Shaking Table Tests on Variable Damping Semi-active Control of Base-Isolated Steel Frame Structures Under Ground Motions

To improve the seismic behavior of base-isolated steel frame structures under ground motions with different frequency characteristics, a new semi-active control method, namely, wide-band frequency weighted variable damping control (WFVC), is proposed. It varies the damping of the isolation layer during the excitation by considering the influences of a wide band of frequency components of the ground motion to the fundamental isolation mode as well as the important high frequency modes of the base-isolated structure using a newly proposed transmissibility weighted fast Fourier transform spectrum. A series of shaking table tests of a semi-active controlled four-story base-isolated steel frame structure with an MR damper were conducted. The test results show that the proposed WFVC method could detect the frequency information of the ground motion accurately and evaluate its influence on the structural responses and consequently tune its damping to an optimal manner. Compared with the passive high-damping control and passive low-damping control, the proposed WFVC could realize an optimal control for the base-isolated structure between the two passive cases for all considered ground motions with different frequency characteristics. Compared with the dominant frequency dependent on-off variable damping control, the control performance of the proposed WFVC method could be improved by about 30% under ground motions with uniform frequency characteristics. The study shows that the application of the proposed WFVC can effectively improve the isolation performance of base isolated steel frame structures under ground motions with different frequency characteristics.