Using Nonlinear Control Algorithms to Improve the Quality of Shaking Table Tests

Abstract eng:
Among experimental testing methods the shaking table testing method is one of the most realistic techniques to study the seismic behavior of structural systems or components thereof. Shaking table tests are able to produce nearly realistic prototype conditions, giving important insight into critical issues such as collapse mechanisms, component failures, acceleration amplifications, residual displacements and post-earthquake capacities. Ideally, the specimen tested on a shaking table is excited as it would be during an actual earthquake event. However, due to the nonlinear behavior of the tested specimen and the limitations of the hydraulic control system, the motion of the shaking table is usually different from the commanded motion recorded during an earthquake event. This difference may produce an unintended response of the tested structure; ultimately, it may result in a pre-mature failure of the specimen. Traditional tuning of shaking table control systems has focused on linear control algorithms, where the structural system is assumed to remain linear-elastic and where there are no model uncertainties and disturbances in the system. In this paper, a nonlinear control algorithm, based on the Lyapunov stability theorem, is utilized to control a shaking table test of a nonlinear single degrees-of-freedom system with the goal to account for nonlinear response, model uncertainties and other disturbance affecting the test as the test is being performed. Simulation results indicate that such nonlinear control algorithm can be used to achieve excellent tracking, even when the tested structure behaves nonlinearly. The example also demonstrates the ability of the nonlinear control algorithm to compensate for disturbances, where the actuator force input to the shaking table plant are altered with respect to the force commands that the control algorithm puts out. Thus, the proposed nonlinear shaking table control algorithm is not only a viable alternative, but also a way to significantly improve the quality of shaking table tests.

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