Stochastic seismic analysis of base-isolated structures with electromagnetic inertial mass dampers considering different soil conditions

An electromagnetic inertial mass damper (EIMD) is an inerter-based damper that can significantly enhance the seismic performance of a frame structure. However, the stochastic seismic analysis of a base-isolated structure (BIS) with the EIMD subjected to earthquake ground motions has rarely been reported. Based on a probabilistic framework, this paper studies the stochastic seismic responses of the BIS with the EIMD subjected to seismic excitations considering three typical soil conditions. The analytical solutions of the response variances of a two-degree-of-freedom (2DOF) BIS-EIMD system are derived considering both stationary and non-stationary seismic excitations. A parametric study on the BIS-EIMD system subjected to stochastic seismic excitations modeled by filtered Kanai-Tajimi spectrum is conducted to investigate the different seismic responses under firm, medium, and soft soil conditions, and the corresponding optimal inertance and damping of the EIMD are obtained by minimizing the stochastic seismic responses of the superstructure or the base floor. The results of the 2DOF BIS-EIMD system indicate that the optimal EIMD achieves comparable control performance under the three soil conditions, but the optimal parameters of the EIMD vary significantly under different soil conditions. Under soft soil conditions, the BIS-EIMD system requires a much larger inertance setting compared with that of the firm and medium soil conditions. A numerical simulation of a seven-story isolated building with an EIMD is conducted considering both artificial seismic excitations and real earthquake ground motions. Numerical results show that the EIMD is capable of significantly suppressing the seismic responses of both the base floor and the superstructure, which is better than that of a conventional viscous damper.