A fuzzy-controlled semiactive electromagnetic seismic isolation system for near-fault and far-field motions

Traditional passive seismic isolation systems, with their fixed damping ratios, struggle to simultaneously address the isolation demands posed by near-fault and far-field ground motion. Although these systems demonstrate superior performance in reducing the absolute acceleration response under far-field ground motion, they can lead to excessive displacement in the isolation layer under near-fault ground motion, increasing the risk of system collision. To overcome this limitation, this study proposes a semiactive electromagnetic seismic isolation system (SA-EMSIS) featuring a continuously controllable damping ratio. A prototype of the SA-EMSIS was developed, and a fuzzy logic control algorithm was implemented to adaptively adjust damping in real time, aiming to preserve the isolation efficiency of the passive system during far-field events while effectively mitigating displacement during near-fault events. The fuzzy controller was further optimized using a multi-objective genetic algorithm to balance acceleration and displacement performance across different seismic inputs. Results from shaking table experiments agreed well with their counterparts in theoretical simulations, validating both the accuracy of the SA-EMSIS model and the reliability of the experimental setup. Compared with traditional passive systems, the SA-EMSIS provides more comprehensive seismic isolation, performing well across far-field, weak near-fault, and strong near-fault ground motion. This study highlights the integration of fuzzy logic control with a variable-damping electromagnetic system as a novel and effective approach for real-time semiactive isolation. The proposed approach demonstrates clear advantages in adaptability and control precision, offering a practical solution for protecting structures and equipment under diverse seismic hazards.