Global Sensitivity Analysis Of Prestressed Hollow Slab Girder Bridge And Reliability Calculation Based On Copula

With the rapid development of bridge construction in recent years,there are many highway bridges in operation,about 85% of which are medium and small span bridges.However,with the increase of the number of bridges in service and the increase of service time,the problem of bridge diseases has become increasingly prominent,and safety accidents have occurred frequently.Therefore,we should pay attention to the safety operation of small and medium-sized highway bridges.In this paper,a small and medium span continuous girder bridge in Wuhan is taken as an example.First,sensitivity analysis is carried out based on finite element model.Eleven influencing factors are selected from three aspects: structural material performance,restraint strength and load effects.Three evaluation indexes are established from the perspective of bridge bearing capacity.The sensitivity of influencing factors is roughly analyzed by scatter plot and Pearson correlation coefficient.Considering that scatter plot is not quantitative,Pearson coefficient is not applicable to non-linear model and the interaction between factors is not considered,the Extended Fourier Sensitivity Test(EFAST)is used to carry out global sensitivity analysis.The first-order and higher-order quantitative sensitivity indexes based on variance are given,and the factors of each evaluation index are ranked.From this,we can get the factors that need to be paid attention to in bridge safety analysis and safe operation,and factors that can be neglected to simplify calculation.In order to reduce the computational cost of EFAST method,the Least Squares Support Vector Machine(LSSVM)is introduced to construct the proxy model.Finally,by using the results of global sensitivity analysis,the factors with large influence are selected to calculate system reliability.The Copula theory is introduced to measure the correlation of failure modes in the system,and the failure probability calculation formulas of various series-parallel systems are derived.The ability to construct joint probability distribution by using Copula function transforms the traditional boundary estimation of the series-parallel model into point estimation,so as to obtain the specific failure probability value after considering the correlation.This method is applied to the calculation of system reliability of the continuous beam bridge mentioned above,and several calculation models are compared according to the degree of correlation consideration.In addition,the proposed method is verified by a truss structure in comparison with the existing theoretical values.In this paper,because the global sensitivity analysis takes into account the probability distribution characteristics of variables,the non-linearity of the model and the interaction between variables,more accurate sensitivity quantitative indicators can be obtained.The assessment of safe operation of bridges can be done based on these indicators.The proposed method of system reliability based on Copula doesn’t be confined to calculate the distribution characteristics of parameters and has high calculation accuracy.The application to continuous girder bridges in this paper shows that the failure probability will be severely smaller without considering the correlation of failure modes,which will lead to potential safety hazards.Therefore,it is very important to consider the correlation in system reliability calculation.