Study On The Service Performance Of Stay Cable Under Corrosive Environment Conditions

With the advantages of large span,light weight and relatively simple construction operation,cable-stayed bridges have become one of the main bridge types for large span bridges.The stay cable is the main load-bearing member of the cable-stayed bridge,and ensuring the safety of its use is the basis for the normal operation of the whole bridge.In order to ensure the normal use of cable-stayed bridges,it is important to conduct the necessary research on the performance of cable-stayed structures.Based on the investigation of stay cable structure and a large number of literature,this paper studies the performance of stay cable structure.The main results are as follows:(1)The causes and mechanisms of cable damage are analyzed with respect to the structural characteristics of the cable.The outer sheath is broken leading to the exposure of the steel wire,and the corrosion caused by the reaction of moisture and other corrosive media in the external environment with the steel wire is the main reason for the corrosion damage of the cable.The corrosion of the steel wire includes four types of uniform corrosion,local corrosion,stress corrosion and corrosion fatigue.Among them,stress corrosion and corrosion fatigue caused more serious damage to the stay cable.The anodic dissolution theory suggests that the stress corrosion of cable wires is dominated by the oxidation reaction occurring at the anode.The theory of hydrogen cracking suggests that the reduction reaction at the cathode,i.e.,the process of gaining electrons from hydrogen ions,is dominant in the stress corrosion process.Corrosion fatigue is due to the action of alternating stresses and corrosive media,the iron base produces slip steps,so that the corrosion is intensified,the reverse slip is blocked,which in turn produces cracks.(2)ANSYS-Workbench software was used to simulate and analyze the single wire,including: uniform corrosion,etch pit depth,etch pit size change and the effect of etch pit spacing change on the mechanical properties of the wire.The results show that as the degree of uniform corrosion increases,the maximum equivalent force value at the bottom of the etch pit gradually increases.As localized corrosion proceeds,the depth of the etch pit increases,the value of the equivalent effect force at the bottom of the pit gradually increases,and corrosion increases.As the width-to-depth ratio of etch pits increases,the maximum equivalent force value at the bottom of the pit gradually decreases,when the pit width is infinite,can be transformed into a uniform corrosion situation.With the increase of the net distance between etch pits,the maximum equivalent force at the bottom of the etch pits gradually increases.At the same time,the maximum equivalent force value is smaller than the maximum equivalent force value of a single pit.This indicates that the presence of multiple pits at the same time will weaken the stress concentration effect.(3)A finite element model of the cable-stayed bridge was constructed based on Midas CIVIL software,and the overall analysis of the cable-stayed bridge was simulated.In the case of corrosion of all the bridge cables,the cable force of the stay cable will change,but the change is not significant.As corrosion reduces the effective cross-sectional area of the diagonal cable,resulting in an increase in the stress of the stay cable,and the greater the degree of corrosion,the greater the stress.When the corrosion rate is 25%,there is already part of the stay cable stress ratio exceeds the specification requirements,should be timely inspection,repair and reinforcement.Eight stay cables were selected to simulate the broken cable situation.When a breakage occurs,the force of several stay cables near the broken cable will change significantly.Some of the stay cables increase in cable force,while others decrease in force.The stay cable structure of the cable-stayed bridge undergoes a redistribution of the cable force.(4)A relatively complete evaluation system for the durability of stay cable structures was established.According to the damage mechanism of cable durability,a three-level durability evaluation index system of cable structure was established.A total of nine indicators were selected for the durability evaluation of the stay cable,including coating damage,sheath cracking,sheath breakage,wire damage,wire fracture,wire corrosion,anchorage damage,anchor head damage,and anchorage area damage.The weights determined by the IAHP and CRITIC methods were combined using the combined assignment method.A durability evaluation model based on the combined assignment method-TOPSIS theory was developed for the stay cable.The durability evaluation of 8 cables of a cable-stayed bridge was carried out with the example,and the evaluation results were in accordance with the actual situation.