Civil Engineering Reference
In-Depth Information
by winding the wire rope in the sheave or drum groove with side deflection or other
influences. For the lowest car position, the twist angle is given by ( 2.91b ) and for the
highest car position the twist angle is about zero. After passing a traction sheave, that
piece of rope is twisted in the opposite direction according ( 2.91a ) and this causes a
great range of stresses, as in the Oplatka and Roth ( 1996 ) tests described.
The real twist angles should be investigated under different influences by
computer simulation and measuring in installations. Furthermore a method should
be found by which the influence of fluctuating torsion and longitudinal stresses
from rope twisting can be introduced in the endurance calculation of wire ropes.
For installations not covering too great a height difference, wire ropes with fibre
core can be used as they have been up to now. Because of the great fluctuating
stresses especially in the steel core which even result in the total loosening of the
strands at the upper end of the rope, wire ropes with steel core in normal con-
struction with relative large torque should only be used to cover relatively small
differences in height. For installations with a very height difference rotation-
resistant ropes should be used.
However wire ropes with special steel core can be used for longer differences of
height, for that they are qualified by good experience or by calculated relative
small stresses.
2.5 Wire Rope Breaking Force
2.5.1 Measured Breaking Force
The breaking force F m of the wire ropes has of course to be evaluated by measuring
it. In the pieces of rope to be tested, it should be ensured that there are no visible
loose strands or wires. To compensate for any unavoidable minor loosening, the
rope length between the terminations should be at least longer than 30 times the
diameter of the rope. For the standard tension test, metal sockets are used as
terminations. If the wire rope breaks in or near a termination, the measured breaking
force of the wire rope may not be really obtained and the test should be repeated.
The tension test can of course be done with every kind of rope termination. But
the breaking force so determined is not the breaking force of the wire rope. It is
normally smaller. However, the tension test with resin sockets is an exception. In
most cases the breaking force with these resin sockets is a little higher than with
metal sockets and can therefore be taken too as the measured breaking force. But
normally the measured breaking force will be evaluated by the standard tension
test with metal sockets.
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