Wire Ropes, Elements and Definitions - Wire Ropes: Tension, Endurance, Reliability - page 44

F C is the calculated breaking force in kN obtained by calculation from the product
of the square of the nominal rope diameter d in mm, the rope grade R o in N/mm 2
and the nominal metallic cross-sectional area factor C

F c ¼ d 2

R o C
1000

: ð 1 : 6b Þ

The constants C, W and K are listed in Table 1.9 .
The wire rope tensile force S is very often related to the square of the nominal
diameter, to the so-called specific tensile force S/d 2 . The specific minimum
breaking forces F min /d 2 based on EN12 185 are listed in Table 1.10 for a simple
comparison of the tensile force and the minimum breaking force.
All the values for wire ropes with steel rope cores in Tables 1.9 and 1.10 are
given for IWRC. These values are also true for wire rope cores enveloped with
solid polymer ESWRC. For parallel-closed ropes (parallel steel core with outer
strands) PWRC the values are 6 % greater. Wire ropes with fibre-enveloped cores
EFWRC have values between those of fibre cores and steel cores, but these deviate
greatly.
Ratios of the measured and the nominal values evaluated on 49 parallel round
strand ropes are listed in Table 1.11 . This table shows that the mean measured
breaking force is 15.6 % greater than the minimum breaking force, Feyrer ( 1992 ).
This result is confirmed by the measurements made by Chaplin and Potts ( 1991 ).
They found that the measured breaking force is between 5 and 29 % greater than
the minimum breaking force. The factor K in the norm has apparently been
carefully chosen. Hankus ( 1983 ) and Apel ( 1986 ) have reported on the measure-
ments and calculations of the spinning loss factor.
Strand and wire forming. Normally, strands are either pre- or post-formed so
that they will retain their position in the rope structure when the wire rope is cut.
The grade of the strand forming is defined (proposal for the definition) by the
strand forming grade

U S ¼ d H d S ; m

d m d S ; m :

ð 1 : 6c Þ

Here d H is the outside diameter of the loose strand helix taken from the rope,
Fig. 1.37 ,d S,m is the measured strand diameter and d m is the measured rope
diameter. The wire forming grade is defined analogous to

Table 1.11 Ratio of measured and nominal values of parallel lay strand ropes, Fig. 1.37

Measured
Nominal

Deviation

Wire rope diameter d m /d 1.025 0.018

Metallic cross-section A m /A 1.049 0.049

Wire strength R m /R o 1.054 0.036

Rope breaking force F m /F min 1.156 0.054