Study On Seismic Vulnerability Of Rigid-continuous Girder Bridge Based On RBFNN

In the last decade or so,China has formed a high-speed railway network that runs from east to west and from north to south.The construction of railways is inseparable from the connection of bridges,especially in the western region where the terrain is complex and the slopes are steep.The special terrain determines that bridges are mostly high pier and large span structures,of which rigid-continuous girder bridges are the most common.With the increasing pier heights and spans,and the serious threat of widespread seismic zone distribution,the structural and operational safety of such high pier and large span bridges is facing serious challenges.Therefore,there is an urgent need to conduct research on the vulnerability of railway high pier and large span bridges.In this paper,a rigid-continuous girder bridge in northwest China is used as the engineering background,and the vulnerability analysis is carried out based on the response surface method and RBFNN(radial basis function neural network)using the finite element software CSI Bridge,with the following main research contents.(1)It summarises the status of relevant research at home and abroad,outlines the theoretical approach to the study of seismic vulnerability of bridges,and introduces in detail the basic principles of the response surface method,gives the calculation formulae of the vulnerability theory and the analysis process of the uniform design response surface method,thus laying the foundation for evaluating the seismic vulnerability of members or structures.(2)Taking a railway bridge in the northwest region as the research background,the finite element model of the whole bridge was established by using the finite element software CSIBridge,and the modal analysis was carried out by the Ritz vector method,and the dynamic characteristics of the whole bridge were given.On the basis of this,the material instantonal model was defined in conjunction with the specific structural configuration of the bridge,and the damage criterion of the bridge and the damage index of each member of the bridge structure were determined.(3)130 ground shaking records were selected from the Pacific Earthquake Research Centre(PEER)seismic database based on bridge site conditions and ground shaking characteristics.Of these,50 ground shaking records were used for finite element calculations.50 "structure-ground shaking" test sample pairs were obtained based on the homogeneous design method,and non-linear time course analysis was carried out to record the peak structural response.A probabilistic seismic demand model for each element of the bridge structure under ground shaking was developed using the response surface method,and the seismic susceptibility curves for each element of the bridge structure and the system were obtained and analysed.(4)The structural responses calculated by the finite element software were used as samples,of which 40 structural responses of ground shaking were used as training samples and the remaining ones as test samples.The appropriate ground shaking parameters were selected,and the MATLAB program was used as a platform to construct and train the RBFNN.and build a probabilistic seismic demand model,and finally plot the relevant seismic susceptibility curves for evaluation.(5)A comparison of the damage exceedance probability values for each element of the bridge structure obtained from the RBFNN predictions and the finite element calculations was carried out.The study shows that the damage susceptibility patterns of the two are basically the same,and the damage probability of each element of the bridge structure does not differ significantly.For pier 1,the maximum probability errors between the RBFNN predictions and the finite element calculations were 2.99%,2.43%,1.93% and 1.41% for the three different strengths(design,rare and very rare)of ground shaking,respectively,for minor,moderate,severe and complete damage.For the pier elements,the maximum probability errors of the two methods were 6.6%,3.96%,5.51%,and 1.64% for minor,moderate,severe,and complete damage states under three different intensities of ground shaking for the top of the most vulnerable pier #4,for example.Therefore,RBFNN has good generalization ability and can map the non-linear relationship between ground shaking and structural response better,and can be used for bridge seismic vulnerability analysis.(6)The fragility curves of bridge structural systems were obtained based on the first-order bounds estimation method.It is shown that the damage exceedance probability of the bridge system under all four damage states is higher than that of a single member,so it is too risky to assess the seismic performance of the bridge structure only by the vulnerability of each member of the bridge structure.Based on the interval variation of the seismic susceptibility curves,it can be seen that the difference between the upper and lower bounds of the bridge system exceedance probability increases and then decreases as the peak ground shaking acceleration PGA increases for each of the four damage states.The interval between the seismic susceptibility curves is smaller for minor and moderate damage,and larger for severe and complete damage.Therefore,it is reasonable to use the first-order bounds estimation method to assess the seismic susceptibility of this rigid-continuous girder bridge in both the slightly damaged and moderately damaged states.(7)The fragility of each member is compared.The study shows that: in the four damage states,with the increase of PGA,the probability of damage beyond the bearing is first higher than the abutment members and finally lower than the abutment members,the lower boundary of the system damage is first controlled by the bearing and then by the abutment members.4#pier damage beyond the probability are higher than the rest of the piers,in which,the damage beyond the probability of the top of the pier is higher than the bottom of the pier.The damage sequence of the piers is always 4# pier top,4# pier bottom,3# pier top,3# pier bottom,5#pier bottom,5# pier top.Support belongs to the fragile components,the main pier 4 # pier for the pier most fragile components,followed by 3 # pier,in the earthquake action of the above components have a higher probability of damage,should be paid attention to.