Performance and Application of Equivalent Force Control Method for Real-Time Substructure Testing

AbstractThe equivalent force control (EFC) method has been developed for real-time substructure testing with implicit integration to replace the numerical iterative process with feedback control. This paper addresses two issues concerning the performance of this method. One is the determination of the force-displacement conversion factor (a key component of EFC) for nonlinear specimens. The analysis conducted here shows that the force-displacement conversion factor is largely governed by the properties of the numerical substructure and the numerical scheme when a small integration time interval is used. Otherwise, the factor has to be determined with the secant stiffness of the specimen and of the numerical substructure if a proportional-derivative controller is used for EFC. The other issue is the overshooting problem, which may arise for multidegree-of-freedom structures because of the relatively quick response feedback from the numerical substructure in the closed-loop EFC. This problem can be resolved by reducing either the EFC gains or the increment size of the equivalent force command. The analytical studies on these two issues are verified by numerical simulations and for real-time substructure tests conducted on structural models with buckling restrained braces. Furthermore, a real-time substructure test was conducted on an offshore platform with magnetorheological dampers in order to serve as an example of a practical application of the method.