Seismic Responses of Innovative Vertically Isolated Liquid Storage Tanks under Near-Fault and Far-Fault Ground Motions

The seismic response of aboveground liquid storage tanks isolated by the proposed vertical isolation system (VIS) is investigated under near-fault and far-fault ground motions. For this purpose, a set of 14 ground motions including seven far-fault and seven pulse-like near-fault motions have been considered. Effectiveness of VIS is evaluated theoretically and numerically in selected tanks with different geometries including Short-Broad, Tall-Broad, Short-Slender, and Tall-Slender. In the proposed isolation system, the tank shell is detached from the base and supported on a ring of vertical isolators, and then the forces in the vertical direction caused by the overturning moment are isolated as an alternative to the common horizontal system used for shear base isolation of storage tanks. The equations of motion for a liquid tank equipped with the proposed system were extracted using the mass-spring simplified model of contained liquid. A study was performed by employing the non-linear solution of the governing equations and the effectiveness of the proposed system for selected tanks is discussed. To measure the effectiveness of the isolation system, the seismic response of isolated steel tanks is compared with that of the non-isolated (or fixed-base) tanks. The results of this study demonstrate the influence of the tank's geometries, characteristics of the isolation system, and input excitation features. These parameters should be reasonably selected to achieve the maximum mitigation of seismic responses in the tanks equipped with the VIS. Excitation parameters, PGV/PGA ratio of input records, and pulse period in two sets of ground motions are defined to recognize the variety of responses. It is confirmed that the VIS performs well under both near and far-fault motions but near-fault earthquakes amplify the seismic responses more than the far-fault records especially in broad tanks.