Framework Development for Multi-Axial Real-Time Hybrid Simulation Testing

Abstract eng:
Real-time hybrid simulation is an efficient and cost-effective cyber-physical dynamic testing technique for performance evaluation of structural systems subjected to earthquake loading with rate-dependent behavior. A loading assembly with multiple actuators is required to impose realistic boundary conditions on physical specimens. However, such a testing system is expected to exhibit significant actuator dynamic coupling and suffer from potential time delays that are associated to servo-hydraulic system dynamics and control-structure interaction (CSI). One approach to reduce experimental errors considers a multi-input, multi-output (MIMO) approach to design controllers for accurate reference tracking and noise rejection. In this paper, a framework for multi-axial real-time hybrid simulation (maRTHS) testing is presented. The methodology consists in designing a cyber-physical system with multiple actuators with real-time control in Cartesian coordinates. For this matter, kinematic transformations between actuator space and Cartesian space are derived to control all six-degrees-of freedom of the moving platform in 3D Cartesian space. Then, a frequency domain identification technique with non-linear optimization tool is used to derive a model of the MIMO transfer function. Further, a Cartesian-domain model-based feedforward-feedback controller is implemented for delay compensation and to increase the robustness of the reference tracking for given model uncertainty. The framework is implemented using the 1/5th-scale Load and Boundary Condition Box (LBCB) located at the University of Illinois at Urbana-Champaign. To validate the proposed framework, a small scale structural systems with a physical cantilever rubber column specimen is considered. For real-time execution, the numerical substructure, kinematic transformations and controllers are implemented over an embedded system with a microcontroller and digital signal processor. Finally, the stability of the real-time system is demonstrated for an illustrative example of a single-degree-of-freedom structure subjected to earthquake loading. The test results shows that the framework can accurately provide excellent reference tracking performance.

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