SUMMARYShake table testing is an important tool to challenge integrity of structural and non-structural specimens by imposing excitations at their base. When shake tables are loaded with specimens, the interaction between the tables and specimens influences the system dynamics that may result in undesired performance. In order to compensate the effects of the interaction, open loop feedforward compensation methods have been widely used successfully in current practice of table controls, assuming that the specimens remain linear. On the contrary, unsatisfactory signal performances during shake table testing were observed when flexible and heavy specimens experience nonlinear behavior. While lack of high fidelity might be acceptable for the purpose of exploration research of specimens subjected to random excitations, a high fidelity of signal reproduction is necessary for shake table qualification testing where specific target motion is required to challenge the specimens. In this study, a nonlinear tracking control scheme based on the feedback linearization method is proposed for the control of shake tables to simulate target motions at specific locations of test structures, having nonlinear hysteretic behavior. Additionally, a real-time estimator using the extended Kalman filter is adopted and combined with the controller in order to account for the changes and uncertainties in system models due to nonlinearities and yielding caused by extreme excitations. The proposed adaptive tracking control method has been applied to a realistic shake table-structure test setup by means of numerical simulations, and the results show good tracking and estimation performance.

Among several different experimental techniques, used to test the response of structures and to verify their seismic performance, the shake table testing allows to reproduce the conditions of true effects of earthquake ground motions in order to challenge complex model structures and systems. However, the reproduction of dynamic signals, due to the dynamics of the shake table and of the specimen, is usually imperfect even though closed-loop control in a shake table system is used to reduce these errors and obtain the best fidelity reproduction. Furthermore, because of the dynamic amplifications in the specimen, the signal recorded at desired locations could be completely different from the expected effect of shake table motion. This paper focuses on the development of practical shake table simulations using additional 'open loop' feedforward compensation in form of inverse transfer functions (i.e. the ratio of the output structural response to an input base motion in the frequency domain) in order to obtain an acceptable reproduction of desired acceleration histories at specific locations in the specimen. As the first step, a well-known global feedforward procedure is reformulated for the compensation of the table motion distortions due to the servo-hydraulic system. Subsequently, the same concept is extended to the table-structure system to adjust the shake table input in order to achieve a desired response spectrum at any floor of the specimen. Implementations show how such a method can be used in any experimental facility.The table (or platform) supports the specimen during the test. It is constructed to provide high stiffness with minimum weight and typically consists of a rectangular-or square-shapes platform able to reproduce up to six degrees of freedom (DOF) by servo-hydraulic actuators.The actuators apply the force necessary to create the desired table movement during seismic testing. Linear variable differential transformers (LVDT), or equivalent, are usually mounted in each actuator to provide an electrical feedback signal and to indicate the actuator piston rod position. The actuators are equipped with servovalves that control the direction and the amount of fluid flow to the actuators to minimize the difference between the desired (programmed) and the achieved (measured) displacement. The servovalve ports the fluid provided by the hydraulic power system into the appropriate side of the actuator chambers. This causes the piston to move the actuator arm in the desired direction.The control system monitors and generates program command and feedback signals for the control of the test system. Generally, the control is the key element of the whole system and one of the most difficult technical challenges for mechanical engineers [2]. The controller provides the servovalve command in order to obtain a specific position of the actuator and finally the motion of the platform to reproduce earthquake accelerograms. However, reproduction of a dynamic signal is known to remain imperfect [3]. The degree of distor...

The seismic response of suspended ceiling systems that were shaken at the University at Buffalo; University of Nevada, Reno; and E-Defense facilities is critically assessed in this paper. After presenting a brief description of each experiment, the most repetitive damage observations in all experiments are discussed. Fragility curves are developed for ceiling perimeter connectors, supporting elements, and overall performance of ceiling systems by using 346 combinations of ceiling configurations and shake intensities. The key findings of these curves are the insufficient support of the 7/8-in. wall angles, unconservative code design capacity of connections for supporting elements, and early damage of ceiling systems because of ceiling-piping interaction. Acceleration amplification factors of ceiling systems with respect to suspending floor are computed. The amplification factors prescribed by the code were found to be unconservative due to the pounding of panels to the ceiling grids and deck vibration in a vertical direction.

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