A coupled BE-FE-BE study for investigating the effect of earthquake frequency content and predominant period on seismic behavior of base-isolated concrete rectangular liquid tanks

Main purpose of this study is to numerically simulate a three-dimensional soil-structure-liquid interaction problem in order to scrutinize the dynamic behavior of base-isolated concrete rectangular tanks under horizontal seismic excitations. It has been deduced that in many earthquakes, the isolation systems reduce the earthquake effects on structures by lengthening their fundamental natural periods against excessive drifts of the superstructure. However, in exceptional cases of the soil stiffness and shaking frequency, the base-isolation systems could have noxious effects. Therefore, the numerical seismic response of rectangular liquid tank system isolated by bilinear bearings is investigated under three real earthquakes with different frequency characteristics in this paper. To this end, finite shell elements for tank wall and boundary elements for liquid and soil are used. Subsequently, fluid-structure-soil equations of motion are coupled with isolator governing equation in the time domain, to gain the whole system response. For different concrete tanks from slender to broad ones, the variations of base forces, sloshing responses, shell radial displacements, and hydrodynamic pressures are illustrated under various system parameters such as the flexibility of the isolation system and the soil properties, to censoriously scrutinize the effects of various system parameters on the utility of the base-isolators. From the analyses, author has concluded that the base-isolation effect is intimately dependent on the earthquake characteristics and may amplify or control the structural responses.