Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 283

3.4.2 Tensile Rope Force

3.4.2.1 Simple Bending and Reverse Bending

When calculating the number of bending cycles, it is necessary to know the
effective rope tensile force as precisely as possible. If no more precise information
is available, the effective rope tensile force S for lifting appliance can be evaluated
from the load Q, the number of bearing wire ropes n T , the acceleration g due to
gravity and the global rope force factorsfs. For calculating the number of simple
bending cycles as well as the number of reverse bending cycles, the tensile force is

S ¼ Q g
n T

f S1 f S2 f S3 f S4 : ð 3 : 85 Þ

Table 3.12 lists the force factors f S1 - f S4 which increase the wire rope force.
The load guidance factorf S1 , the rope efficiency factor f S2 and the factor for parallel
arrangements of the wire ropes f S3 can be applied very simply and do not need any
further explanation. For two parallel ropes, the force factor f S3 has been estimated.
However, for several parallel ropes the factor f S3 comes from the measurements in
elevators of Janovsky ( 1985 ), Holeschak ( 1987 ) and Aberkrom ( 1989 ).
With force factor f S4 , the increase in the wire rope force due to the acceleration
of the load has been taken in account. Only in cases involving very high speeds, as
for example in special elevators, in ropeways and mine hoistings, a rope piece is
under acceleration or deceleration while passing more than one sheave.
Normally the bending length under acceleration or deceleration is very small.
To avoid too many positions in the Palmgren-Miner equation for all numbers of
bendings w (for any case if v B 1.0 m/s), the diminished force factor f S4w can be
used to replace the force factor f S4 . This diminished factor is

f S4w ¼ 1 þ w g ð f S4 1 Þ
w

: ð 3 : 86 Þ

In the approximating ( 3.86 ) w is the number of bendings and w g is the number
of bendings considered under acceleration. For hoisting cycles w g = 2 (with
w C 2) and for trips w g = 1.

3.4.2.2 Combined Fluctuating Tension and Bending

For combined fluctuating tension and bending, the equivalent tensile force S equ is