On the Fatigue Strength of Wires in Spiral Ropes

Spiral ropes of high load-bearing capacity are usually made of cold-drawn steel wires of high tensile strength. This material has been investigated by many researchers, not only to determine the mechanical properties of cold-drawn wires, but also to find out more about their stress-strain behavior under tensile loading and local three-dimensional stresses. It is now possible to determine load ranges for fatigue as a function of: surface conditions of the wire; the length of the wire; the diameter of the wire; local stresses resulting from damage to the wire surface; local stresses resulting from transverse pressure at points of contact where wires cross; friction between the wires produced by changes in stress; friction between the wires produced by changes in cable curvature; friction between wires and fittings or anchorage structures. Cables can be protected from corrosion due to environmental influences. If this is done the fatigue behavior of a twisted cable primarily depends on the addition of friction energy given to the material where strong contact forces cause three-dimensional stresses. A method of determining the fatigue strength of tension members made of cold-drawn wires is described using statistical methods, results of fatigue tests on short specimens, and precision measurements of the cold-drawn wire. It is possible to reach the material dependent fatigue limit of about 300 N/mm² with a spiral rope by a welldone structural design and corrosion protection.