Multiaxial Real-Time Hybrid Simulation for Substructuring with Multiple Boundary Points

Real-time hybrid simulation (RTHS) results from the integration of numerical modeling with experimental testing of structural systems. In substructured RTHS tests, a reference structure may be partitioned into two or more substructures to save cost and space. Researchers may choose to model the elastic and less critical structural components numerically, while physically testing the components where appropriate numerical models are lacking. The dynamic characteristics of the numerical and physical substructures are combined by imposing the boundary conditions calculated from the numerical model in the physical substructure and returning measured physical forces back to the numerical model. To date, the majority of RTHS have been focused on substructuring with a single boundary point, physical substructure, and actuator. A multiaxial real-time hybrid simulation (maRTHS) framework was recently proposed, also using a single boundary point and physical substructure. However, for many practical engineering and research applications, more than one boundary point and physical substructure is necessary. Challenges to direct extension of the previously proposed maRTHS strategy to multiple boundary points include incorporation of a larger number of degrees of freedom in the physical experiment, robustness to coupling through the hybrid simulation when using multiple boundary points, and problems introduced by out-of-plane 3D motion. After presenting the analytical constructs of the proposed framework, these issues are explored, and a validation study is introduced involving a multispan curved bridge. This RTHS experiment employs two load and boundary condition boxes (LBCBs) with 12 actuators to assess the scalability of the proposed maRTHS framework to accommodate multiple LBCBs at multiple boundary points. Out-of-plane behaviors of this RTHS experiment are intrinsic. Further, both mechanical coupling present between the actuators for motions in Cartesian coordinates and the coupling introduced through the numerical structure in the RTHS are present. Nonetheless, the decoupled model-based control strategy performed well for both the linear and nonlinear structural responses. These results demonstrate the promising nature of the proposed maRTHS framework for investigating complex and nonlinear structural systems.