EFFECT OF FIXED TIME-DELAY ON STABILITY AND PERFORMANCE OF ACTIVELY CONTROLLED CIVIL ENGINEERING STRUCTURES

In this paper, a state-of-the-art review for the fixed time delay of a ctively controlled civil engineering structures is presented, includin g the identification of time delay, the effect of time delay on the st ability and performance of the controlled structures, and the evaluati on of the critical time delay. In particular, a critical review of the stability analysis methods currently available for the critical time delay of Multiple-Degree-of-Freedom (MDOF) systems is conducted and ne w simulation results are presented to show its limitation in practical applications. Further, a method of stability analysis for the critica l time delay of MDOF systems equipped with single or multiple actuator s is presented along with the simulation results to demonstrate its ap plications to seismic hazard mitigations. Under earthquake excitations , simulation results for the structural response indicate that the deg radation of the control performance due to the fixed time delay is not significant until the time delay is close to the critical time delay. It is further demonstrated that the time-delay problem is more seriou s for structures with closely spaced vibrational modes, such as a buil ding equipped with an active tuned mass damper. (C) 1997 John Wiley & Sons, Ltd.