Design of steel cables against free-bending fatigue at terminations

The present paper highlights the significant shortcomings of the traditional maximum (extreme fibre) stress (or strain) approaches for design against free-bending fatigue at the fixed ends to axially preloaded steel spiral strands in various fields of application. The importance of catering for interwire/interlayer fretting in any realistic model for design against free-bending fatigue is emphasised. This is, then, followed by a brief review of the salient features of a promising theoretical model which takes interwire fretting into account. An extensive series of theoretical parametric studies, using a number of realistic spiral strand constructions covering a wide range of cable (and wire) diameters and lay angles, has been carried out in order to develop straightforward design formulations aimed at practising engineers. The possible practical limitations of the final results are briefly discussed. Moreover, a numerical example is presented to facilitate use of the proposed alternative design procedure. The present formulations are amenable to simple hand calculations.