Semi-active modal control for seismic structures with variable friction dampers

The implementation of variable friction dampers for vibration mitigation of seismic structures generally requires an efficient semi-active control law. In this paper, a semi-active modal control method is proposed to determine the controllable clamping force of a variable friction damper. By using the Heaviside function, the feedback gain of the proposed method was modified from that of an active control, so it was able to accommodate the control force constraint of the variable friction dampers. A discrete-time formulation and numerical procedure for the simulation of the proposed control method is discussed. A comparative study was performed on a multiple DOF structure controlled by passive friction dampers, variable friction dampers as well as an active bracing system. Several structural configurations with various damper/sensor deployments were also considered. The study has shown that by merely using a few sensors and a lesser number of dampers than the passive control case, the proposed semiactive control method is able to effectively and simultaneously reduce the average maximum responses of the floor displacements and accelerations. It is also shown that as compared with the control performance of its active control counterpart, the proposed method provides almost equivalent capacity of energy dissipation, and an equal level of response reduction. (C) 2003 Elsevier Ltd. All rights reserved.