This series includes technical reports prepared by faculty, students and staff who are associated with the John A. Blume Earthquake Engineering Center at Stanford University. While the primary focus of Blume Center is earthquake engineering, many of the reports in this series encompass broader topics in structural engineering and materials, computational mechanics, geomechanics, structural health monitoring, and engineering life-cycle risk assessment. Each report includes acknowledgments of the specific sponsors for the report and underlying research. In addition to providing research support, the Blume Center provides administrative support for maintaining and disseminating the technical reports. For more information about the Blume Center and its activities, see https://blume.stanford.edu.
In structural engineering, the mitigation of damage induced by large environmental loads is of paramount interest. Specifically, in seismic regions, earthquakes can pose a threat to human lives and the infrastructure. In recent years, the idea of applying active control as a means of hazard reduction has grown increasingly popular. In essence, through the application of actuators and sensors, active control can reduce structural forces and vibrations such that desirable performance characteristics are achieved. 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 overall 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, without loss of the important vibration characteristics and complexities. Three separate reduced-order modeling techniques for creating effective control models are studied: the IRS method, the internal balancing method, and a modal reduction method. These methods are studied and compared on their ability to capture the complex dynamic response of cable-stayed bridges subjected to multiple-support excitation and their ability to create viable and computationally sound state space models for control analyses. 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 (LQR) and the effectiveness of dynamic output feedback control utilizing a Kalman-Buey 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 performs very well. Attenuations in the force response equal to approximately 90-97% of those obtained for full state feedback control can be achieved. An investigation of various actuator configurations leads to the conclusion that actuators are most effective when located close to the center of the bridge span. The impact of higher order modes and multiple-support seismic excitation on the control of the bridge is also studied. Generally, only first order modes need to be controlled to reduce the displacement response; however, the control of higher order modes is essential to reduce the force response. Multiple-support excitation needs to be considered since it can excite entirely different modes than uniform-support excitation. Moreover, multiple support excitation induces forces that are caused by pseudo-static displacements and can not be controlled. Special attention needs to be given to coupled modes since their control can lead to an increased force response of the structure..Although all results are obtained for the Jindo Bridge, the results remain valid far other cable-stayed bridges, as they typically exhibit similar structural dynamics.
Schemmann, AG and Smith, HA. (1997). Modeling and Active Control of Cable-Stayed Bridges Subject to Multiple-Support Seismic Excitation. John A. Blume Earthquake Engineering Technical Report 123. Stanford Digital Repository. Available at: http://purl.stanford.edu/xp493yh8925
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