Comparison of Ground Motion Pulse Models for the Seismic Response of Seismically Isolated Liquid Storage Tanks

Abstract

Liquid storage tanks constitute an important portion of the critical infrastructure whose failure in case of an earthquake would lead to significant economic losses. Seismic base isolation is an emerging technology for assuring seismic safety of these critical structures. It reduces the effective seismic forces by shifting the fundamental period of the structural system out of the resonance range via use of laterally flexible isolation system elements. Despite the success of these structures under frequently occurring typical far-fault earthquakes, their behavior under near-fault earthquakes are being questioned recently. Near-fault earthquake records may contain long-period velocity pulses with high amplitudes, which may be close to or even coincident with the periods of isolation systems and/or the period of the sloshing fluid inside the tanks. This may result in unacceptably large isolation system and/or sloshing fluid displacements which would threaten the safety of the isolation system and the tank superstructure. Thus, both engineers and researchers turn to numerical investigations of the behavior of seismically isolated liquid storage tanks under near-fault earthquakes. However, there is a scarcity of the number of recorded near-fault ground motions as of today, and thus, artificially developed near-fault earthquakes, which are also known as pulse models, are being used as an alternative to recorded near-fault earthquakes in evaluating the near-fault behavior of these structures. There is no question that the reliability of the results obtained from such investigations which make use of pulse models would be strongly dependent on how realistic these models are. Therefore, it is deemed necessary to assess the capability of popular, current pulse models in representing the effects of near-fault ground motions on the responses of seismically isolated liquid storage tanks. For this purpose, we compare the structural response parameters, including isolator and sloshing displacements and isolation system and fluid-tank shear forces of a prototype, seismically isolated liquid storage tank under recorded near-fault earthquakes, and their approximate counterpart synthetic pulse models.