Time-varying Reliability Evaluation For Cables Of Cable-stayed Bridge Considering The Effect Of Environmental Corrosion And Measured Traffic Flow

Cable-stayed bridge is the first choice for long-span bridge because of its large span capacity and good mechanical performance.As an important force-bearing and force transfer component of cable-stayed bridge,cable is vulnerable to corrosion fatigue damage affected by random factors such as environmental corrosion and vehicle load during the design reference period of the bridge,causing the original 20-30 years Design life is often only 10-20 years.Replacing the cable will undoubtedly bring huge socio-economic losses,so it is of great engineering significance to study the reliability of cable-stayed cables during the design reference period.In this paper,the probability model of cable strength under the action of corrosion environment and measured traffic flow is studied,the cable resistance degradation under corrosion environment and measured traffic flow is evaluated,and the time-varying reliability of a long-span cable-stayed bridge is evaluated.The main research contents and results are as follows:1.The development of cable-stayed bridge and the main diseases faced by cable-stayed cable are expounded.The research status of corrosion fatigue and reliability analysis of cable-stayed bridge and the failure of cable caused by corrosion fatigue are summarized,which lays a foundation for further research.2.The strength degradation model of cable-stayed cables under corrosion fatigue damage is established.Based on the series-parallel model of cable-stayed cables,the steel wire elements are divided into steel wire elements,the effects of steel wire length,quantity and corrosion degree on the strength of cable-stayed cables are analyzed in turn,the strength coefficient function of the stay cable during its 25-year service life is fitted and used in the time-varying reliability analysis of the cables of a long-span cable-stayed bridge.According to the fitting results,the strength coefficients of cable-stayed cables under environmental corrosion during 5 years,10 years,15 years,20 years and 25 years of service are 0.9996,0.9777,0.8374,0.7110 and 0.5471,respectively.3.The fatigue damage of cable-stayed cables under the action of measured traffic flow is analyzed.Based on the dynamic weighing data of traffic flow in a expressway,the probability model of the characteristic parameters such as vehicle type,speed,weight and distance of the measured traffic flow is established.The Monte-Carlo method was used to simulate random traffic flow,and it was simulated for one hour in a way that loading on influence line.The fatigue damage of cable-stayed cable is analyzed based on S-N curve and linear cumulative damage criterion.It is estimated that the fatigue damage of stay cables under random traffic flow is considered to be 0.0007 after 25 years,and meet the service life requirements.4.The time-varying reliability of cables of a long-span cable-stayed bridge under corrosion and vehicle action is evaluated.First,the theory of structural reliability and its main calculation method are introduced,such as one-time second-order method,Monte Carlo sampling method,response surface method,etc;and then evaluates the reliability of typical cables of a long-span cable-stayed bridge by using the strength degradation model under corrosion fatigue damage of cable-stayed cables and the fatigue stress damage model of cables.The results show that in the 25 years of use,due to corrosion fatigue damage,the time-varying reliability index of stay cables decreases by 3.7-3.9,and the reliability index of the most dangerous cable after 25 years decreases to 1.8259.