Hybrid control of base-isolated structures using nonlinear fluid inerter under near-fault pulse-like ground motions

In order to effectively control the displacement response of the isolation layer without amplifying the acceleration under near-fault pulse-like ground motions, a nonlinear fluid inerter exhibiting piecewise apparent mass and damping characteristics is proposed. The seismic mitigation effects of the nonlinear fluid inerter in direct and series tuning connection configurations are analyzed. Furthermore, the mitigation performance of the two connection configurations is compared with the classic viscous damper based on a comprehensive frequency- and time-domain analysis. The conclusions indicate that compared to the viscous damper and the direct connection configuration, the tuning connection configuration can more effectively control the isolation-layer displacement, albeit at the expense of amplifying the superstructure acceleration response. However, considering the joint control efficacy of both acceleration and displacement, the direct connection configuration delivers the best overall control performance. Meanwhile, the genetic algorithm used to optimize the NFI design parameters exhibits excellent robustness, as it consistently guarantees desirable control effects under parameter perturbations of the isolation layer. Also, time-frequency analysis reveals that both configurations of NFI achieve control by reducing the seismic energy injected into the isolation system and dissipating it efficiently over a wider frequency band.