Study On Corrosion Fatigue Damage Mechanism And Long-Term Performance Of The Suspenders In Tied-Arch Bridge

In recent years,most of the suspenders of arch bridges in our country have had the problem of insufficient durability.The mechanical properties of the steel wires inside the suspenders deteriorate rapidly under the coupling effect of Corrosion fatigue,which seriously threatens the safety of arch bridges.At present,the research on the damage of suspension rods is not in-depth enough,and a practical and feasible evaluation theory and system have not been established to evaluate the remaining life of suspension rods.Therefore,this article is supported by the Chongqing Natural Science Foundation project "Research on the Long-term Performance Decay Mechanism of Cable Anchorage System under the Coupling of Load and Electrochemical Corrosion"(No.cstc2021 jcyj msxm X1159)and the Chongqing Yingcai Plan "Contract System" project "Research on the Long term Performance Accelerated Test Method of Bridge Beams under the Coupling of Load and Environment"(No.cstc2022 ycjh bgzxm0124),We have conducted research on the degradation of mechanical properties and residual fatigue life assessment methods for arch bridge suspension rods,providing a theoretical basis for the scientific evaluation of the long-term performance of arch bridge suspension rod systems.The main work and research conclusions of this article include:Firstly,the mechanism of corrosion damage,fatigue damage and Corrosion fatigue damage of arch bridge suspenders is analyzed,and the evolution law of suspender damage is studied.Secondly,artificial accelerated corrosion tests were conducted on the steel wires inside the dismantled suspension rods of an arch bridge that had been in service for 20 years,lasting for 0 days,7 days,14 days,and 21 days.The physical and mechanical properties of steel wires with different degrees of corrosion were compared and studied.The test results show that the apparent area of pit corrosion on the steel wire inside the removed suspension rod of an arch bridge after 20 years of service accounts for 58%,the mass loss rate is 2.39%,the elongation after fracture is 4.1%,the yield strength is1274 MPa,and the ultimate strength is 1561 MPa.After the artificially accelerated corrosion,the elongation of the steel wire after fracture is 2.8%～3.7%,and the proportion of the surface area of the steel wire pit corrosion is 63%,78%,and 86%,respectively.The mass loss rate is 5.22%,8.19%,and 9.80%,respectively.The yield strength is 1192 MPa,1134MPa,and 1053 MPa,and the ultimate strength is 1508 MPa,1432MPa,and 1396 MPa,respectively.Therefore,the corrosion of the steel wire inside the suspension rod has an undeniable impact on the mechanical properties and normal use function.Thirdly,fatigue loading tests were conducted on the steel wires inside the suspension rods with different degrees of corrosion,and the S-N curve and fatigue failure mode of the corroded steel wires were obtained.A prediction model for the remaining life of the corroded steel wires was established based on the two-parameter Weibull distribution model,and the number of cycles required for the steel wires inside the suspension rods with different degrees of corrosion to achieve different failure probabilities was studied,A residual fatigue life assessment method based on steel wire Pf-S-N curve clusters under different failure probabilities has been proposed,providing a reference for predicting the residual life of suspension rods in in-service arch bridges.The results show that as the degree of corrosion increases,the fatigue life of the steel wire significantly decreases,and the probability of brittle fracture of the steel wire is higher;The probability distribution of the fatigue life of steel wire conforms to the K-S Goodness of fit verification and can be expressed by a two-parameter Weibull distribution.Forthly,the spatial finite element model was used to simulate the spatial stress and deformation patterns of the arch bridge suspension rod,and the stress distribution and fatigue life of the corroded steel wire inside the suspension rod were studied;The stress distribution and fatigue life of corroded suspension rods in an arch bridge after 20 years of service were simulated using a solid finite element model of the suspension rods.The results show that the stress and stress increment increase with the expansion of corrosion pits,while the fatigue life decreases with the expansion of corrosion pits;The stress of the double pit model is 11% lower than that of the single pit model,and the multiple pit model will weaken the stress concentration effect.Finally,the long-term performance evaluation index system and evaluation method of the arch bridge suspender system are established.The key indicators of long-term performance include the ultimate strength of steel wire,the Corrosion fatigue performance of steel wire,the breaking force of the suspender,anchorage performance of the suspender.Based on the assessment model of the residual fatigue life of steel wires,a long-term performance evaluation method for arch bridge suspension rods was explored to provide technical support for ensuring bridge operation safety.