The increasingly prominent durability problem of bridge cables not only leads to costly replacement but also causes safety concerns. This paper studies the time-varying reliability of corroded bridge cables through considering fuzzy failuare criterion. Firstly, the resistance degradation model of the corroded cable is established based on the corrosion rate of the steel wire and the corrosion propagation law of the cable section. Then, a time-varying reliability model of cable corrosion considering fuzzy failure criterion is proposed based on safety factor and the fuzziness of cable failure in operation period. A case study was carried out to compare the proposed model and the one with clear failure criterion with considering the time-varying reliability of service cable under different corrosion environment. The results show that the proposed model can reflect the variation of cable reliability in different corrosion environment and service time. Compared with the clear failure criterion, the gradual change rule of time-varying reliability index under the fuzzy failure criterion is better and is more consistent with the engineering practice. It avoids the difficulty in selecting the safety factor under the clear failure criterion at a certain degree. The time-varying reliability index of corroded cables has obvious time division, and it gradually decreases with the corrosion degree of steel wires. The service life of the cable with local sheath damage is only 8-10 years. Due to the irreversibility of steel wire corrosion, avoiding sheath damage and strengthening early flaw detection capability are the key to ensure the cable durability.

In order to accurately evaluate the durability stay cables of parallel steel wire bundle for bridges, the study is conducted on fretting wear during service. First, based on the structure of the parallel steel wire rope, the squeezing forces between the steel wires at different positions caused by the twisting angle and the sheath clamping effect are calculated separately. Then, a contact mechanics model between parallel steel wires is established, and a calculation method for the depth of fretting wear of parallel steel wires is proposed based on the amplitude and frequency of fretting. Finally, the wear depth of parallel steel wire cables in a cable-stayed bridge that has been in service for 20 a is calculated and compared with the measured results.The result shows that (1) the contact mechanics model can accurately calculate the wear depth of wires at different positions of parallel wire rope during service; (2) in the length direction of the cable, the wear degree of the steel wire near the end is greater than that of the middle steel wire, from the section distribution of the cable, the wear degree of the outer steel wire is light, the wear of the steel wire near the center of the circle is serious, and the theoretical calculation results are basically consistent with the detection results of the old cable of the real bridge; (3)the development of steel wire wear depth shows a power function rule of first fast and then slow with the increase of time, the wear rate increases with the increase of contact force between steel wires, vibration frequency and amplitude of cable; (4)the zinc coating of steel wire in the example will be worn out in 4.5 a to 9 a, which is far lower than the failure time of zinc coating caused by environmental corrosion. Fretting wear will lead to premature failure of zinc coating and shorten the initiation time of fatigue crack. If fretting wear between parallel steel wires is not considered, the life evaluation of cable will be unsafe.