Real time dynamic hybrid testing using shake tables and force-based substructuring

This paper presents the development and implementation of a novel structural testing method involving the combined use of shake tables, actuators and computational engines for the seismic simulation of structures. The structure to be simulated is divided into one or more experimental and computational substructures. The interface forces between the experimental and computational substructures are imposed by actuators and resulting displacements and velocities are fed back to the computational engine. The earthquake ground motion is applied to the experimental substructures by shake tables. The unique aspect of the above hybrid system is force-based substructuring. Since the shake tables induce inertia forces in the experimental substructures, the actuators have to be operated in dynamic force control as well, since either the force or the displacement, but not both can be controlled at a given point and at a given instant of time. The substructuring strategy and the numerical integration algorithms associated with the computational substructures are presented along with the implementation of the computational engine. A new dynamic force control strategy developed for this purpose using series elasticity and displacement compensation is briefly reviewed. Issues related to time-delay compensation are also discussed. Finally, an example of a real-time hybrid test implementation, and results from this experiment are presented. INTRODUCTION Simulation of structures under seismic loads is usually performed either experimentally or computationally. Experimental results are used to develop and calibrate computational models of structural components and assemblies. These computational models are used to predict the response of structures. Further experiments are then performed to validate and refine the computational models. Structural simulation is thus an iterative process involving alternate stages of experimentation and computation. This paper describes a new method of Real-time Dynamic Hybrid Testing (RTDHT) of structures which involves combined use of experimentation and computation and some of the above iteration can potentially be performed online. The new development was facilitated by 17 ANALYSIS AND COMPUTATION SPECIALTY CONFERENCE th Copyright ASCE 2006 17th Analysis and Computation Conference the new George E. Brown Network for Earthquake Engineering Simulation (NEES) deployment at University at Buffalo which provides unique opportunities for integrated experimentation and computing. Real time dynamic hybrid testing is a novel structural testing method involving the combined use of shake tables, actuators, and computational engines for the seismic simulation of structures. The structure to be simulated is divided into a physical substructure and one or more computational substructures. The interface forces between the physical and computational substructures are imposed by actuators and resulting displacements and velocities are fed back to the computational engine. The earthquake ground motion, or motion of other computational substructures, is applied to the experimental substructure by shake tables. A schematic of the RTDHT system is shown in Figure 1. The right side in Figure 1 shows the physical computational infrastructure including parallel operating computers required for the implementation of the forces and motions at the interface of the physical and computational substructures. The theoretical basis and the implementation of real time dynamic hybrid testing (RTDHT) is presented in the next sections. UNIFORM SUBSTRUCTURE STRATEGY IN HYBRID TESTING Substructuring using RTDHT required first modeling the entire structure and idealizing the interface conditions between the computational and the physical substructure. In this paper, a unified substrucutre technique for hybrid testing is derived for multistory models.