Design of sheathed spiral strands against free bending fatigue at terminations

Abstract

Significant shortcomings of the previously available approaches for designing steel cables against free beinding fatigue at nominally fixed terminations are briefly discussed. The salient features of a more appropriate design approach based on the ‘contact stress-slip’ parameter are presented. Unlike traditional approaches, this approach takes the effect of interwire/interlayer fretting fully into account. In view of the lengthy theoretical formulations for the previously reported contact stress-slip approach, the present paper covers in detail the development of a set of straightforward design formulations which are based on an extensive series of theoretical parametric studies. The parametric studies cover the full practical range of cable (and wire) diameters and lay angles in sealed spiral strands under external hydrostatic pressure due to depths of water, h, in the range 0 ≤ h ≤ 1500 m. The proposed design formulations are all amenable to hand calculations and should prove valuable to design engineers. A numerical example is provided to facilitate the use of the new design formulations.