Research On Collapse Mechanism Of Xiaoyudong Bridge In Earthquake

Firstly, based on the damage analysis and site fault investigation of Xiaoyudong Bridge, this research speculated and analyzed the collapse process of the bridge collapsed in Wenchuan earthquake.And it made a clear judgment to the collapse process of the bridge.Secondly, shear and flexural strength of vulnerable component such as arch legs and bracing etc in Xiaoyudong Bridge were calculated by using Modified Compression Field Theory and UCFyber Software separately. Axial- shear mechanism and axial- flexural mechanism is considered in this calculation.Due to the lack of ground motion records close to Xiaoyudong Bridge, this research selected five ground motion records from Seismic database of Pacific Earthquake Engineering Research Center, which are similar to Xiaoyudong bridge with respect to the site conditions, similar magnitude and epicenter distance.And those original ground motion records were modified by using wavelet transform in order to generate artificial accelerograms compatible with the design spectrum prescribed in 2008 Seismic Code.Thirdly, finite element model of Xiaoyudong Bridge was established. And the performance of the structure was tested by using response spectrum of E1 performance level.And it was found no flexure failure or shear failure. In addition,nonlinear time history analysis on the structure was conducted by using the artificial accelerograms compatibled with response spectrum of E2 performance level. And it was found that some vulnerable components such as the bottom of arch legs.the bottom of the bracing and the mid-span of arch suffered flexure failure, and only the latter suffered shear yield because that the axial tension was so strong to lead the great reduction of the shear strength.By observing and analyzing the failure condition under nonlinear time history analysis of plastic hinge in vulnerable components, the damage of this structure in earthquake was assessed.Finally.based on actual seismic damage of Xiaoyudong Bridge.nonlinear time history analysis and longitudinal Pushover analysis was conducted to the structure on possible failure modes in order to study the failure process and mechanism of the plastic hinge of each vulnerable component. It was found that with the increase of longitudinal displacement, component yield firstly happened to bracing,and it was flexure yield under tension.then the bottom of arch legs in the same side reach yield situation, with the stress redistributed in the structure and the structure damaged seriously.