Experimental investigation of an electromagnetic seismic isolation system with different configurations of inertance

Protecting seismic isolated equipment or buildings in a near-fault area is challenging because of the strong long-period velocity components of near-fault ground motions. These long-period pulses can cause excessive base displacement of conventional seismic isolation systems. In this study, an electromagnetic seismic isolation system with flywheels (EMSIS-FW) was experimentally investigated to reduce the base displacement of isolation systems during near-fault earthquakes. The EMSIS-FW consists of a sliding platform and rotary electromagnetic (EM) dampers, which can provide an EM damping force. With an additional flywheel installed on each EM damper, its moment of inertia can offer a considerable inertance for the EMSIS-FW. The inertance generated by the flywheel can be hundreds of times larger than its mass. Accordingly, the isolation frequency can be adjusted using different-sized flywheels. A prototype EMSIS-FW was designed and manufactured. A theoretical model was also developed to predict its dynamic behavior. Through shaking table tests, this study provided experimental verification of the effectiveness of inertance on isolation systems subjected to near-fault ground motions. The experimental results indicate that an increase in inertance reduces the isolation displacement, but it may increase the isolation acceleration during a typical far-field ground motion. In addition, the accuracy of the theoretical model was verified using the shaking table test.