Wire Ropes Under Tensile Load - Wire Ropes: Tension, Endurance, Reliability - page 106

Fig. 2.20 Wire rope with
one strand layer

r w

r s

d

d s

The torque constant c 1 for a stranded rope with some round strand layers (strand
lay angle b j ) with fibre or steel core is
c 1 ¼ P j¼1 z j A j r Sj cos 2 b j sin b j þ P j¼0 z j A j d Sj c 1Sj cos 3 b j

d P j¼0 z j A j cos 3 b j

: ð 2 : 75 Þ

For a one-layer round strand rope with fibre core the equation for the torque
constant can be simplified enormously to

c 1 ¼ r S

tan b þ d S c 1S

:

d

The symbols here are the same as in Fig. 2.20 . For spiral round strand ropes
with the same strands in all strand layers the torque constant is a simplification of
( 2.75 )

c 1 ¼ P j¼1 z j

P j¼0 z j cos 2 b j cos 3 b j

r Sj sin b j þ c 1S d S

d P j¼0 z j

: ð 2 : 76 Þ

cos 3 b j

It is possible to calculate the torque of round strands and round strand ropes to a
satisfactory degree of accuracy with the equations presented here provided that
there is sufficient known geometric data for the rope. These methods of calculation
are of particular use to rope manufacturers when designing new ropes, especially
for so-called non-rotating ropes. Such ropes have to be designed in such a way that
the resulting rope torque is as close to zero as possible.
Calculating the rope torque with the equations presented here is only possible
for ropes which are not twisted. For twisted ropes, the torque is strongly influenced
by the torsional rope stiffness.