A finite element study on fluid-structure-soil interaction effect on seismic response of base isolated tanks

Analysis of simplified models which are commonly used for base isolated tanks that ignore the influence of fluid and supporting soil may yield unrealistic results. The present work is an attempt to overcome the limitations in the earlier studies, i.e., to consider the effect of fluid and wall interaction at the tank wall, as well as the effect of soil and tank at the base in the analysis of isolated tanks. In the current investigation, a finite element model is considered to study a tank isolated with friction pendulum isolators at the base. The influence of fluid on the tank wall and the supporting soil properties on the seismic behavior of the tank were taken into account in the analysis. One-dimensional elements are considered to model the tank walls and base, and two-dimensional elements are considered to idealise the fluid and soil. Time history analysis of the isolated tank is conducted by subjecting the tank to various earthquake records. The various responses considered for the study are base shear, dynamic pressure, isolator displacement, and sloshing displacement. Investigation shows that, the response varies between 30 – 40 % due to consideration of soil characteristics, indicating that considering soil parameters in the analysis significantly affect the seismic response of the isolated tank. Further, the effect of isolator characteristics, such as the friction coefficient of the sliding surface and isolator period, on the influence of soil-structure interaction (SSI) on the response of the tank is also investigated. In addition, the effect of variation in the period of the tank on the effect of SSI is studied. It is observed that the effect of SSI on response of tank is influenced significantly by the friction coefficient and time period of the isolator, time period of the tank and ground motion characteristics. Moreover, considering the effect of SSI in the analysis may be beneficial or detrimental depending upon the properties of the tank, isolator, type of soil and type of earthquake. The results and studies carried out using the proposed model will help to design the isolated tank and to understand the behaviour of the isolated tank better.