A semi-active impact damper for multi-modal vibration control under earthquake excitations

A semi-active impact damper (SAID) with controllable timing is presented based on vibro-impact mechanism, aiming to control the multi-modal vibration of civil structures under earthquake excitations. The proper impact actuating force can interfere with the accumulation of structural vibration amplitude without additional controllable dampers. In this paper, the damping performance of the SAID system in a five-story frame structure is studied through shaking table tests and numerical simulation. A series of parametric studies have been conducted to explore the damping mechanism of the system based on analysis of the changeable motion boundary and interaction forces with the main structure. The results show that the SAID system can transfer the structural vibration energy from low-order modes to high-order modes to accelerate the energy dissipation during the controlled impact process, and suppress the structural response caused by dominant modes. Moreover, a parameter sensitivity analysis of the SAID system is investigated, the results show that the damping performance is still efficient when working condition of the semi-active control module changes and the system remains an effective damping behavior under random seismic excitations with more than 40% attenuation effect on root-mean-square structural response in the most cases.