Application Of Copula Function And ANN Method In Seismic Fragility Analysis Of Extradosed Cable-Stayed Bridges

The extradosed cable-stayed bridge,which is a combined system bridge with complex mechanical properties and strong nonlinear behavior,is widely used because of its strong span capacity.Meanwhile,China is one of the earthquake-prone countries in the world.Therefore,it is urgent to research the extradosed cable-stayed bridge under earthquakes.In this thesis,a reinforced concrete extradosed cable-stayed bridge was used for studying its seismic fragility.The main contents are as follows:(1)The methods on seismic fragility of bridges and research status are summarized.Existing shortcomings of seismic fragility methods in the application of the extradosed cable-stayed bridge are discussed.The research methods and contents of this thesis are proposed.(2)A finite element model based on Opensees is established.Considering the flaws of traditional modeling methods,the file I/O function and the fast parametric modeling method are introduced to establish the finite element models of main beams and main towers.Based on the stress characteristics of the bridge,fiber elements are used to simulate the mechanical properties of transition piers and main piers.MIDAS/CIVIL finite element software is used to verify the dynamic analysis results of the model built by Opensees to ensure that the Opensees model is accurate and reliable.(3)El-Centro wave and nonlinear time-course analysis methods are used to calculate the response of the bridge under earthquakes.The effects of the peak stress and strain of concrete in different parts and the mechanical parameters of ordinary reinforcement on the bearing displacement,the curvature of transition pier bottom and main pier bottom under different PGA are investigated.(4)By using the experimental design method and combined with the above research results,the material parameters that have a great impact on the seismic response are selected to form the bridge ground motion sample group.In view of the shortcomings of traditional seismic fragility analysis methods,neural network metamodel is introduced to calculate and obtain the fragility curves of bearing,transition pier and main pier,which are compared with the fragility curves obtained by the traditional finite element method to evaluate the seismic performance of components.(5)Considering the correlation between the components in the system fragility,the Copula function is introduced to obtain the joint failure probability between the components,and the AIC criterion is used to select the optimal Copula function.Then system fragility curves based on the Copula function are completed which are compared with the first-order boundary method.The results show that the proposed method can obtain accurate system failure probability while considering the correlation of components,and it is a reliable fragility analysis method.