Performance of a force-restricted viscous mass damper incorporated into base-isolated liquid storage tanks

Base isolation systems have been widely used to protect large liquid storage tanks (LSTs) from the damaging effect induced by strong earthquake events. In the previous study, viscous mass dampers (VMDs) were incorporated into the isolation layer for suppressing the isolator displacement and liquid sloshing responses of baseisolated LSTs under long-period ground motions. However, it was recently concerned that VMDs may degrade the isolation performance under more commonly occurring short-period ground motions because of their excessive dynamic stiffness and control forces at high frequencies. To address this issue, a modified VMD with a force-restriction mechanism, referred to as force-restricted viscous mass damper (FRVMD), was employed to enhance the seismic performance of base-isolated LSTs. The acceleration and control force transmissibility of the FRVMD controlled system was investigated by using the harmonic balance with alternating frequency/time domain (HB-AFT) method, and compared with the traditional damping devices. A base-isolated benchmark LST model was employed as a numerical example to identify the benefits of FRVMDs in protecting base-isolated LSTs from short- and long-period ground motions, where the result showed that the FRVMD can effectively suppress the isolator displacement and liquid sloshing response of base-isolated LSTs without compromising the base shear. Furthermore, parametric studies were conducted to investigate the influence of aspect ratios, isolation periods, and restriction forces of FRVMDs on the seismic response of the controlled LST. It was suggested that the performance of the FRVMD controlled structure was robust against the variation of aspect ratios and isolation periods.