FREE BENDING OF SPIRAL STRANDS

For a given axial mean load, the response of a helical strand to an applied bending moment is considered. For the critical case near the terminations, the theoretical stiffness formulations describing the slippage between the layers in the strand have been derived in an analytical form, which is then used as an input to the differential equation describing the behavior of individual wires. The final results cast some light on an interesting phenomenon observed in previously reported bending fatigue experiments, where the first wire to fail was invariably the one that entered the socket on the bending neutral axis rather than (as might be expected) the wires in the extreme-fiber position. The theoretical results are of obvious value as an input to the interwire fretting fatigue analysis of strands. In particular, the paper should prove useful for the proper design and interpretation of the very expensive fatigue tests on large-diameter strands. © ASCE.