Proceedings,
Characteristics of Locked Coil Strands Under Free Bending
(1994)
Abstract
In published literature, the strand constructions dealt with have
almost invariably involved only wires which are circular in crosssection.
There are, however, instances when shaped wires are
used in, for example, half lock and full lock coil constructions.
The three main shaped wires used in such constructions are the
wedge, half lock, and full lock "Z" or "S" shaped types.
In a recent series of publications by the author and his associates,
a theory backed by a number of large-scale and carefully
conducted experimental checks has been developed for predicting
the restrained bending fatigue life of axially preloaded spiral
strands at terminations. Traditional approaches invariably assume
that the maximum bending strains in the individual wires at the socalled
extreme fibre positions govern the strand's free bending
fatigue life. The newly developed (alternative) "contact stress-slip"
approach assumes (in line with laboratory and field observations),
however, the interwire fretting between often counterlaid wires in
various layers of steel cables to be the factor responsible for
individual wire· fractures.
It must be noted that there is currently a paucity of theoretical
and/or experimental results for locked coil steel cables. Only
recently, some large scale restrained bending fatigue test data
related to locked coil ropes has been published. It is by using this
data that it has been possible to propose a "contact stress-slip"
versus "fatigue life" curve for these cables which should be useful
as a predictive tool in design applications.
The paper outlines the salient features of the newly developed
approach as previously applied to spiral strands. This is then
followed by a detailed discussion of a broadly similar approach for
analysing restrained bending fatigue behaviour of locked coil
ropes, plus simple means of predicting their axial and plane-section
bending stiffnesses.
