Study On Seismic Vulnerability Of Continuous Rigid Frame Bridges With Double Thin-wall Piers

With the development of economy and society,the number of bridges in China has been very large.Recently,the continuous rigid frame bridges with double thin-wall piers have been widely used in China due to its advantages of large span capacity,construction easily,running smoothly and maintenance easily.The seismic performance of bridges designed and constructed in the early stage was poor due to the lack of seismic consideration.With the accumulation of people’s knowledge,the influence of earthquake was gradually considered in the process of bridge design.However,Chinese current codes for bridges’ seismic design and seismic response analysis were mainly compiled on the basis of bridge structures before 2010,which is probably ill-suited be applied to the recently commissioned or under construction long-span and complex bridges.Based on this,it is of great significance to study the seismic performance and seismic vulnerability for continuous rigid frame bridges with double thin-wall piers for ensuring smooth traffic network,emergency rescue and post-disaster reconstruction.The seismic vulnerability analysis of bridges aims to predict the damage degree of bridge structures under different earthquake intensities,which is expressed as the conditional probability that the structures or components exceed a certain failure state under the given seismic action.The seismic demand analysis of bridge members is an important part in the bridge vulnerability analysis.The seismic demand of bridge members is closely related to the characteristics of ground motion and the dynamic characteristics of bridge structure.It is of great significance to select a reasonable demand model by scientific seismic demand analysis method to research the seismic vulnerability of bridges.In view of the above analysis,the main research contents of this paper are as follows:(1)A typical continuous rigid frame bridge with double thin-wall piers was taken as the research object,and the nonlinear dynamic analysis model of the bridge was established by using the Open Sees program.Taking pier height parameters as control variables,the influence of pier height on the seismic response of continuous rigid frame bridges with double thin-wall piers was be studied and discussed.According to the bridge site,146 ground motion records were selected.By referring to existing studies,the engineering demand parameters of bridge components were selected and valued and each damage limit state is defined.(2)A method was proposed for seismic demand analysis of bridge members.This method is based on the basic idea of bidirectional matching and simultaneous optimization for engineering demand parameters and seismic intensity parameters,and uses mathematical statistics method to determine the optimal seismic demand model of each member,which is applicable to the analysis of seismic vulnerability curve and surface for bridges.This method was used to analyze the probabilistic seismic demand of the members for the continuous rigid frame bridge with double thin-wall piers and to determine the optimal seismic demand model of the bridge members.(3)Based on the optimal seismic demand models of each component,the seismic vulnerability of the continuous rigid frame bridge with double thin-wall piers was analyzed,and the seismic vulnerability of the bridge system was calculated based on the first-order boundary method.