The use of magnetorheological (MR) dampers in combination with other control devices in a hybrid mode to enhance the control of the seismic responses of building structures is a subject of topical interest. This paper reports on the development of hybrid control schemes using different combinations of MR and tuned mass dampers (TMDs) to control the earthquake responses of building frames. The performance of the hybrid control schemes was evaluated by comparing the results with those of purely semi-active control schemes using three and four MR dampers consecutively placed in the bottom storeys of the frame. For the comparison, responses were obtained using four control strategies, namely a linear quadratic regulator with a clipped algorithm, passive-on, passive-off and a newly developed control strategy called velocity tracking control, which is especially suitable for partially observed states. The study showed that a maximum increase of 40–45% control of response could be achieved using a combination of a TMD and fewer MR dampers.

Optimum semi-active control with a limited number of magneto-rheological (MR) dampers and measurement sensors has certain requirements. Most important of them is the accurate estimation of control forces developed in the MR dampers from the observations made in the structure. Therefore, the observation strategy should form an integral part of the optimization problem. The existing literature on the subject does not address this issue properly. The paper presents a computationally efficient optimization scheme for semi-active control of partially observed building frames using a limited number of MR dampers and sensors for earthquakes. The control scheme duly incorporates the locations of measurement sensors as variables into the genetic algorithm (GA) based optimization problem. A ten-storied building frame is taken as an illustrative example. The optimum control strategy utilizes two well-known control laws, namely, the linear quadratic Gaussian (LQG) with clipped optimal control and the bang-bang control to find the time histories of voltage to be applied to the MR dampers. The results of the numerical study show that the proposed scheme of sensor placement provides the optimum reduction of response with more computational efficiency. Second, optimal locations of sensors vary with the response quantities to be controlled, the nature of earthquake, and the control algorithm. Third, optimal locations of MR dampers are invariant of the response quantities to be controlled and the nature of earthquake.

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