The vertical component of ground motions can affect the seismic performance of reinforced concrete (RC) piers as significant as its horizontal counterpart. However, real-time testing for RC piers subjected to both horizontal and vertical ground motions has been scarcely conducted due to the difficulty in multi-axial control of actuators. In this study, the seismic response of a bridge RC pier was investigated by conducting real-time hybrid simulation (RTHS), where the RC pier was physically tested in the laboratory and the bridge superstructure was numerically modeled. The test setup that can synchronously apply both horizontal and vertical ground motions was constructed by using three dynamic actuators and a flexible loading beam (FLB). The lateral response of the RC pier was investigated by varying the intensities for vertical ground motions, while the same intensity for horizontal ground motion is used. It was found that the axial force from the dead load of superstructure can significantly affect the initial stiffness, strength, and post-yield response of the RC pier. For the selected earthquake ground motions, however, the intensity of vertical ground motion did not make a substantial difference in the lateral response, although there was a notable difference in the fracture pattern.

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Structural testing often involves the use of servo-hydraulic actuators. The inherent nonlinearity of a servo-hydraulic actuator as well as the nonlinear response of experimental specimens results in an amplitude-dependent behavior of the entire servo-hydraulic system, making it difficult to accurately control the actuator. The existence of the nonlinear response in the servo-hydraulic system can be a critical issue that must be addressed to achieve a successful real-time hybrid simulation involving a large-scale experimental substructure controlled by multiple actuators. In order to achieve improved control of servo-hydraulic systems with nonlinearities, an adaptive time series (ATS) compensator is introduced in this paper. The ATS compensator continuously updates the coefficients of the system transfer function during a real-time hybrid simulation using on-line real-time linear regression analysis. Unlike most existing adaptive methods, the system identification procedure of the ATS compensator does not involve user-defined adaptive gains. Through the on-line updating of the coefficients of the system transfer function, the ATS compensator can effectively account for nonlinearities in the servo-hydraulic system and experimental specimen, resulting in improved accuracy in actuator control. In this study, the exceptional performance achieved in actuator control using the ATS compensator is demonstrated through a real-time hybrid simulation of a large-scale 3-story steel frame structure with large-scale magneto-rheological (MR) dampers.

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