Civil Engineering Reference
In-Depth Information
Fig. 3.62 Number of
bending cycles N A 10 of
Warrington or Filler rope
8 9 19 - FC - sZ as
function of the rope diameter
10 7
S=10kN
800 mm
D
630
d opt
10 6
D =
1250
500
1000
400
10 5
320
10 4
4
2
10 3
160
200
250mm
D = 125
S D1 (R o = 1770 N/mm 2 )
B A30min = 2
8 9 10
15
20
mm
30
40
50
5
6
7
rope diameter d
diameter is shown as a broken line. In reality, the optimal diameter is an economic
limit. If a rope diameter larger than the optimal one is used, the disadvantages are
that the rope endurance will be lower and the costs higher. The maximum of the
number of bending cycles is rather flat which means that there will only be a small
change in the number of bending cycles when a minor deviation from the optimal
rope diameter occurs. Therefore, the rope diameter can be smaller than the optimal
rope diameter with a reasonable percentage without too much of the rope endur-
ance being lost.
3.2.8 Ropes During Bendings
3.2.8.1 Residual Breaking Force
In the course of time, wire ropes running over sheaves will suffer from increasing
damage. Wire breaks and wear which occur reduce the residual breaking force of
the wire rope. Woernle ( 1929 ) systematically measured the breaking force of wire
ropes after different numbers of cycles in bending fatigue tests. His results are
drawn in Fig. 3.63 for a cross-lay rope in a series of test with three tensile forces. It
is to be seen that the reduction in the wire rope breaking force is weak at first and
then gets stronger towards the end of the rope's life. In many cases, the breaking
force even increases a little during the first third of the rope's life. As shown in
Fig. 3.63 , comparable results have been found by Davidson ( 1955 ), Arnold and
Hackenberg ( 1971 ) and Rossetti ( 1989 ).
Very high costs are involved in carrying out such research on residual breaking
forces as presented here. Many of the bending fatigue tests to find the course of the
residual breaking force have to be done for only one rope under only one loading.
 
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