Mechanical Models of Helical Strands

Cables, ropes, and overhead electrical conductors are complex helical wire assemblies. Several analytical models are currently available for predicting their mechanical behavior or, at least, some technically interesting aspects of it. In these models, the underlying theory is generally based on a common elementary system, which can be termed a helical wire strand, generally consisting of a core surrounded by one or several wire layers. Depending on strand geometry, loading type (axial or bending), and also, on the required specifications (stiffness, strength, damping), a wide variety of hypotheses can be made. To address this problem, the following tentative classification is presented: fiber models, taking into account only axial wire forces; curved rod models, which include wire bending stiffness and in the most general case, twisting stiffness; and semi-continuous models, in which each wire layer is replaced with an equivalent elastic orthotropic medium. The different models are compared, together with the corresponding experimental data when available. The review is restricted to the elastic behavior under small deformations, which may include contact conditions, with or without friction, and possible stick-slip behavior. Studies related to more complex situations (multi-strand cables, contact with mechanical elements such as pulleys or clamps, viscoelasticity, fatigue, etc) are not included. This review article contains 107 references.