EVALUATION OF AN ACTIVE VARIABLE-DAMPING STRUCTURE

We present a numerical evaluation of the potential improvements in sei smic disturbance rejection to be obtained by using active variable dam ping control in a structure. Using the responses to seismic excitation of an optimally controlled variable structure and of a minimax-optima l designed fixed structure, we obtain an upper bound on the achievable performance and a lower bound on the acceptable performance of a cont rol system for a variable-damping structure. Both of these bounds are relative to an energy-function criterion. Our numerical experiments le ad to the following conclusions: (i) The gap between the upper and low er bounds is rather small, which makes designing a feedback law, that results in performance superior to that of a minimax-optimal designed structure, very difficult. The best choice for a feedback law appears to be continuous moving horizon control, whose implementation requires ground motion prediction up to 0.2 sec ahead, possibly using sensors located a small distance away from the site. (ii) A minimax-optimal de signed structure gives very good seismic disturbance suppression, not only for the earthquakes used in its design, but also for other earthq uakes of similar intensity. Controlled variable structures are likely to offer advantages when earthquakes are moderate to severe, particula rly at sites, such as landfills and dry lake beds, where resonances ca n be expected, but the resonance frequency cannot be estimated in adva nce.