Wire Ropes Under Bending and Tensile Stresses - Wire Ropes: Tension, Endurance, Reliability - page 278

3.4.1 Analysis of Rope Drives
3.4.1.1 Loading Sequence and Loading Elements
In the most rope drives, the wire rope is stressed by a number of bendings (e.g.
when running over several rope sheaves) and by changes of the tensile force as in a
loading sequence during a hoisting cycle, a working cycle or a trip. A hoisting
cycle is defined by an up and down movement. A working cycle is defined by a
rope movement forwards and backwards so that in the end the original condition at
the start of the working cycle is once again reached. A working cycle can result
from one hoisting cycle or, in the case of cranes, out of two hoisting cycles—one
with a load and one with no load going back to the starting position. A trip is
defined by a rope movement in one direction. Working cycles or hoisting cycles
are used especially for cranes and comparable lifting appliances. The rope
endurance in elevators, ropeways and mine hoistings is normally counted in trips.
The endurance calculation starts by establishing the loading sequence for the
wire rope zone (bending length) with the greatest stresses and separating this
loading sequence into loading elements. The symbols for the loading elements are
shown in Table 3.10 . The loading elements A, B, C and D are the standard loading
elements.
For wire ropes stressed by one of these standard elements, the rope endurance
can be calculated directly. The calculation method for elements A, B and D is
described in Sect. 3.4 . Element C which only has fluctuating tensile force is very
rarely found in rope drives and the rope endurance for this can be calculated
according to Sect. 2.6 . The three last loading elements in Table 3.10 , of which F
and G are very rare, can be converted into standard elements A, B, C and D.
Loading element E always occurs in rope drives with traction sheaves or in those
with drums if the load is changed while the rope is being wound onto the traction
sheave or the drum. In both cases, it is to be supposed that the whole bending take
place under the higher tensile force.
Normally the loading sequence during one working cycle (respectively during
one trip) is composed of the numbers of standard loading elements (bendings) per
loading sequence (working cycle or trip):
Simple bendings per working cycle
Reverse bendings per working cycle and
Combined fluctuating tensions and bendings per working cycle .
The symbols from Table 3.10 are used as an index to characterize the standard
loading element. The indices sim, rev, com and tens are suggested for the case that
the characterising symbols are not available for printing.
The bending length l is evaluated together with the numbers of the different
loading elements during one working cycle (trip). This wire rope bending length
represents the length of the wire rope zone which is stressed by the highest number
of loading elements (bendings). The bending length can be evaluated most simply
by marking off the distances a i from the end of the rope to the sheaves in both end