Study On Seismic Damage Mechanism Of Thin-walled Hollow Square Bridge Piers

The seismic damage mechanism of high-pier rigid-frame concrete bridge is studied. The research focuses on the thin-walled square hollow pier, and stresses on the influence of higher vibration mode. In order to reproduce the nonlinear seismic response and damage developing progress of the entire bridge, the substructural online hybrid test is used. A new method to coordinate multiple physical regions is proposed, which employs the interface element.The main content of the paper are as follows:1. Finite element models was developed for the hollow square concrete pier. The analytical results was compared with and calibrated by the tested results. Parametric study was conducted using the axial force ratio and the aspect ratio as the primary parameters. It is found that a larger aspect ratio and a smaller axial force ratio are helpful to improve the ductility. A high axial force ratio is good at suppressing the cracks, but more vulnerable on fragile damage.2. Both pushover and time history analyses were conducted on the entire bridge. The reaction force of the substructure interface is obtained, which was used as the reference to design the specimens and the loading frame.3. A 1/12 scaled pier was tested quasi-statically. A more sophisticated loading pattern was considered, in which the boundary moment was also imposed on the specimen interface. To consider the contribution of higher vibration modes, two actuators were employed in the horizontal direction but at different height. Only one horizontal actuator at the top level is controlled by displacement, while the others controlled by force. The load pattern is determined through elastic simulation considering the first vibration mode. The test result is compared with previous test results not considering the boundary moment. It is found the new load pattern results in a lower seismic capacity of the specimen, but the damage progress is similar.4. To coordinate multiple subdomains with different physical properties, the interface element was proposed and modified to be applicable in the hybrid testing system. The theoretical basis was developed by the confined variational principle. The feasibility and accuracy were examined by numerical simulations.5. The static condensation technique and the BFGS method are further introduced into the interface element. Only boundary forces and displacement were implemented. Using this modified interface element, the nonlinear time history of a piece of plate was conducted.