Research On Seismic Vulnerability Of Continuous Girder Bridge Based On Multi-Dimensional Limit State Function

As the hub of traffic network,bridges play an irreplaceable role in post-earthquake relief work.Continuous beam-bridge occupies a large proportion in bridge structure because of its superior crossing capacity and good continuity.At present,the most commonly used method to study the seismic vulnerability of bridge structures is to establish the theoretical vulnerability curve.In the process of establishing the traditional theoretical vulnerability curve,the influence of the correlation between bridge components on the vulnerability of bridge system is not considered.Based on this,this paper considers that there may be linear correlation,nonlinear correlation,complete correlation and complete un-correlation among bridge components,and uses four multi-dimensional limit state functions to study the seismic vulnerability of continuous beam bridges.The main research contents are as follows:(1)This paper summarizes the theoretical methods of bridge seismic vulnerability at home and abroad,and introduces in detail the traditional methods of establishing the theoretical vulnerability curve.The bridge vulnerability analysis method based on multi-dimensional limit state function is introduced.It is found that: in the traditional method,the seismic vulnerability curve of bridge system is derived from the seismic vulnerability curve of components,and expressed in the form of interval;the seismic vulnerability analysis method based on multidimensional limit state function can directly obtain the accurate seismic vulnerability curve through the response of components.(2)In this paper,the continuous beam bridge with span of(65 + 40 + 40 + 65)m in Xining city is taken as the research background,the finite element model is established by using CSIbridge,and the dynamic characteristics of the continuous beam bridge are calculated.According to the damage criterion of bridge structure,the damage index of bridge component support and pier is determined.(3)Based on the site conditions of the continuous girder bridge and the spectrum characteristics of ground motion,the corresponding ground motion records are selected in the Pacific seismic research center database.The damage index of bridge components is quantified,and then the nonlinear time history analysis of the finite element model is carried out based on IDA method(incremental dynamic analysis method),and the probabilistic seismic demand model of bridge components under ground motion is established.(4)Based on the probabilistic seismic demand model,the seismic vulnerability curve of bridge components is established.The results show that: 51# fixed pier is more vulnerable than other piers.The vulnerability curves of 49# side pier bearing and 53# side pier bearing are similar,and the exceeding probability of damage is greater than other bearings.By comparing the vulnerability curves of pier and bearing under four damage states,it is found that the bearing is more vulnerable than the pier when the ground motion intensity PGA is the same.Therefore,it is necessary to improve the seismic performance of side pier support and fixed pier.(5)Based on the seismic vulnerability curve of components,the seismic vulnerability curve of bridge system is established by using the first-order boundary estimation method.It is found that the seismic vulnerability curve of bridge system is in the form of interval,and the interval is relatively large under the two damage states of severe damage and complete damage.Therefore,it is difficult to accurately evaluate the damage condition of bridge system by using the first-order boundary method.(6)Combined with the seismic response of bridge components,the multi-dimensional seismic vulnerability curve of bridge system is established by using four multi-dimensional limit state functions.The results show that: under the condition of a certain PGA,the multidimensional seismic vulnerability based on linear correlation function is the largest,the vulnerability based on circular function is the second,the vulnerability based on square function is the second,and the vulnerability based on concave function is the smallest.Among them,the seismic vulnerability curve based on linear correlation function is quite different from that based on concave function.(7)Considering the uncertainty of the correlation between bridge components,the equivalent seismic vulnerability curve of bridge system is established and compared with the seismic vulnerability curve of bridge system established by the first-order boundary estimation method.The results show that the equivalent seismic vulnerability curve can accurately describe the seismic performance of the continuous beam bridge.When the ground motion peak acceleration is small,the lower bound of the equivalent vulnerability curve is close to that of the first-order boundary estimation method.When the ground motion peak acceleration is large,the upper bound of the equivalent vulnerability curve is close to that of the first-order boundary estimation method.It shows that the correlation between the bearing and the pier changes with the change of the peak ground acceleration.When the peak ground acceleration is small,the correlation between the bearing and the pier is large.When the peak ground acceleration is large,the correlation between the bearing and the pier is small.