Wire Ropes Under Tensile Load - Wire Ropes: Tension, Endurance, Reliability - page 128

h 0 S ð x ¼ 500 Þ ¼ tan b h S ¼ 0 : 364

0 : 332 0 : 1019 ¼ 1 : 095 0 : 1019 ¼ 0 : 1116 m : tan b 00

The big increase of the lay length on the upper rope end can lead to a lasting
change of the rope structure. When a wire rope is let down, the lower rope end
should always be protected against turning. This rule has to be followed for wire
ropes with steel cores even if there are only small differences in height.

2.4.6 Wire Stresses Caused by Twisting the Rope

When twisting the wire rope, the wires will be stressed by torsion. Furthermore the
wires of the different wire layers and the strands of the different strand layers will
be elongated or shortened differently. However, these different elongations will be
prevented because the cross-sections of the strands and of the rope must remain
plane. Therefore a common elongation or shortening of the twisted strands or
ropes is forced by inducing longitudinal stresses in the wires and the strands.
The influence of the rope twisting on the rope stresses is so great that parts of
the rope can be broken far below the normal wire rope breaking force. For
example, in Fig. 2.25 the effect of the breakage of the rope core can be seen. For
an untwist angle x = -360 /100d of the rope, the rope core has been broken at
about 40 % of the normal rope breaking force. In the diagram the core breakage is
shown by an abrupt increase of the rope torque.
The derivation of the stress calculation is done again on the condition that the
wire ropes are of perfect geometry, that all wires are without self-contained
stresses and that each wire of the rope will be unstressed before and stressed from
the very beginning of the rope loading.

The sign definition:
rotary and twist angle is positive for turn off

negative for turn on (loosen)

longitudinal stress is positive for tensile stress

negative for compressive stress

2.4.6.1 Torsional Stress

When a round strand wire rope is twisted by rope twist angle x (+ for turn off), the
strand twist angle of the strand layer j is