Bending fatigue life evaluation of bridge stay cables

Large amplitude cable vibrations are remarkably common on cable-stayed bridges, due to various aerodynamic loading mechanisms and/or motion of the cable ends. Geometric nonlinearity can be important in the dynamic behaviour and significant local bending stresses can arise at the anchorages, where rotation is restrained. This leads to a concern about the fatigue of these cables from the cyclic stress variations. This paper presents an analytical bending fatigue model for estimating the fatigue life of low-sag cables subjected to harmonic loading. Using this framework, the fatigue life of cables at the anchorage zone and guide deviator (if present) under external loading can be predicted. The results show that the use of a guide deviator can significantly extend the cable’s fatigue life at the anchorage. For cables with a guide deviator subject to severe loading conditions, the fatigue life is limited by the behaviour at the guide rather than the anchorage, which is consistent with previous observations. The fatigue life is greatly reduced if the cable jumps to a multi-modal dynamic response due to the cable nonlinearity. The single-mode zone where the dynamic response of the cable is always stable in a single mode, leading to a relatively long fatigue life, has been identified. Finally, the effect of cable inclination angle and ratio of cable weight to tension on the fatigue life has been analyzed.