Research On Anti-seismic Performance Of Bifurcated Continuous Box Girder Bridge

Nowadays,with the rapid development of urban economy,a relatively complete transportation network system has been formed in major cities,but due to the limited urban area and the impact of the road network and at the same time considering the visual beauty of the city,the emergence of urban overpass has become an inevitable trend.The most prominent feature of urban overpass in appearance is its high building height,the traffic connection between the two main lines can be realized by setting ramp bridges.A large number of data show that,when the earthquake comes,the bifurcation design of urban overpasses makes them have more complex stress characteristics,including torsion,distortion and shear lag,compared with curved bridges and skew bridges.As an key project of urban traffic,urban overpass will cause inestimable economic losses and even bring the whole city to a standstill once there are irreparable earthquake accidents such as pier damage,bearing falling off and beam falling under the earthquake action.So it is particularly important to study the seismic behavior of interchangeable continuous bridge.In this paper,a bifurcated continuous box girder bridge is taken as the engineering background.By analyzing the dynamic characteristics,response spectrum and nonlinear time history of the bridge,the bridge model is studied as follows:1)Firstly,this paper introduces the structure and stress characteristics of urban overpass,and compares and analyzes the research status of seismic resistance of urban bridges at home and abroad,and summarizes the seismic damage characteristics of urban bridges.2)Taking the engineering background of this paper as the research object,using the finite element analysis software SAP2000 to establish the bridge model,analyze the dynamic characteristics of the bridge model and understand the characteristics of the natural vibration of the bridge.3)Taking the bifurcation point of the bridge as the research parameters,respectively setting up bridge model of 10 °,30 °,45 ° and 60 °branch angle.And inputting seismic waves on two vertical directions in the plane by the 0 ° ~ 180 ° rotating excitation method,then respectively studying the worst earthquake input direction of each bridge and the worst bifurcation point of the bridge through the response spectrum analysis method.The results showed that the worse earthquake waves input angle of 10 ° bifurcate bridge are about 50 ° and 120 °;the worse earthquake waves input angle of 30 ° bifurcate bridge are about 40 ° and 140 °;the worse earthquake waves input angle of 45 ° bifurcate bridge are about 30 ° and 150 °;the worse earthquake waves input angle of 60 ° bifurcate bridge are about 20 ° and 140 °;And when the bifurcation angle of the bridge are about 45 ° and 30 °,the stress of the bridge is the most adverse.4)Taking the pier at the junction of the main line and the ramp bridge as the center,three kinds of seismic isolated bearing arrangements are designed.Based on the most unfavorable seismic input direction and the most unfavorable bifurcation angle determined in 3),this paper studies and discusses which type of seismic isolation bearing arrangement has the best seismic effect by using the nonlinear time history analysis.The results show that it is the most effective anti-seismic mode to install seismic isolation bearing on the middle pier and the transitional pier at the same time.5)Taking the 30 ° bifurcate bridge model as the research object,and arranging 1m long plastic hinge at the end of bridge pier,then using the nonlinear time history analysis method for ductile anti-seismic analysis,and comparing the results with the seismic isolated design results.For the bridge model in this paper,the results show that the seismic performance of the seismic isolation design is better than that of the ductile anti-seismic design,especially in the cross-bridge,its seismic advantages are more prominent.