Substructure Shake Table Testing with Force Controlled Actuators

Real-time hybrid simulation (RTHS) has emerged as a feasible and economical means for seismic performance assessment of structural systems. It has been successfully applied to study the system-level response, combining experimental and computational substructures. However, existing substructure techniques are limited to interface boundaries where the influence of unbalanced forces are not significant. Because existing formulation procedures and experimental loading are both displacement-based, unbalanced forces are inevitable in conventional RTHS. In some cases (e.g., testing of extremely rigid specimens, soil-structure boundaries), force equilibrium becomes more critical than displacement compatibility. To accommodate such conditions, a force-based approach is essential and has to be developed in RTHS. This study presents substructure shake table testing as a case study of force-based RTHS. A four-story shear structure is divided into two substructures. The first story is tested on a shake table while the rest of the structure is computationally simulated. The interaction between the experimental and computational substructures is addressed such that the measured acceleration at the top floor in the experimental substructure is used as the base input to the computational structure while computed base shear in the computational substructure is fed back to the experimental substructure through a force-controlled actuator. As such, the overall simulation is performed at real-time with force-controlled actuators. This study presents the underlying theories of the substructure shake table test method, centralized actuator control and preliminary numerical simulations.