SIMPLE FORMULAS FOR SPIRAL STRANDS AND MULTISTRAND ROPES

Steel cables are employed for many structural purposes, including stays for guyed masts and bridging applications such as hangers for suspension bridges and the main cables of cablestayed designs. In the offshore sector, they are, for example, used as moorings for guyed tower platforms. Traditionally, cable design and manufacture have often been considered to be as much an art as an exact science. The growing need for progressively larger diameter cables has necessitated a re-examination of the traditional methods of analysis and design, which are largely based on practical experience relating to significantly smaller diameter cables. In a series of recent publications, an analytical model, based on the treatment of the individual layers in spiral strands as orthotropic sheets, has been reported, whose predictions of various cable characteristics have been supported by carefully conducted and large-scale experimental data. The newly proposed model, however, employs rather complex mathematics: an extensive series of parametric studies on a variety of spiral strand constructions, with largely different wire diameters, lay angles and cable diameters, has led to the development of simple design office-type routines for everyday engineering applications, which form the subject of the present Paper. Based on these simple formulations, a method is also proposed for the more novel problem of multi-strand rope axial stiffness estimation, which varies as a function of axial load perturbation/mean ratio. The match between axial stiffness predictions on a 40 mm o.d. rope and available experimental data is encouraging. Numerical results for some realistic cable constructions are provided in order to facilitate the use of the proposed routines.