Multi-span Continuous Beam Bridge Seismic Fragility Analysis Considering Spatial Variation Of Seismic Ground Motions

Continuous beam bridge is a type of bridge structure often used in highway and railway traffic.In recent years,the span of continuous beam Bridges keeps increasing,which leads to the spatial variation effect of ground motion becoming an important factor in the seismic performance evaluation of Bridges.Based on this,the seismic vulnerability of multi-span continuous beam Bridges is analyzed in this paper.The seismic vulnerability curve under the action of spatial variation ground motion is obtained,and compared with the vulnerability curve under consistent seismic excitation,The effect of spatial variation of ground motion on the vulnerability of continuous beam Bridges is studied.First,a finite element model of a Multi-span continuous beam bridge is established by using Opensees software.The total length of the bridge is 636 meters.At the same time,the dynamic characteristics of the structure are analyzed.After that,taking the peak acceleration of ground motion as the seismic intensity index,based on the evolutionary power spectral density model of nonstationary ground motion,the spectral representation method was used to simulate two types ground motion samples at different intensities,which were uniform seismic excitation and the spatial variation of ground motion excitation,Twenty sets of each.And baseline adjustments are made to all seismic sample schedules.After that,the ground motions are loaded into the finite element model of the bridge for nonlinear time history analysis,and each of the two seismic excitation types was calculated to get the response.The displacement of pier top,bending moment of pier bottom,shear force of pier bottom and axial force of main beam are extracted in the analysis response,the effect of spatial variation of ground motion on structural response is analyzed.Finally,the fragility curves of the continuous beam bridge under uniform excitation and ground motion space variation were obtained.According to the results of seismic fragility analysis,the seismic safety of the structure was evaluated,and the influence of the spatial variation of seismic ground motions effect on the fragility of the continuous beam bridge was specified.The relationship between the uniform excitation and the peak acceleration of the spatially varying ground motion in a continuous beam bridge with the same damage degree is established.This paper provides a reference for further research on the influence mechanism of spatial variation effect of ground motion on seismic vulnerability of long-span Bridges,and also provides technical support for seismic design of multi-span continuous beam Bridges.