This paper presents the problem definition for the first generation of benchmark structural control problems for cable-stayed bridges. The benchmark problem is based on the Bill Emerson Memorial Bridge that is currently under construction in Cape Girardeau, Missouri. Construction of the bridge is expected to be completed in 2003. The goal of this study is to provide a testbed for the development of strategies for the control of cable-stayed bridges. Based on detailed drawings, a three-dimensional evaluation model has been developed to represent the complex behavior of the full scale benchmark bridge. The linear evaluation model is developed using the equations of motion generated around the deformed equilibrium position. Evaluation criteria are selected that are consistent with the goals of seismic response control of a cable-stayed bridge. Control constraints ensure that the results are representative of a control implementation on the physical structure. Each participant in this benchmark study is given the task of defining ͑including devices, sensors, and algorithms͒, evaluating, and reporting on their proposed control strategies. These strategies may be either passive, active, semiactive, or a combination thereof. A simulation program is provided to facilitate direct comparison of the capabilities and efficiency of the various control strategies. The problem is available through the internet in the form of a set of MATLAB ® programs and includes a sample control design to guide participants through the benchmark problem.

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This paper documents the results of an experimental study conducted to demonstrate the capabilities of multiple magnetorheological (MR) devices for seismic control of civil engineering structures. A six-story test structure in the Washington University Structural Control and Earthquake Engineering Lab (http://www.seas.wustl.edu/research/quake/) is considered, and four parallel-plate, shear-mode MR dampers are used to control this test structure. Two control devices are installed in the test structure between the base and first floor, and two are installed between the first floor and second floor. The system identification method used to develop a model of the integrated structural system is discussed. This method is an extension of a method successfully used in a previous semi-active experiment. Two semi-active control algorithms including a Lyapunov algorithm and a clipped-optimal algorithm are considered. An El Centro earthquake is used to disturb the system and three amplitude levels. The results indicate that high performance levels can be achieved, and the responses of the semi-active system are significantly better than that of comparable passive systems.