Optimal design and seismic performance of base-isolated storage tanks using friction pendulum inerter systems

The inerter system has been proposed and proven to be effective to improve the seismic performance of baseisolated storage tanks. However, only rubber bearings modelled with linear spring and dashpot are investigated. Considering the special characteristics of the liquid storage tank (i.e., the variable weight), the friction pendulum system whose isolation period is independent on the structural weight is preferred in a base-isolated storage tank. In this study, the traditional friction pendulum system combined with an inerter system, called friction pendulum inerter system (FPIS), is proposed for performance improvement of the base-isolated tank under seismic excitations. A demand-oriented optimum design method in time-domain is proposed for determining the parameters of the inerter subsystem for the tank with FPIS to meet the expected target performance under a representative artificial seismic input. The nonlinear time history analyses are employed in the optimization process, which considers the strong nonlinearity and the states of the stick and slip motion of the FPIS. Optimization cases are illustrated to verify the effectiveness of the optimum design and check the seismic performances of storage tanks with FPISs by nonlinear time history analyses under seven selected seismic input excitations. The results show that the isolation displacements and liquid sloshing heights of storage tanks can be mitigated as expected. The seismic performances of storage tanks, especially the isolation displacements, can be effectively improved. The proposed FPIS is concluded feasible for seismic improvement of base-isolated tanks and the proposed optimum design method is effective.