Study On Reliability Evaluation Method Of The Damaged Cable In Service Environment

The service environment of cable-stayed bridge is complex,and it is exposed to the natural environment,especially in heavy acid rain area,serious air pollution area,water pollution area,marine climate ultraviolet radiation and so on,which is extremely vulnerable to environmental corrosion.For a long time,the cable structure continues to operate in the case of breakage,resulting in rust and fracture of steel wire or steel strand in the cable,which makes it premature to lose its function and has to be replaced.Therefore,it is very important to evaluate the safety and reliability of damaged cables.The research is supported by National Natural Science Foudation Item Study on prediction model of alternating load and erosion environment coupling cable corrosion fatigue mechanism and life(No.51478071)and Key project of Chongqing basic and frontier research project Corrosion fatigue damage mechanism and failure safety assessment method of cables under service environment(No.cstc2015jcyjBX0022)to research the evaluation method for safety and reliability of cable failure in service environment.The main research work and conclusions are as follows.Firstly,the evolution mechanism of steel wire corrosion is studied under the coupling effect of alternating stress and salt spray.An artificial accelerated test was carried out for two batches of 20 groups of galvanized steel wires under the coupling of salt fog environment and alternating load of 24 hours,120 hours,240 hours,480 hours and 840 hours.The weight loss of the steel wire was measured and the mechanical properties such as strength and elongation were tested.The tensile strength and elongation at the end of the zinc high strength steel wire decrease with the increase of the test time,and have a positive correlation with the weight loss,and the resistance reduction coefficient of high strength steel wire with different corrosion grades is obtained.Conclusion: the corrosion fatigue of the galvanized parallel steel wire is a corrosion factor from the damaged place to the corrosion steel.The surface corrosion pit of wire causes stress concentration,crack initiation and development,cyclic stress promotes the development of corrosion.Secondly,based on the stress intensity factor criterion,the fatigue crack propagation law of the single galvanized parallel steel wire under the interaction of alternating stress and salt fog environment is analyzed,and a mathematical model forthe resistance degradation of a single galvanized steel wire is established.Thirdly,on the basis of Fick’s law,the propagation law of corrosion factor in a section of galvanized parallel steel wire in a damaged cable is studied.It is found that the rate of fatigue corrosion is positively correlated with the concentration of corrosion factor,and a mathematical model of corrosion rate of galvanized parallel wire rope based on corrosion rate is established.Fourthly,according to the principle of linear elastic fracture mechanics and the mathematical model of corrosion of galvanized parallel wire rope,the ultimate stress of the limit stress C of any galvanized parallel steel wire at a certain time and the ultimate stress of the galvanized parallel wire rope at a certain time are derived.Finally,establish a time-dependent safety reliability evaluation model for cable breakage,modify the coefficient of variation in the random process of load using the periodic inspection results of the bridge,classify the cable damage according to the damage state of the cable,and correct the criticality of the resistance reduction coefficient and Daniel coefficient of different damage grade cables.Reliability index beta.Based on the engineering example,the safety reliability of cable damage in service environment and the safety and reliability of bridge breakage in service environment are evaluated.