Multi-Axial Subassemblage Testing System for Hybrid Simulation With Large-Scale Structural Components

This article presents the Multi-Axial Subassemblage Testing facility of ETH Zurich, Switzerland (ETHZ-MAST) for quasi-static testing and hybrid simulation (HS) of large-scale structural components and assemblies. The ETHZ-MAST features a 6-degrees-of-freedom (DOFs, 3 translations and 3 rotations) loading system based on a steel crosshead and 10 hydraulic actuators. The control system of the test system allows for mixed-mode control of applied boundary conditions meaning that some DOFs can be controlled in force while the remaining are controlled in displacement. The control system relies on a kinematic model of the system and compensates for the elastic deformation of the crosshead and the backlash in the actuator clevises. The capabilities of the facility are demonstrated with two experimental campaigns on reinforced concrete shear walls, which comprise in-plane quasi-static cyclic testing and HS of nominally identical axially loaded specimens. One of the campaigns studied the transition between flexure and rocking behavior modes in specimens with spliced reinforcement, whereas the other addressed the transition between shear and sliding behavior modes. A comparison between the testing protocols revealed that the specimens tested in HS using a ground motion excitation had a larger displacement capacity than the nominally identical specimens tested using a quasi-static cycling test protocol. However, the behavior mode transitions the specimens exhibited did not depend on the test protocol, but on the specimen strengths and the applied axial loads.