Stability analysis of SDOF real-time hybrid testing systems with explicit integration algorithms and actuator delay

Real-time hybrid testing is a method that combines experimental substructure(s) representing component(s) of a structure with a numerical model of the remaining part of the structure. These substructures are combined with the integration algorithm for the test and the servo-hydraulic actuator to form the real-time hybrid testing system. The inherent dynamics of the servo-hydraulic actuator used in real-time hybrid testing will give rise to a time delay, which may result in a degradation of accuracy of the test, and possibly render the system to become unstable. To acquire a better understanding of the stability of a real-time hybrid test with actuator delay, a stability analysis procedure for single-degree-of-freedom structures is presented that includes both the actuator delay and an explicit integration algorithm. The actuator delay is modeled by a discrete transfer function and combined with a discrete transfer function representing the integration algorithm to form a closed-loop transfer function for the real-time hybrid testing system. The stability of the system is investigated by examining the poles of the closed-loop transfer function. The effect of actuator delay on the stability of a real-time hybrid test is shown to be dependent on the structural parameters as well as the form of the integration algorithm. The stability analysis results can have a significant difference compared with the solution from the delay differential equation, thereby illustrating the need to include the integration algorithm in the stability analysis of a real-time hybrid testing system. Copyright (C) 2007 John Wiley & Sons, Ltd.