Effect of fixed time delay on stability and performance of actively controlled civil engineering structures

Abstract

In this paper, a state-of-the-art review for the fixed time delay of actively controlled civil engineering structures is presented, including the identification of time delay, the effect of time delay on the stability and performance of the controlled structures, and the evaluation 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 new simulation results are presented to show its limitation in practical applications. Further, a method of stability analysis for the critical time delay of MDOF systems equipped with single or multiple actuators is presented along with the simulation results to demonstrate its applications to seismic hazard mitigations. Under earthquake excitations, simulation results for the structural response indicate that the degradation 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 serious for structures with closely spaced vibrational modes, such as a building equipped with an active tuned mass damper. © 1997 John Wiley & Sons, Ltd.