels of isolation system characteristic strength ratios. Numerical modeling and non-linear time history analyses are carried out via the academic software 3DBASIS-ME,which offers the possibility of conducting such modeling and analysis following a highly preferred mechanical analog that is able to take the deformability of the tank wall and sloshing of the fluid into account by considering the fundamental sloshing and fundamental fluid-tank modes of vibration as single degree of freedom systems sharing a common isolation base-mat. The seismic responses including isolation system displacement, sloshing fluid displacement, isolation system shear force, fluid-tank shear force, and sloshing fluid shear force are reported in a comparative manner. Results show that while higher characteristic strength effectively reduces large base displacements observed under near-fault earthquakes, it may cause significant amplifications in the superstructure responses particularly under far-fault earthquakes.