of the numerical substructure, modeled in OpenSees [8]. The absolute displacement at the top of the numerical substructure is the target displacement, which is sent to OpenFresco [9, 10]. OpenFresco serves as the middleware which is used to interface the numerical substructure with the experimental superstructure through the control system. A predictor-corrector algorithm is then used to bridge the difference between the analysis time step size and the smaller control system time step size. The command displacement generated by the predictor-corrector algorithm is sent to the controller which controls the actuator driving the shake table. The resulting displacement of the table and the shear force under the physical specimen – recorded using loads under each of the isolators – are measured. The measured displacement is fed back into the controller and predictor-corrector algorithm while the measured shear force is fed into the numerical OpenSees model for the next analysis time step.