Real-time hybrid simulation combines experimental testing and numerical simulation by dividing a structural system into experimental and analytical substructures. Servohydraulic actuators are typically used in a real-time hybrid simulation to apply command displacements to the experimental substructure(s). Servohydraulic actuators may develop a time delay due to inherent actuator dynamics that results in a desynchronization between the measured restoring force(s) and the integration algorithm in a real-time hybrid simulation. Inaccuracy or even instability will occur in a hybrid simulation if actuator delay is not compensated properly. This paper presents an adaptive compensation method for actuator delay. An adaptive control law is developed using an error tracking indicator to adapt a compensation parameter used in the proposed compensation method. Laboratory tests involving large-scale real-time hybrid simulations of a single degree of freedom moment resisting frame with an elastomeric damper are conducted to experimentally demonstrate the effectiveness of the proposed adaptive compensation method. The actuator tracking capability is shown to be greatly improved and exceptional experimental results are still achieved when a good estimate of actuator delay is not available.

Superelastic shape memory alloys (SMAs) have inherent properties of complete recovery of large deformation and satisfactory energy dissipation under cyclic loadings. Such properties have attracted wide attention within the earthquake engineering community, especially for the perspective of developing self-centering (SC) structures. SMA braced frames (SMABFs) have emerged in recent years as one of promising SC frames. This paper presents a seismic design methodology for SMABFs using the hysteretic energy spectrum. The underlying principle for the proposed design methodology is that both the total hysteretic energy and accumulated ductility demands in earthquake resistant structures are correlated with the maximum endured deformation. With the quantitative relationship, the seismic performance target, such as the maximum interstory drift ratio, can be readily achieved. The spectra of hysteretic energy and accumulated ductility demands are first constructed in this study for the single-degree-of-freedom (SDOF) systems which represent the global behavior of SMABFs. The SDOF system based results were then utilized for the development of an iterative design procedure for multistory SMABFs. Both 3- and 6-story SMABFs are designed for representative low-to-medium rise building structures and subjected to a suite of earthquake ground motions scaled to the design basis earthquake (DBE) and maximum considered earthquake (MCE) seismic hazard levels. Computational simulation results show that the designed SMABFs satisfy the performance target very well. The proposed methodology is demonstrated to be effective and efficient for seismic design of SMABFs, but could also shed light on other SC structures.

Real-time hybrid simulation provides an economical and efficient experimental technique for performance evaluation of structures under earthquakes. A successful real-time hybrid simulation requires accurate actuator control in order to achieve reliable experimental results. The time delay as a result of servohydraulic dynamics, if not compensated for properly, would lead to inaccurate or even unstable simulation results. However, the nonlinearities in servohydraulic systems and experimental substructures make the actuator delay difficult to accurately estimate in practice. Therefore, actuator control presents a challenge for the application of the real-time hybrid simulation technique to earthquake engineering research. This paper presents an improved adaptive inverse compensation technique for real-time hybrid simulation. Two adaptive control laws based on a synchronization subspace plot are introduced to adjust the compensation parameters in order to minimize both phase and amplitude errors in the servohydraulic actuator response. The improved adaptive inverse compensation method is experimentally evaluated through real-time tests involving a large-scale magneto-rheological damper subjected to band-limited white noise–generated random displacements and variable current inputs. The experimental results are compared with the command displacements, with the error assessed using various evaluation criteria. The improved adaptive inverse compensation is compared with an existing adaptive inverse compensation method to demonstrate the improvement that the newly developed compensation method offers in minimizing actuator delay. The proposed improved adaptive inverse compensation method is demonstrated to further improve actuator control by reducing not only actuator tracking errors but also associated energy errors.