Time-dependent Reliability Analysis Of Bridge Structure Based On The Third-moment Method

Bridge as an important transportation hub,its reliability affects the operation of the whole society.In order to investigate the reliability of the bridge,calculating its reliability index is an useful evaluation method.However,a majority of the existing methods to calculate the bridge reliability index are the first order reliability method and response surface method.These methods all have the shortcomings of low precision or low efficiency.In order to enhance the calculation accuracy and efficiency of bridge reliability,this paper proposes the third-moment method to study the time-varying reliability of bridge.By summarizing the existing three third-moment methods and compiling the calculation program of the third-moment method,the time-varying reliability of two simply supported girder bridges are analyzed.The main works and contents of this paper are as follows:(1)The applications of second-moment method,response surface method and Monte-Carlo mehtod in the field of bridge reliability are systematically summarized.In addition,this paper makes a comprehensive summary of the research on the resistance and load effect that affect the reliability of bridges.(2)Based on the mid-span bending moment and the resistance,the limit state function is established.The time-varying reliability of a simply supported girder bridge is analyzed by using the third-moment method and the second-moment method.Considering two different resistance attenuation models,the time-varying reliability index and failure probability of the bridge are calculated respectively.(3)Considering the resistance decay and the non-stationary growth of vehicle load,the time-depedent reliability indices of the bridge in the next 60 years are calculated by different moment methods.Meanwhile,compared with the stationary load model,the sensitivity analysis is conducted.Considering the actual service situation of the bridge,the appropriate target reliability index is selected to predict the remaining service life of the bridge,and the prediction results of different moment methods are compared.According to the remaining service life,the safe driving threshold of the bridge is calculated.The threshold is compared with two different specifications,then the recommended value is given.(4)In order to consider the uncertainty and randomness of the traffic flow on the bridge,the proportion of time spent on the general operation and the intensive operation are both treated as random variables,and the influence of the random variables on the bridge failure probability is analyzed.In this paper,Monte-Carlo simulation(100,000 times)is adopted to verify the accuracy of different momet methods.The results show that the calculation error of the third-moment method is lower than the second-moment method,which indicates that the third-moment method is high-accuracy.(5)Taking a 13 m span bridge as an example,a time-varying reliability evaluation process of series system based on the third-moment method is established.The time-varying reliability indices of beams at different positions are calculated by different moment methods,and the failure probability of the bridge is fitted by Origin software.The results show that the time-varying failure probability meets the exponential function model.