The response of wire rope strands to axial tensile loads—Part II. Comparison of experimental results and theoretical predictions

Abstract

A set of carefully instrumented tests on straight single seven-wire steel strands with various end restraints and subjected to static axial loads are reported in Part I of this study [ Int. J. Mech. Sci. 29, 605–619 (1987)]. The strand extension in the free-end tests was up to 70% larger than that in the fixed-end tests and was larger for strands with lower helix angles. The torque generated in a fixed-end strand under load was greater for strands with a lower helix angle. Rotations in free-end tests were larger for strands with lower helix angles. Surface strains revealed uneven load sharing between nominally identical helical wires, with the largest strain deviations near the end grips of a strand. Repeated loading of the strands did not decrease the unevenness of this loading. Comparison between the computed predictions of this study and the previous theoretical predictions on the response of a single strand subjected to an axial load revealed that taking account of Poisson effects, friction and wire flattening at the contact surfaces has the effect of increasing extensions up to 2.3% with a negligible effect on the rotation. The theory predicts that slip does not occur between the core and helical wires in the strand lengths tested. However, it is concluded that plastic yielding at the contact surfaces causes migration of the effective line of contact. The computed predictions underestimated (0.4–7.3%) the extension of a fixed-end strand and overestimated (0.3–4.4%) the generated torque, while they overestimated the extension in the free-end tests by between 1.4 and 6.9%. The theoretical predictions overestimated strand rotation by between 9.0 and 15.7%. The low values of measured strand rotation can be accounted for, in part, by the effect of plastic yielding and flattening at contact on the rotation of the helical wires and migration of the effective line of contact between the core and helical wires.