Optimal Damping Ratio of Structural Isolation System

Optimal Damping Ratio of Structural Isolation System

Isolation system can cut off the transmission of earthquake energy from the ground to the superstructure but may result in excessive isolation displacement. Therefore, damping plays an important role in isolation system. The performance of an isolation system is worse when the damping is either too large or too small. In this study, damping of isolation system is investigated. Under white-noise excitation, the isolation damping ratio is optimized such that the mean square of the structural absolute acceleration is minimized. Following the optimization procedures, the optimal isolation damping ratio can be easily obtained by solving a fourth degree polynomial equation. The feasibility of the proposed method is illustrated by an isolated structure subjected to 2002 Hualien earthquake. Because the real earthquake acceleration is not white noise, the performance of the isolation system designed from the proposed optimization process is not the best one but very close to the best one in acceleration response. Therefore, the proposed method may be adopted for the preliminary design of the structural isolation system.