Lecture Slides
Chapter 17
Flexible Mechanical
Elements – Wire Rope
The McGraw-Hill Companies © 2012
Lecture Slides
Chapter 17
Wire Rope: 17-6
Expectation:
1. Design of a Wire Rope System
2. Application of Wire Rope
The McGraw-Hill Companies © 2012
Wire Rope - Chapter Outline (17-6 & 17-7)
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Section 17-6 Wire Rope Introduction Video
How Wire Ropes are Made
https://www.youtube.com/watch?v=eDVf71xd2cQ&featur
e=youtu.be
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Wire Rope: Typical Construction
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Types of Wire Rope: Regular Lay vs Lang Lay
Fig.17–19
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Wire Rope - Meaning of Lay
•The direction strands lay in the rope – right or left.
When you look down a rope, strands of a right lay rope go away
from you to the right. Left lay is the opposite.
(It doesn’t matter which direction you look).
•In regular lay, wires are laid in the strand opposite the direction
the strands lay in the rope
In lang lay, the wries are laid the same direction in the strand as
the strands lay in the rope.
•In appearance, wires in regular lay appear to run straight down
the length of the rope, and in lang lay, they appear to angle across
the rope.
•The length along the rope that a strand makes one complete
spiral around the rope core
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Wire Rope - Diagrams of several standard wire rope lays
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Wire Rope - Grades of Wire Rope
TS – Traction Steel
PS – Plow Steel
IPS – Improved Plow Steel (e.g.6 x 25)
EIPS or XIPS – Extra Improved Plow Steel
(15% improvement over IPS)
EEIPS or XXIPS – Extra Extra Improved
Plow Steel (10% Improvement EIPS)
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Sheave Design
Sheave Components
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Wire Rope - Elastic Limit (Video 3min)
Elastic Limit – The elastic limit or yield point of a material
Is the stress at which a material begins to deform plastically.
• Prior to the yield point, the material will deform elastically
and will return to its original shape when the applied stress
Is removed.
• Once the yield point is passed, some fraction of the
deformation will be permanent and non-reversible. For
rope or cable, this is the load that causes permanent set,
or deformation, of the strands.
• At the elastic limit the wire permanently stretches and
becomes thinner and thus weaker.
• A wire rope or cable must never be used at or near it’s
elastic limit even for a fraction of a second!!
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Wire Rope – Design and Construction
The types and size of wire used, the number of wires in the strands,
And the type of core determine the strength of a wire rope of a
Given size. A typical description of a wire rope would be:
1000 feet, ½” diameter, 6 x 25 filler, Preformed, Improved Plow Steel
Wire Rope, IWRC, Lang Lay
a. 1000 feet – length of wire rope is ordered or recorded in feet
b. ½” diameter – the nominal diameter of the rope
c. 6 x 25 Filler – the first numeral is the number of strands in the rope
(6) and the second is the number of wires in each strand (25). The
word Filler inidcates the pattern of the wires in the strand.
d. Preformed – a type of process assuring that each strand of the rope
is preformed to the helical shape it will assume in the finished rope.
e. IPS – signifies the grade of steel used in the wires
f. IWRC – indicates the type of core
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Wire Rope – Design and Construction (Preformed vs Non Preformed)
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Wire Rope – Rope Diameter (Correct vs Incorrect Method)
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Stress in Wire Rope
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Wire-Rope Data
Table 17–24
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Equivalent Bending Load

Wire rope tension giving the same tensile stress as the sheave
bending is called the equivalent bending load Fb
•Fatigue and Abrasion Resistance:
Fatigue – constant bending of the rope; smaller the wire
The more flexible the rope
Abrasion – Lang Lay ideal (e.g. Seale rope greater
resistance
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Percent Strength Loss
Fig.17–20
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Minimum Factors of Safety for Wire Rope
Table 17–25
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Minimum Factors of Safety for Wire Rope
Catalogue Breaking
Strength of the Rope
Factor of Safety =
Maximum Safe
Working Load
Max Safe
Catalogue Breaking
Working Load = Strength of the Rope
Factor of Safety
• Example – If the wire rope catalogue gives the breaking strength of the
rope as 10 tons, the max. safe working load is:
Max S.W.L. = 10 tons / 5 = 2 tons
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Minimum Factors of Safety for Wire Rope
Factor of safety accounts for:
•Reduced capacity of the rope below its stated breaking
strength due to wear, fatigue, corrosion, abuse, and
•Variations in size and quality
•End fittings and splices which are not as strong
•As the rope itself increases in line pull (load on the rope)
due to friction
•Of the rope passing over sheaves.
•Inaccuracies in the weight of the load
•Reduced strength of the rope due to bending over
•Sheaves.
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Wire Rope - Safe Working Loads (Practical)
Video – Incorrectly sized wire rope
Due to difficulty in remembering the SWL of the most
Common wire ropes, the following rule of thumb applies:
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Wire Rope – Catalogue Tables (Practical)
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Bearing Pressure of Wire Rope in Sheave Groove
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Maximum Allowable Bearing Pressures (in psi)
Table 17–26
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Relation Between Fatigue Life of Wire Rope and Sheave Pressure
Fig.17–21
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Relation Between Fatigue Life of Wire Rope and Sheave Pressure
Matching of Ropes and Sheaves
Effect of Improper Match between Rope and Sheave
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Fatigue of Wire Rope
Fig. 17–21does not preclude failure by fatigue or wear
 It does show long life if p/Su is less than 0.001.
 Substituting this ratio in Eq. (17–42),


