Reliability Analysis Of Cable-stayed Bridge System Under Natural Environment Corrosion

With the wide application of the cable-stayed bridges,more and more attention has been paid to the safety of the cable-stayed bridges.Damage or breakage accidents of bridge cables seriously threaten the normal operation of traffic routes and even the safety of people's lives and property.Therefore,it is great theoretical and practical significance to explore the degradation mechanism of cable,the mechanical properties after degradation,and the influence of cable damage on the reliability of cable-stayed bridge for the analysis of cable-stayed bridges service condition,the prediction of residual life,the maintenance and reinforcement of cable-stayed bridges and the safe operation and management of cable-stayed bridges.Firstly,this paper introduces the mechanism and corrosive model of each stage of cable corrosion degradation,and simulates the corrosion of different wires on the same cross-section according to the distribution law of corrosion between different wires.The ultimate bearing capacity of the corroded cables is obtained by fracture toughness method.The degradation of bearing capacity after corrosion and the load effects under gravity load,train load and wind load are considered,this paper use JC method to analyze the reliability of cable after corrosion.The results show that the reliability index of cable decreases with time.Under the combined action of environmental corrosion and fatigue stress,after 20 years of operation,the cable reliability index on both sides of caijia jialing river bridge is relatively low,reaching 3.975 at the minimum,only slightly higher than the national standard 3.7,which needs to be replaced in time.Secondly,the nonlinear cable load model is proposed to simulate the cable-breaking,and the dynamic analysis of the bridge after the cable-breaking is analyzed.The effects of the lasting period,the locations and numbers of the cable ruptures,bridge damping and the initial state of the bridge on the dynamic response of the bridge are also analyzed.The value of cable force near the broken cable was selected as the calculation parameter of DAF,and the reasonable value range of DAF was discussed.The results show that the dynamic amplification factor DAF₁,which is the ratio of relative dynamic effect to relative static effect before and after cable breakage,varies among 1.3 and 1.5.This implies the value of DAF₁ 2.0 suggested by PTI is conservative.In order to facilitate the design of bridge engineering,the DAF₂ is defined as the ratio of the dynamic response of broken cables to the static response of broken cables.The value of DAF₂ ranges from 1.1 to 1.3.Finally,the failure of the cable plays a controlling role in the failure of the cable-stayed bridges.In the analysis of reliability of the cable-stayed bridges,the influence of dynamic response caused by the failure of the cable is often neglected.In this paper,dynamic amplification factor DAF2 is used to approximate the dynamic response caused by cable fracture,and the reliability of cable-stayed Bridges under the action of corrosion and fatigue is compared from the aspects of cable bearing capacity and normal service limit state.The results show that analyzing the reliability of cable-stayed Bridges only from the number of cable breaks cannot reasonably evaluate the effect of cable breaks on the overall performance of Bridges,and may overestimate the risk of structural failure.In this paper,the influence of the corrosion degree of the cables on the reliability of the cables is considered,and the dynamic amplification factor DAF is introduced to analyze the dynamic influence of the cable failure on the reliability of the cable-stayed bridge system,so as to accurately evaluate the reliability of the cable-stayed bridge system under the corrosion of the natural environment.It is of practical significance to predict the remaining life of cable-stayed Bridges,repair and reinforcement,and safe operation and management.