In recent years, the idea of applying active control as a means of hazard reduction has grown increasingly popular. While research in this area with respect to building structures has advanced considerably in the past decades, its application to large lifeline structures, such as cable-stayed bridges, under earthquake loading has not been addressed extensively.; The objective of this research is to increase the understanding on how the complexities associated with modeling cable-stayed bridges, such as nonlinear behavior and the participation of coupled, high order vibration modes in the bridge's dynamic response, affect the effectiveness of active control schemes. The 316 degree of freedom analytical model studied here is based on the Jindo Bridge located in South Korea. Computational considerations associated with control analyses require the size of the model to be significantly reduced. The IRS, internal balancing, and modal reduction methods are considered as reduced-order modeling techniques. Results show that the modal reduction technique, because of the ability to select only those modes causing the largest force and displacement response, is the most effective for control applications.; The control analysis examines the effectiveness of full state feedback control employing a linear quadratic regulator and the effectiveness of dynamic output feedback control utilizing a Kalman-Bucy filter in attenuating the structure's force time-history response. Results show that significant reductions of the maximum internal forces and the force/displacement response can be achieved through active control. Furthermore, once effective sensor locations have been selected, output feedback control achieves attenuations in the force response equal to 90-97% of those obtained for full state feedback control. Results illustrate that only first order modes need to be controlled to reduce the displacement response; however, higher order modes must be controlled to reduce the force response. This study also shows that actuators are most effective when located towards the center of the bridge. Multiple-support excitation should be considered since it can excite entirely different modes than uniform-support excitation. Special attention must be given to coupled modes since their control can actually increase the structure's force response.
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