Seismic performance improvement of base-isolated structures using a semi-active tuned mass damper

Base isolation can achieve a reduction in floor acceleration and inter-story drift. However, it may suffer from excessive displacements under near-fault and far-field earthquakes. To improve the aseismic performance of passive base-isolated structures, in this paper, a semi-active tuned mass damper (STMD) with variable stiffness and damping is presented. A combined control algorithm based on output signals only is developed for the STMD first. Then, the STMD is applied to an eight-story linear base-isolated structure and also a nonlinear one. As for the linear model, which represents a theoretical benchmark, an optimized passive TMD (PTMD) is used for comparison. As for the nonlinear model, lead rubber bearing (LRB) is considered and simulated using the well-known Bouc-Wen model. Eight earthquakes with different spectral characteristics and peak ground amplitudes are chosen, and two PTMDs are optimized for comparison, while one is tuned to the pre-yield period of the base -isolated model and the other is tuned to the post-yield period of the base-isolated model. Numerical results show that, generally, STMD has the best control effect in both linear and nonlinear models. For displacement re-sponses, because STMD can vary its stiffness and damping, it can mitigate the structural first-mode response effectively, and can achieve both top story and isolated level responses reduction. As for acceleration responses of the top story, STMD achieves excellent performance in the structural second-mode acceleration response miti-gation. Therefore, STMD can improve both displacement and acceleration performances of both linear and nonlinear base-isolated structures effectively.