Three-Dimensional Seismic Vulnerability Analysis Of Railway Simply Supported Girder Bridge

The simply supported girder bridges are the main components of the railway bridge system in China because of its lower design cost,easy construction and maintaining convenience.Seismic vulnerability analysis is a significant technical method to evaluate the seismic performance and seismic damage of bridge structures.It is well known that the vertical component of the ground motion cannot be ignored,and the bridge structures are characterized by obvious spatial stress and deformation under the action of near-fault ground motion,therefore,the 3D seismic vulnerability under the near-fault earthquake action is systematically studied based on the typical three span simply girder bridges of the Sichuan-Tibet railway line.The main contents of the study can be summarized as follows:1.The detail introductions of the development course and research status of seismic vulnerability analysis of bridge have been provided;meanwhile,the deficiency of the present research is summarized.2.The curvature ductility ratio is selected as the damage index of the pier bending failure.The formula for calculating the nominal shear strength of bridge piers presented by Priestley(1996)is introduced and then section shear is chosen as the damage index of shearing failure of bridge pier;The damage index of the deformation failure of bearing is determined according to the design parameters of bridge bearings.3.The 3D finite element model of the example bridges is built by using the OpenSEES platform.The selection and inputting principle of the near ground motion are analyzed,and then 100 seismic records are chosen from the PEER database as an earthquake input sample.The seismic damage is simulated by the nonlinear time-history analysis method based on IDA.4.A method of 3D seismic vulnerability analysis for railway simply supported girder bridges is established by combining the reliability theory of engineering structure with the seismic vulnerability analysis.And based on the geometric meaning of the reliable index,the method is improved and optimized to solve the shortcoming that the calculation is not convergent,and the rate of convergence is slow.And then the paper compares the optimized method with the Monte Carlo method to verify the correctness and accuracy of the optimized method.5.The 3D seismic fragility analysis of railway regular and irregular simply supported girder bridges is carried out.The damage probability corresponding to different bridge structures in different seismic input angles is obtained.The most disadvantageous input range of ground motion for bending failure,shearing failure of pier and deformation failure of bearing are obtained.The 3D vulnerability of different components is compared and analyzed.It is concluded that bending failure is the main damage mode of pier,and bearing is the most vulnerable structure under the action of 3D near-fault seismic earthquake.