Study On Seismic Fragility Of Continuous Girder Bridge Considering The Contribution Of Abutment Back Wall

Abutment is an important substructure in the bridge system.It supports and restricts the longitudinal displacement of the superstructure,and has a significant impact on the seismic response of the bridge.At present,most of the seismic design or research of bridges consider the abutment back wall as a sacrificial member or ignore the abutment back wall.It is considered that the main limiting factor of the longitudinal displacement of the abutment is the filling behind the abutment.However,the traditional method ignores the strength and stiffness of the abutment back wall,which may lead to the wrong evaluation of the seismic performance of the bridge.In view of this deficiency,this topic takes a 4 × Taking 30m continuous small box girder bridge as the engineering background,based on the fragility analysis method,this paper analyzes the influence of abutment back wall on the seismic performance of various components of continuous girder bridge,changes the abutment back wall parameters according to the actual engineering statistical results,and analyzes the influence of abutment back wall parameters on the seismic fragility of continuous girder bridge,so as to provide reference for later bridge seismic design.The main research contents are as follows:(1)Using OpenSees to establish the bridge nonlinear model considering the abutment back wall,select the appropriate seismic wave,input the longitudinal ground motion of the two bridge models,establish the seismic fragility curves of each component of the two bridge models,and compare and analyze the results.It is found that the damage exceedance probability of each component of the bridge is significantly reduced after considering the abutment back wall;With the increase of bridge damage degree,the influence of abutment back wall on the seismic fragility of bridge components increases gradually;Under all levels of bridge damage,the abutment back wall has the greatest impact on the seismic fragility of piers.(2)The design data of 50 continuous small box girder bridges in China are randomly counted,the abutment back wall parameters are changed according to the statistical results,and the influence of abutment back wall parameters on the fragility of bridge components is discussed.It is found that the thickness of the back wall and the loading height of the abutment have a great influence on the fragility of the continuous beam bridge,among which the thickness of the back wall has the most obvious influence,and the reinforcement of the abutment back wall has little influence on the fragility of the continuous beam bridge within the variation range.(3)In order to further study the influence of abutment back wall parameters on the seismic fragility of continuous beam bridges and change the pier height of the bridge,the same analysis method as above is adopted for continuous beam bridges with 10m,20m and 30m pier height respectively.It is found that the thickness of back wall and the loading height of abutment are still the two most significant parameters affecting the seismic performance of continuous beam bridge after the change of pier height;When the pier is up to 30m,the influence of abutment back wall reinforcement on the fragility of continuous beam bridge is gradually significant.Therefore,when the pier is high,the influence of abutment back wall reinforcement on the seismic performance of continuous beam bridge can not be ignored.