Evaluation of an active variable-damping structure

Abstract : We present an evaluation of the potential improvements in seismic disturbance rejection obtained by using active variable damping control in a structure. Using the response to seismic excitation of an optimally controlled variable structure and of a minimax optimally designed fixed structure, we obtain an upper bound on the achievable performance and a lower bound on the acceptability of a control system for a variable damping structure. Our numerical experiments suggest three conclusions. (1) A minimax optimal designed structure gives very good seismic disturbance suppression, not only for the earthquakes used in its design, but also for other earthquakes of similar intensity. (2) The use of variable structure control is not likely to result in smaller maximum interstory drifts than exhibited by a fixed minimax designed structure. (3) The gap between the upper and lower bounds is rather small, which makes designing a feedback law that results in performance superior to that of a minimax designed structure very difficult. The best choice appears to be in the form of a continuous moving horizon control law, using a horizon of under 0.2 seconds. This requires determination of whether local ground motion can be predicted up to 0.2 sec. ahead, using ground motion monitoring sensors located a small distance away from the site.