Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 279

Table 3.10 The four standard loading elements

Other symbols
for the same
loading

Number of
bending or
load
cycles

Name Symbol

A Simple

bending

N sim

B Reverse

bending

N rev

Fluctuating
bending and
tension

C

N com

D Fluctuating

tension

N tens

positions, which can be easily obtained from CAD. As an example, the bending
length and the numbers of the loading elements (bendings) for a wire rope drive
with three sheaves is shown in Fig. 3.80 . For every sheave, the stroke is drawn as a
band beginning from both ends of the sheave contact bow. The reverse bendings
are marked by a thick line between the bands of both sheaves involved.
The rope length with the highest loading is the bending length l. The highest
loading represents the number of bendings with respect to the reverse bendings. In
the example Fig. 3.80 the small bending length is

l ¼ h ð u 1 þ a 2 þ u 2 Þ:

The loading sequence and the loading elements separated for this bending
length l in a cycle forwards and backwards are also drawn in Fig. 3.80 .
For the hoisting cycle of a crane, the loading sequence and the loading elements
of the wire rope can be seen in Fig. 3.81 . In this case, the stroke is so great that a
rope piece moves over both sheaves and the drum. At the start of the loading
sequence—lifting the load—the rope is exposed to increasing tensile force which is
again reduced at the end of the sequence—when the load is set down. To understand
the loading sequence, it is useful to start thinking from point P. The rope moves
with the double load-stroke 2h over the stationary sheave and the drum.