Development of an Integrated Load Testing Device for a Substructure Hybrid Test of a Curved Bridge

A substructure hybrid test is an effective approach to reproduce the seismic behavior of engineering structures. The structure is partitioned into several substructures; those with complex behavior are analyzed experimentally, whereas the others are analyzed numerically, combining the merits of physical experiments and numerical simulations. Previous studies often loaded physical substructures in two or three translational directions. Simultaneous rotational loading in three Cartesian axes is difficult because the load testing device has to be configured spatially, resulting in control problems due to strong coupling. Special expertise in mechanical engineering is necessary to solve this problem. To this end, this study proposes an integrated load testing device suitable for physical loading in all six degrees-of-freedom simultaneously. The device is based on a Stewart platform and can provide a large axial force required by most gravity-bearing components. It also has a large inherent stiffness necessary to obtain the force-displacement curve from damage through complete failure. This paper describes the force-displacement mixed control based on the Stewart configuration, which is necessary for testing engineering structures. Control software is developed and interfaced with the mid-ware OpenFresco to coordinate the numerical substructure. A hybrid test is conducted using a small-scale, electronic-driven load testing device. The test ran smoothly without any malfunctions, demonstrating the excellent performance of the testing system.