Prediction of the fatigue limit of stay cables
This paper deals with the prediction of the fatigue limit of stay cables undergoing bending deformations due to lateral vibrations induced by wind effects. Since the fatigue resistance of multi-layer spiral strands is related to the initiation of propagating fatigue cracks at the inter-wire contact sites in the external layers, the model presented is based on: (i) the determination of both the inter-wire friction loads and the bending stresses in relation with the bending deformation; and, (ii) the fretting fatigue limit of the wires as a function of the tangential friction force. The case of the bending fatigue loading close to the anchorage devices is addressed, including particularly the dynamic effects of articulated sockets through a modal analysis. For non lubricated and stabilised surface conditions, the fretting fatigue cracks are predicted to be initiated in the so-called partial slip regime i.e. before the gross slip initiation at the outer layer. The location in the strand and the calculated sensitivity to the extent of the amount of Likely fatigue crack initiation sites with the bending amplitude are also addressed. Finally practical considerations for actual service conditions are also discussed in relation with the theoretical predictions and its limitations.
Author: D. Siegert