平行钢丝束斜拉索的微动磨损分析

An Analysis on Fretting Wear of Stay Cable with Parallel Steel Wire Bundle

为了准确评估桥梁平行钢丝束斜拉索的耐久性,针对其在服役期间的微动磨损问题开展了研究。首先,根据平行钢丝索的索体结构分别计算了由扭绞角和护套紧箍效应造成的不同位置钢丝间的挤压力。其次,建立了平行钢丝间的接触力学模型,根据微动振幅和振动频率,提出了平行钢丝微动磨损深度的计算方法。最后,计算了某斜拉桥服役20 a的平行钢丝索的磨损深度,并与实测结果进行了对比分析。结果表明:接触力学模型能够较为准确地计算平行钢丝索不同位置钢丝在服役期的磨损深度;在拉索的长度方向,靠近端部钢丝的磨损程度要大于中部钢丝,从拉索的截面分布来看,外层钢丝磨损程度较轻,靠近圆心位置的钢丝磨损较为严重,理论计算结果与实桥旧索的检测结果基本相符;钢丝磨损深度的发展随时间的增加呈先快后慢的幂函数规律,磨损速率随着钢丝间的接触力、拉索的振动频率、振幅的增大而加快;算例中的钢丝镀锌层将在4.5~9 a内磨耗殆尽,远低于由环境腐蚀造成的镀锌层失效时间;微动磨损将使镀锌层过早失效,缩短了疲劳裂纹的萌生时间,如果不考虑平行钢丝间的微动磨损将使拉索寿命评估偏于不安全。

In order to accurately evaluate the durability of stay cables with 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 among the steel wires at different positions caused by the twisting angle and the sheath clamping effect are calculated separately.Then,a contact mechanics model among 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,wich 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 firstly fast and then slow with the increase of time,the wear rate increases with the increase of contact force among steel wires,vibration frequency and amplitude of cable;(4)the zinc coating of steel wire in the example will be worn out in 4.5-9 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.