In this research, the effect of different design criteria on performance of multiple tuned mass dampers (MTMDs) under earthquake excitation has been studied. For optimal design of MTMDs, the parameters of TMDs are determined based on minimizing an objective function. Two different objective functions including minimizing (a) the Hankel's norm; and (b) the maximum displacement of structure have been selected using Distributed Genetic Algorithms (DGAs) for solving the optimization problem. For numerical simulation, the method has been utilized on an eight-storey shear frame and optimal MTMDs have been designed. Results show that using the Hankel's norm as the objective function has led to design MTMDs which are effective in reducing the root-mean-square (RMS) of structural response under different earthquakes while in reducing the maximum response both design criteria have had the same results. Through numerical analysis the effect of design record, MTMDs mass ratio, TMD's number and stroke length on MTMDs effectiveness has been studied.
This paper presents an effective method to design active mass dampers (AMDs) for mitigating the seismic response of nonlinear frames. The method is based on using the Newmark-based instantaneous optimal control algorithm for designing AMD, as well as using distributed genetic algorithm (DGA) for optimization of the active control system. To this end, an optimization problem has been defined which considers the parameters of the active control system as design variables and minimization of the maximum required control force of AMD as the objective function with some constraints defined on the maximum stroke length of AMD. Also, the effect of design excitation on performance of AMD under testing earthquakes has been studied. To assess the capabilities of the proposed method, a numerical example has been worked out where an AMD has been designed to control the response of an eight-story nonlinear shear building frame with hysteretic bilinear elasto–plastic behavior under white noise and real earthquake excitations. The designed control systems have been tested under a number of scaled and real earthquakes including both near and far-field earthquakes. Controller’s robustness against variations of structural parameters has also been assessed. The results of numerical simulations show the effectiveness, simplicity and capability of the proposed method in designing AMDs for nonlinear frames. Also comparing the performance of AMD system with that of passive tuned mass damper and active tendon control shows that the AMD has been more effective in reducing the seismic response of nonlinear frames under design and different testing earthquakes.
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