Modified H 2 /LQG control algorithm for designing a multi-objective semi-active base isolation system

Abstract

This paper proposes a modified version of H₂/Linear Quadratic Gaussian (H₂/LQG) control algorithm (MH2/LQG) to design effective semi-active base isolation systems with a supplemental magneto-rheological (MR) damper for simultaneously controlling the base drift and acceleration of a structure. In the proposed MH₂/LQG control algorithm, the weighting parameter defined in the semi-active control law is considered variable during the seismic loading and is adjusted at each time step to prevent the device from applying excessive damping force to the structure. As a result, the supplemental control system is designed not only to reduce the base drift of the isolated structure but also to restrict increases that may occur in accelerations imparted to the superstructure due to excessive damping forces. As a numerical example to illustrate the proposed method, an isolated four-story structure is subjected to different earthquake records and the semi-active base isolation system is designed using both H₂/LQG and MH₂/LQG control algorithms. The results show the effectiveness of the proposed MH₂/LQG control algorithm in designing semi-active base isolation systems which can provide a proper simultaneous control of the base drift and floor accelerations. In addition, comparing the performance of the MH₂/LQG and multi-objective H₂/LQG control algorithms shows that while the two design procedures work similarly in mitigating the maximum base drift, the MH₂/LQG control algorithm is more effective in reducing the maximum floor acceleration.