Sliding mode for equivalent force control in real-time substructure testing

The equivalent force control method uses feedback control to replace a mathematical iteration to solve the nonlinear difference equation in a real-time substructure test with an implicit integration method. The commonly used PID controller as a candidate of equivalent force control has only limited robustness for nonlinear systems. For real-time substructure testing with nonlinear specimens, the sliding mode control is proposed as the outer-loop controller of the equivalent force control. The design approach and implementation issues are discussed analytically. The effects of key parameters of sliding mode controller on the performance of equivalent force control are demonstrated through numerical simulation. The real-time as well as pseudodynamic substructure tests are carried out with a linear elastic spring and a nonlinear buckling restrained brace as experimental substructures. The effectiveness of the sliding mode control is verified by these tests. Copyright (c) 2014 John Wiley & Sons, Ltd.