Research On The Corrosion-Fatigue Problems And Service Reliabilityof The Bridge Cables And Hangers

The suspension cables of suspension bridges,the stay cables of cable-stayed bridges and hangers of tied arch bridges may be fracture-critical members,and the reliability of these members would affect the safety of these complex bridges.Cables and hangers need to be replaced during the service life of bridges.Theoretically,thorough inspection and reliability evaluation of cables and hangers are needed to determine the timing of the replacement.While till now,there is no recognized criterion for the timing of the replacement of the cables and hangers.The suspension cables of suspension bridges,the stay cables of cable-stayed bridges,and hangers of tied arch bridges are vulnerable to deteriorate.The sudden broken of a cable or hanger may lead to catastrophic accidents,such as the Sichuan south gate of Yibin bridge and Fujian Wuyishan bridge,Xinjiang and Peacock River bridge.The collapse of a bridge is normally associated with fatal loss and severe social affect.The reliability of bridge cables and hangers has been a hot topic of the civil engineering,as it directly affects the reliability of the bridge system.Refined analysis and safety assessment methodology of cables and hangers should be developed,and efficient countermeasures have to be taken to enhance the safety of the complex bridges to ensure the safety of public.In addition to strengthening management measures such as design,construction,and maintenance,it is also one of the effective methods to timely grasp the dynamic reliability of cables and hangers and accurately assesses risks.This paper relies on the important scientific research instrument development project of the National Natural Science Foundation of China,"Development of structural fatigue experimental system in complex environment" No.11627802,and National Natural Science Foundation Project "Cable corrosion under the coupling action of alternating load and erosive environment" research on fatigue damage mechanism and life prediction model No.51478071,Key item of Chongqing Foundation and Frontier Research Program "Research on corrosion fatigue damage mechanism and damage safety reliability evaluation method of cable in service environment" No.Cstc2015 jcyj BX0022,Transportation "Research and development of reliability evaluation technology and key equipment for in-service reinforced concrete box arch bridges",Ministry of Transportation Science and Technology Project No.2014-318-223-030;Ministry of Communications,Road Science and Research Institute,Ministry of Finance;Basic scientific research business expenses project " highway mixing study on durability life design and index system of condensed bridges" No.2017-9035.The study is focused on the suspension cables of suspension bridges,stay cables of cable-stayed bridges,hangers of tied arch bridges,the three aspects of the reliability of cables and hangers service(safety,durability,and applicability)are the main lines,considering the possible causes of diseases in each component and the corrosion-fatigue problem of the cables and hangers in service,and combining with the service environment and test simulations,the reliability analysis model was established,and the reliability and safety risk assessment of cables and hangers service are analyzed and evaluated.In the light of accelerated corrosion test simulation,theoretical,finite element,origin numerical and gray-scale analysis of electronic scanning images to corrosion-fatigue damage mechanism are used after the failure of the protective system of cables and hangers,based on the on-site disease detection data,combined with the service environment,established a reliability model related lifting cables,the reliability analysis and evaluation of the safety risks for cables and hangers in service are carried out.The main research topics of this paper are as follows:(1)Through the analysis of the structure of the tension cables and the investigation data,it is found that the corrosion-fatigue of the cable body steel wire in the anchorage area is also one of the factors that affect the reliability.The accelerated corrosion test of simulated steel strand under the coupling action of acid rain environment and alternating stress reveals its corrosion fatigue characteristics.(2)The accelerated corrosion test of the simulated steel strand under the coupling of salt fog environment and alternating stress reveals the corrosion-fatigue mechanics mechanism of the cable body steel wire at the outer sheath breakage.(3)The accelerated corrosion test of simulated steel wire under the coupling of salt fog environment and alternating stress,the corrosion-fatigue damage evolution and breaking form of steel wire was analyzed,and the model was established,and the residual life of steel wire after corrosion fatigue was predicted in stages.(4)The whole cable system is designed into a series system composed of cable body steel wire,water accumulation in the lower anchorage zone and the cable body steel wire in the lower anchorage zone.The system carries out dynamic analysis and evaluation on the reliability of multi state service and safety risk of the cables and hangers system.The main innovations of the paper are as follows:(1)After the failure of the protective system,not only the corrosion-fatigue disease of the cable body steel wire in the outer sheath damaged,the water accumulated in the anchorage area,and the corrosion-fatigue damage of the cable body steel wire at this place also occurred.The corrosion-fatigue damage evolution mechanism of bridge sling under the coupling action of salt fog,acid rain environment and alternating load is revealed.(2)It is revealed that ductile brittle transition occurs after corrosion pitting develops into cracks after corrosion-fatigue.The corrosion-fatigue residual life prediction model of the three stages of steel wire corrosion and growth,crack nucleation and expansion,ductile brittle transition is established.(3)On the basis of the effect of different corrosive media,the gas corrosion-fatigue of the cable body steel wire at the damaged sheath of the outer sheath leads to the liquid corrosion-fatigue of the steel wire in the lower anchorage area,both of which have direct influence on the service reliability of the tension cables.A reliability and safety risk assessment method for service cables of service bridge based on series parallel system is proposed.