Hybrid simulation framework with mixed displacement and force control for fully compatible displacements

A novel framework for hybrid simulation of the seismic response of structures is presented that employs a mixed displacement and force control strategy. A key feature of this framework is a controller‐based displacement‐to‐force transformation that enables compatible displacements between the numerical and experimental model for force‐controlled degrees of freedom. The framework can be applied within conventional displacement‐based time‐integration algorithms allowing for implementation across a variety of software and hardware architectures; it is demonstrated here using OpenSees software with detailed nonlinear numerical models. This study includes numerical verification of the proposed force control strategy and actual implementation in a hybrid simulation of special moment frames with full‐scale beam‐column subassemblies. In the hybrid tests, the experimental column axial load is applied in force control due to the large stiffness and when combined with lateral seismic loads, results in column local buckling with significant axial shortening. The hybrid simulation results verify that the proposed mixed displacement and force control strategy effectively enforces displacement compatibility and force equilibrium between the numerical and experimental structures at the boundary degrees of freedom.