Experimental Study On Long-term Performance Degradation Mechanism And Evaluation Model Of The Bridge Cable System In Service Environment

Cable-stayed bridge has the advantages of large crossing capacity,simple and beautiful shape,and has become one of the mainstream bridge types for highway and railway to cross rivers,lakes and seas,deep mountains and valleys.As one of the main load-bearing components of the bridge,the long-term performance of the cable system directly determines the operation safety of the bridge.The cable system is complex in structure,concentrated in force,difficult in sealing,weak in protection,and prone to corrosion fatigue damage under the coupling action of load and environment,which endangers the safety of bridge structure.In order to ensure the high quality construction and long life and safe service of cable bearing system Bridges,This paper is based on the National Natural Science Foundation project "Research on Corrosion Fatigue Damage Mechanism and Long-term Performance of Cable Anchoring System under Random Load and Environment Coupling Action"(No.52178273)and Chongqing Natural Science Foundation project "Research on Long-term Performance Decay Mechanism of Cable Anchoring System under Load and Electrochemical Corrosion Coupling Action"(No.cstc2021jcyj-msxm X1159).The mechanism and evaluation method of long-term performance degradation of cable-stayed cables were studied by conducting corrosion tests on cable of cable-stayed Bridges and dissecting tests on cable of real Bridges.The main research work and conclusions are as follows:(1)The typical diseases and causes of cable systems of 50 in-service cable-stayed Bridges are summarized and analyzed.The diseases affecting the safe service of cable systems mainly include: Corrosion,wire breakage and anchorage failure of cable body steel wire are mainly caused by aging and cracking of HDPE sheath and seal device,which leads to external corrosion factors entering the cable system.Coupled with the coupling effect of fatigue load on the cable,the cable system is corroded.The long-term performance index system of the cable system was established by the analytic hierarchy process.The key indexes that determine the long-term service safety of the cable system include the tensile strength of the wire,the corrosion fatigue property of the wire,the breaking force of the cable and the anchorage property of the cable.(2)An anatomical test was carried out on the cable removal system of in-service cable-stayed bridge.The macro and micrometer corrosion damage mode of corroded steel wire in anchorage section was analyzed by industrial microscope and digital micrometer,and the geometric dimension of corroded steel wire pit was analyzed statistically.The length,width and depth of the pit satisfy the skewed distribution.The macro and micro damage morphology and quality loss law of corroded steel wire with cable were revealed through accelerated corrosion tests.The mechanical properties of corroded steel wire were studied by tensile test and the degradation law of tensile strength of corroded steel wire was revealed.Furthermore,the environmental equivalent relationship between environmental corrosion and artificial accelerated corrosion of galvanized steel wire is established.When the galvanized steel wire is not completely corroded,the accelerated corrosion of dry-wet cycle in 1 cycle is equivalent to the effect of actual service environment in Guangzhou area for 1 year.(3)On the basis of the test results,the evolution of corrosion damage of corroded steel wire was simulated by cellular automata,and the corrosion damage evolution model of corroded steel wire was established by weight loss parameters.Furthermore,the corrosion damage evolution model of the cable body was established by combining the corrosion factor diffusion law and spatial damage distribution characteristics.(4)Combined with the corrosion damage evolution model of corroded steel wire and cable body,the long-term performance degradation model and bearing capacity evaluation method of cable were established.Based on the corrosion damage evolution model,the failure threshold of cable is proposed and the prediction method of cable remaining life is established.A solid finite element model was established to simulate the damage evolution and property degradation of steel wire with pitting,pitting and broken wire.