Identification of system parameters of a large-scale dynamic multiaxial testing facility

Large-scale multiaxial testing facilities mainly serve to experimentally examine the horizontal behavior of full-scale critical structural members, such as columns and seismic isolation bearings, on which a large vertical compression load is exerted as they simultaneously undergo horizontal deformation. The system friction and inertia force play an important role in obtaining sufficiently reliable test results, and it is not easy to comprehensively grasp all the issues involved. To understand the system friction and inertia force of the Bi-Axial Dynamic Testing System (BATS) at the National Center for Research on Earthquake Engineering Tainan laboratory and to avoid complexity caused by specimens as much as possible, a lubricated flat sliding bearing is chosen as the specimen to be tested under horizontal triangular and sinusoidal reversed loading together with a constant vertical compression load. When no specimens are installed, that is, without vertical compression loading, the system friction of BATS generated by the various sliding surfaces can be identified and mathematically characterized using the horizontal triangular reversed loading test results; then, the effective mass of BATS can be estimated using the horizontal sinusoidal reversal loading test results to solve the inertia force problem. When applying a vertical compression load, it is assumed that the system friction of BATS and the shear force of the specimen are simply related to the applied total normal force (or vertical compression load) and horizontal excitation rate. An iteration methodology is proposed to identify and mathematically describe the dependency of the friction performance of BATS and the specimen on total normal forces (or vertical compression loads) and horizontal excitation rates by iterating the horizontal triangular and sinusoidal reversed loading test results. Finally, a lead-rubber bearing and a direct force measurement system are connected in series such that the measurement system precludes the system friction and inertia force and a series of tests are conducted. The reliability of the proposed mathematical model for BATS and the feasibility of the proposed direct force measurement strategy are further demonstrated by comparing the calibrated force response with the directly measured response.