Bridge Seismic Fragility Analysis Based On Improved Kriging Response Surface Method

With the continuous development of earthquake prevention and disaster reduction engineering projects around the world,seismic fragility analysis has also developed rapidly.Scholars in various countries used different fragility analysis methods to study the seismic performance of bridge structures.Particularly,the theoretical analysis method based on numerical simulation can be used to analyze fragility by establishing finite element numerical models,selecting appropriate seismic waves,defining damage indexs and damage limit states,which has become one of the most widely used and mature seismic fragility analysis methods.However,the previous seismic fragility analysis is mostly deterministic analysis,and now more and more scholars begin to consider the impact of the uncertainty of structural parameters on the seismic demand and capacity.Once the uncertainty of parameters is considered,a large number of real model calculations need to be carried out to analyze the seismic fragility of bridges by incremental dynamic analysis,which means the amount of calculation is very large.In this paper,the improved response surface method based on Kriging model is applied to the seismic fragility analysis of bridges.On the premise of ensuring the calculation accuracy,the amount of calculation of the real model is significantly reduced,and the calculation efficiency of fragility analysis is greatly improved.The research works in this dissertation are as follows:(1)The research background and significance of this paper are briefly introduced,and the research status of seismic fragility analysis and response surface method at home and abroad are summarized in detail.The main research and content of this paper are put forward.(2)The basic principles of nonlinear dynamic time-history analysis(NDTA)and incremental dynamic analysis(IDA)are described.By comparison,it is found that the IDA method does not need to assume that the exponential relationship between structural seismic demand and intensity of ground motion,and the calculation of IDA method is more real and accurate.The key problems such as the selection of seismic waves,the selection of random variables and the definition of the damage index and damage limit state are expounded.(3)The principles of different experimental design methods are described.By comparison,it is found that the sample points sampled by the number theory method are more uniform and stable.The construction principle of improved response surface method based on Kriging model is expounded,and the parameters of spatial function are optimized by genetic algorithm.Through numerical examples of reliability,it is proved that the accuracy of the response surface method based on Kriging model is higher than that of the traditional response surface when fitting the response surface with high nonlinearity.(4)The elastic-plastic finite element model of the cable-stayed bridge is established by using the Open SEES software with strong nonlinear analysis ability.The same bridge model is also established by using the general bridge finite element software Midas/Civil,to verify the accuracy of the finite element model.(5)The process of IDA fragility analysis based on improved Kriging response surface is described.The nonlinear curve fitting of the failure probability points of the members of main tower,piers and bearings in each damage limit state is carried out by using the least square method,and the accuracy of the fragility curve fitting is verified by the root mean square error(RMSE).According to the fragility analysis process of the example bridge,it can be concluded that the IDA analysis based on the improved Kriging response surface method significantly reduces the calculations of the real model and greatly improves the calculation efficiency of the fragility analysis compared with the traditional fragility analysis method based on MC or LHS sampling.