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Proposed in this paper is an online hybrid test framework using a static and dynamic separated model scheme, where the equations of motion are solved by the operator-splitting (OS) algorithm, while the restoring force is obtained from a static analysis or quasi-static test of substructures. One of the keys of a successful substructure online hybrid test is the boundary coordination between the numerical and physical substructures. This is easily determined for the dynamic boundary whose displacement target is determined by the displacement predictor of the OS algorithm. However, the coordination is not straightforward for boundaries associated with static forces. This paper proposes an approximate method to determine the compatibility of the boundaries of static degrees of freedom, where the numerical substructure is analyzed first with the static boundary at the displacement of the previous step. The reaction force is then acquired from the analysis results as the target force of the corresponding degree of freedom of the physical substructure. The measured displacement is used as the target for the numerical substructure in the next step. In this procedure, the numerical substructure and the physical substructure alternatively move forward. Therefore, it is call staggered coordination. This is not a rigorous method to analyze boundary compatibility and equilibrium. However, it does make the substructure online hybrid test much easier and more feasible. Here, the staggered coordination scheme is examined by a six-story RC frame equipped with BRBs through both numerical simulation and physical testing. An energy-based index shows that the error introduced by this method can be ignored and that the proposed framework of online hybrid test works precisely without any malfunction.

Shaking table substructure testing takes the substructure with complex behavior physically tested, with the behavior of the rest structural system being numerically simulated. This substructure testing allows the payload of a shaking table being fully utilized in testing of the most concerned part, thus significantly increases its loading capacity. The key to achieve a successful shaking table substructure test is to coordinate among the substructures, specifically, to satisfy compatibility, equilibrium, and synchronization at the boundary between numerical and experimental substructures. A number of studies have focused on the essential techniques of shaking table substructure testing, and several applications have been carried out. Nonetheless, its progress is still in the preliminary stage, because of the limited applications using multi-directional shaking tables on large-scale specimens. This paper reviews a series of shaking table substructure tests and their associated implementation aspects including hybrid testing frameworks, time integration algorithms, delay compensation methods, shaking table and actuator control schemes and boundary force measurement methods. The key techniques required for a successful test are also stressed, such as the force control of actuators to coordination among the substructures. Finally, challenges for future studies and applications are identified and presented.

Wind turbines are being used in increasingly complex working environments that generate coupled wind and earthquake effects. Recent projects have tended to construct larger wind turbines to improve efficiency, but this generates more wind-induced vibration. Moreover, different threats are faced by a wind turbine at various stages. During construction, for example, vortex-induced resonance might result in a large lateral displacement of up to 1 metre, making the installation of blades difficult. Meanwhile, during service, the structure of a wind turbine can be damaged by strong gales and sometimes by earthquakes. The present study develops a tuned mass damper, which is designed to mitigate vortex-induced resonance. Shaking-table substructure hybrid tests are conducted to verify the performance of the tuned mass damper for different external loads. The experimental results confirm the effectiveness in terms of suppressing vortex-induced resonance, while the mitigation of the response to wind and earthquakes is limited.

Shaking table tests (STTs) provide an effective method to realistically assess seismic performance of nonstructural components (e.g., ceilings, water pipe supports and hangers, and glass screen walls), whose damage losses have been found to exceed those of structural components in recent earthquakes. During a shaking table test, nonstructural components respond upon the floor motion of a supporting frame where nonstructural components are attached to. Accurately reproducing floor response spectra of the supporting frame is therefore critical to achieve consistent and high-quality test results. This paper proposes a multi-directional decoupling iteration (MDI) control method to achieve this demand. The principle of the proposed MDI method is explained first. The effectiveness of the proposed controller to overcome the dynamic coupling between the supporting frame and the shaking table and to accurately reproduce floor response spectra along multi-directions is validated through a series of STTs of water pipe supports and hangers.