Civil Engineering Reference
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higher endurance than ordinary ropes when running over sheaves. This is due to the
stress range for ordinary ropes on the bottom of the groove. Combined with the
pressure in the groove of steel or cast iron sheaves, this stress is the first cause of the
end of the rope's life. For lang lay ropes, the range stress in this position is so small
that the wires mostly break first in the inner rope due to high fluctuating stresses.
3.1.6 Force Between Rope and Sheave (Line Pressure)
Apart from all the stresses, wires in ropes are loaded by different pressures, both
within the rope as well as between the rope and the sheave. The pressure from the
force between the rope and the sheave groove varies along and across the sheave
groove. With line pressure, these pressures are considered as concentrated in one
line. The definition of line pressure (length related contact force) is contact force/
length of contact bow.
Measurements taken by Wiek ( 1982b ) and Molkow ( 1982 ) showed that the
pressure is much higher at the points where the wire rope meets the sheave than for
the remaining contact bow between. These pressure peaks at the contact points of
the wire rope and the sheave are caused by the bending stiffness of the wire rope.
These pressure peaks will therefore appear in all cases where a stiff tape or wire is
stretched over a sheave.
3.1.6.1 Line Pressure Between Tape and Sheave
Tape Force at the Contact Point
First of all, the calculation of the pressure between a tape and a sheave will be
presented to demonstrate the principle of what occurs as these calculations are
much less complicated than doing the same calculations for a wire rope, Feyrer
( 1986 ). Figure 3.13 shows a tape bent over a sheave and stretched by rope tensile
force S. The tape has a constant bending stiffness EJ, with E for the elasticity
module and J for the equatorial moment of inertia.
Fig. 3.13 Tape on sheave
Feyrer ( 1986a )
x
R -
x o
R o
ʔ x
ˑ
o
S
0
y
y o
S
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