Dividing both sides of Eq. (17–42) by Su and solving for F, gives
allowable fatigue tension,

Factor of safety for fatigue is
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Typical Strength of Individual Wires
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Service-Life Curve Based on Bending and Tensile Stresses
Fig.17–22
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Some Wire-Rope Properties
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Working Equations for Mine-Hoist Problem
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Working Equations for Mine-Hoist Problem
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Example 17–6
Fig.17–23
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Example 17–6
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Example 17–6
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Example 17–6
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Wire Rope: Group Exercise 17–29
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Solution Exercise 17–29
The objective of the problem is to explore factors
Of safety in wire rope. We will express strengths
As tensions.
Comments:
•There are a number of factors of safety used in
Wire rope analysis. They are different, with
Different meanings. There is no substitute for
•Knowing exactly which factor of safety is written
or spoken.
•In this problem, at the drum, we have a finite life.
•The remedy for fatigue is the use of smaller
Diameter ropes, with multiple ropes.
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Wire Rope: Solution Exercise 17–29 – (Table 17-24)
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Wire Rope: Solution Exercise 17–29 – Fig 17-20
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Wire Rope: Solution Exercise 17–29 – Figure 17-21
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Wire Rope: Solution Exercise 17–29 – Table 17-27
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Wire Rope: Solution Exercise 17–29
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Wire Rope: Solution Exercise 17–29
Using Table 17-24, Er = 12 x 106 psi and Table 17-27 dw =
0.067d and Am = 0.4 d2
At the drum (d=72”) Fb = 35.73 kip
At the sheaves (d = 36”) Fb = 71.47 kip
When calculating factors of safety involving bending we must
use the maximum bending force that the rope will experience,
so in this case that will be 71.47 kip.
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Wire Rope: Solution Exercise 17–29
b) Factors of Safety
Static with no bending:
s = Fu / Ft = 333/ 11.76
= 28.3
Static with bending:
ANS
s = (Fu – Fb)/ Ft
= (333 – 71.47) / 11.76
= 22.24
Fatigue without bending:
ANS
(Use a life cycle of 105 cycles)
p/Su for 105 cycles = 0.004
Ff = (p / Su) Su(wires) D d / 2
= 0.004 (240) 2 (36) / 2 = 34.56 (using sheave diameter = 36”)
f = Ff / Ft = 34.56 / 11.76 = 2.94
ANS
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Wire Rope: Solution Exercise 17–29
Fatigue with bending: (Calculate the FOS at the drum and at the
sheaves)
At the drum Fb = 35.73 kip and recalculating Ff at the drum gives
69.12 kip, therefore
f = Ff – Fb / Ft = 69.12-35.73 / 11.76 = 2.84 ANS
At the sheaves Fb = 71.47 and Ff = 34.56
f = 34.56 – 71.47 / 11.76 = -3.14
ANS
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Wire Rope: Solution Exercise 17–29
The negative number shows us that we have a serious
problem with fatigue life at the 3’ sheaves.
To remedy this we can increase the sheave size.
Another way to fix this issue would be to decrease the wire
size. To support the same size loads, we would have to use
multiple smaller diameter ropes to carry the weight.
*** Try using 1” rope, but use 3 ropes to support the load and
recalculate the static and fatigue factor of safeties. ***
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General Quiz – Whats Wrong with this Picture?
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General Quiz – Whats Wrong with this Picture?
1.Eye bolts are not properly seated.
2.Eye bolt orientation should be aligned to the hoist hook, not
broadside.
3.Hook loading of sling “legs” is less than 45deg. from horizontal,
resulting in tip loading. (Sling is rigged less than a 90 deg. full
included angle.)
4.There is a dual or compound load at the eye bolts created by the
sling’s leg and the horizontal portion. (Similar to the forces
experienced by a rigging block.)
5.An open basket hitch in this application can allow load running or
unrestricted movement. (Sling damage can occur, especially
friction/heat resulting in a melted sling and dropped load.)
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General Quiz – Whats Wrong with this Picture – Correct Setup
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