Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 276

The same number of hoisting cycles can be obtained with very different specific
tensile forces S/d 2 and diameter ratios D/d. As an example, Table 3.8a shows these
parameters for a row of numbers of hoisting cycles Z A10 (under full load) that with
a certainty of 95 % at most 10 % of the ropes have to be discarded. The data are
the same as in Table 3.8 , however with the more usual nominal rope strength
R 0 = 1.770 N/mm 2 and the drum and the sheave have the same diameter ratio.
In any case, non-rotating wire ropes have to be fastened freely rotating over a
swivel and other wire ropes have to be fastened to prevent any rotation.

3.4 General Calculation Method for Rope Drives

Rope drives should be dimensioned so that they comply with safety and economic
requirements. These requirements are listed in Table 3.9 as the five dimensioning
limits for rope drives.
The number of working cycles obtained by calculation agrees to a great extent
with the numbers reached by wire ropes in practical usage. The results of com-
parisons made between calculated and real wire rope endurance for a variety of
cranes, elevators, ropeways, mine hoistings, etc. correspond to a great extent,
Feyrer ( 1988 ), Beck and Briem ( 1993 , 1995 ), Verschoof ( 1993 ), Briem and Jo-
chem ( 1998 ) and Briem ( 2001 ). This method of calculation has been also used in
very special cases, such as computerised maintenance management by Wiek
( 1997 ) or for rope tension equalizer for floating drilling rigs by Bradon and
Chaplin ( 1997 ).

Table 3.9 The five dimensioning limits for rope drives, Feyrer ( 2007 )
Dimensioning Limit

1 Rope Working cycles

up to rope discarding or breakage (mean or 10% limit)

Requirement of the user

2 Donandt force

(yielding tensile force for a given bending diameter ratio
D/d)

S B S D1

The nominal tensile force S must be smaller than the
Donandt force that at most in 1 % of the ropes exceeds
yielding point

Strict limit

3 Rope safety factor

m = minimum breaking force F min / nominal rope tensile
force S. Ability to resist impact forces

m =F min /S C 2.5
For simple lifting appliance, more
for elevators, lifts etc.

4 Discarding number of wire breaks

(Detection to need rope replacement)

B A30 C 8
Recommendation for lifting
appliance

5 Optimal rope diameter d B d opt

Economic reasons