Seismic Fragility Analysis Of Suspension Bridges Considering The Input Direction Of Ground Motion

As a new type of bridge structure,suspension bridge has become a beautiful landscape in the city with its beautiful shape and outstanding landscape effect,and has been widely used in urban bridge construction in recent years.With the increase in the number of suspension bridges,its performance under earthquakes has received more and more attention.Therefore,it is important to evaluate the seismic performance of suspension bridges.At present,there are many studies on the seismic performance evaluation of suspension bridges,but most of the studies use the fixed value analysis method,and relatively fow studies use the probability method in seismic risk assessment.In this paper,a two-tower self-anchored suspension bridge is analyzed and studied,and the nonlinear time history analysis of the bridge is carried out with the help of finite element software Midas,and the time history analysis results under the seismic action of the bridge and the cross bridge are discussed respectively,which effectively reveals the vulnerability of the suspension bridge under the seismic action in different input directions,so as to provide an important reference basis for the design and construction of the suspension bridge.This article discusses the following:1.The finite element model of the suspension bridge was established,the appropriate ground motion record was selected,and the nonlinear time history analysis was carried out.According to the time history analysis results and damage indicators,the failure of each component in various limit states is obtained.2.Aiming at the differences in seismic vulnerability methods of suspension bridges,the advantages and limitations of the "cloud map method" and the "strip method" were compared and analyzed.At the same time,the influence of different ground motion strength indicators on seismic vulnerability is comprehensively studied from the perspective of efficiency and universality.3.Consider the influence of ground motion input direction on seismic vulnerability.According to the results of time history analysis,the structural response and ground motion parameters are regressed in logarithmic space,and the seismic vulnerability curve is established.The vulnerability curves of components and systems of suspension bridge structures under different ground input directions are compared,and the influence of ground motion input direction on vulnerability is analyzed.The results show that for the bridge in this case,the "cloud map method" is used as the vulnerability analysis method and PGA is selected as the ground motion strength index,which can obtain the best vulnerability calculation effect.Under the action of seismic along the bridge,the surpassing probability of each component of the bridge in various limit states is proportional to the ground motion strength,and the failure probability of each component is support,bridge tower and sling in descending order,and the failure probability of the structure as a whole is greater than the failure probability of individual components.Similarly,under the action of the cross bridge to earthquake,the calculation results are also in a positive proportional relationship,and the failure probability of each component is support,bridge tower and sling in descending order,and the failure probability of the structure as a whole is greater than the failure probability of each component.The vulnerability of the structure under the seismic action of the bridge is greater than that under the seismic action of the cross bridge.