Effect of Belay Devices and Anchor Points on Dynamic Climbing Rope Strength

University of Strathclyde

MSc Individual Project

The Effect of Top Rope Setup onDynamic Climbing Rope Strength

Author:

Craig Millar

Supervisor:

Dr. Andrew McLaren

A thesis submitted in partial fulfilment for the requirement of degree in Master

of Science in Power Plant Engineering

August 20, 2012

Craig Millar 201087233

Copyright Declaration

This thesis is the result of the author’s original research. It has been composed by

the author and has not been previously submitted for examination which has led

to the award of a degree.

The copyright of this thesis belongs to the author under the terms of the United

Kingdom Copyright Acts as qualified by University of Strathclyde Regulation 3.50.

Due acknowledgement must always be made of the use of any material contained

in, or derived from, this thesis.

Signed: Craig Millar Date: August 20, 2012

1


Abstract

This project centres on the investigation of the effect of belay devices

and anchor points on the strength of dynamic climbing rope and also the

effect of use on the Black Diamond ATC belay device.

The use of a belay device reduces the strength of the rope by between

15% and 65% for new devices depending on the device. For used ATC

devices the strength lost is even higher, up to 73% of the straight rope

strength. There seems to be a correlation between the radius of curvature

the rope is forced round in the device and the maximum breaking load.

The changes between new and used Black Diamond ATC devices are

caused by the abrasion of the rope over the working surface. There is no

change in the internal crystal structure from the heat produced in use.

Despite minimal successful tests of the anchor point diameter there is

a clear trend that a decrease in diameter results in a decrease in overall

strength. A reduction in diameter of the anchor point from 56.6 mm to 11.1

mm results in a reduction of 20% in the rope strength.

There is also an interesting property of the rope where the stiffness re-

duces after a certain load is applied but more work will have to be done to

understand this.

2


Contents

List of Figures 5

List of Tables 6

1 Introduction 7

2 Equipment 9

2.1 DMM Aero HMS Carabiner/Belay Master . . . . . . . . . . . . . . 9

2.2 Black Diamond ATC . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3 Black Diamond ATC Sport . . . . . . . . . . . . . . . . . . . . . . . 10

2.4 Italian Hitch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.5 DMM Figure of 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.6 Anchor Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.7 Tinius Olsen Tensile Strength Testing Machine . . . . . . . . . . . . 13

2.7.1 Rope Clamps . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.7.2 Anchor Point . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.8 DMM Statement Dynamic Climbing Rope . . . . . . . . . . . . . . 15

3 Method 17

3.1 Straight Pull Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2 Belay Device Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.1 New Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.2 Worn Black Diamond ATC . . . . . . . . . . . . . . . . . . . 18

3.2.3 Microscopic Analysis . . . . . . . . . . . . . . . . . . . . . . 19

3.3 Anchor Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

4 Results and Analysis 20

4.1 Straight Pull Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.2 New Belay Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4.2.1 Black Diamond ATC . . . . . . . . . . . . . . . . . . . . . . 23

4.2.2 Black Diamond ATC Sport . . . . . . . . . . . . . . . . . . 27

4.2.3 Figure of 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

4.2.4 Italian Hitch . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

3


4.3 Worn ATC Device . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.3.1 Rope Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

4.3.2 Microscopic Analysis . . . . . . . . . . . . . . . . . . . . . . 35

4.4 Anchor Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.5 General Observations . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5 Conclusions 45

5.1 Belay Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

5.2 Anchor Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6 Further Work 50

7 Acknowledgements 51

References 52

A Table of Rope Info 53

B Tables of Test Data 56

B.1 Staight Pull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.2 Belay Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

B.3 Worn ATC Device . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

B.4 Anchor Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4


List of Figures

1 Diagram of a typical top rope setup. [Vogel(2002)] . . . . . . . . . . 7

2 Picture of DMM Aero HMS Carabiner . . . . . . . . . . . . . . . . 9

3 Picture of Black Diamond ATC set up . . . . . . . . . . . . . . . . 10

4 Picture of Black Diamond ATC Sport . . . . . . . . . . . . . . . . . 11

5 Picture of Italian Hitch set up . . . . . . . . . . . . . . . . . . . . . 11

6 Picture of DMM Figure of 8 set up . . . . . . . . . . . . . . . . . . 12

7 Picture of Anchor set up . . . . . . . . . . . . . . . . . . . . . . . . 13

8 Picture of Anchors used. a) 56 mm, b) 19.2 mm, c) 11.1 mm . . . . 13

9 Picture of Tinius Olsen Tensile Testing Machine . . . . . . . . . . . 14

10 Picture of a) Rope Attachment b) Anchor Attachment . . . . . . . 15

11 Picture of DMM Statement Dynamic Rope . . . . . . . . . . . . . . 16

12 Picture showing initial and final clamp position . . . . . . . . . . . 21

13 Plot of Load as a function of Extension for a straight rope . . . . . 22

14 Plot of Load as a function of Extension for the ATC 1 . . . . . . . 25

15 Plot of Load as a function of Extension for the ATC 2 . . . . . . . 26

16 Plot of Load as a function of Extension for ATC Sport. . . . . . . . 28

17 Plot of Load as a function of Extension for Figure of 8. . . . . . . . 30

18 Plot of Load as a function of Extension for Italian Hitch tests. . . . 32

19 Plot of Load as a function of Extension for Worn ATC . . . . . . . 34

20 Macro photos of New and Used ATC . . . . . . . . . . . . . . . . . 36

21 Micro Photos of Inside Edge of ATC Devices . . . . . . . . . . . . . 36

22 Micro photos of mid section of new and used ATC. . . . . . . . . . 37

23 Micro photos of large radius of new and used ATC . . . . . . . . . . 37

24 Micro photos of small radius of new and used ATC . . . . . . . . . 38

25 Macro photos of small radius of new and used ATC . . . . . . . . . 39

26 Plot of Load as a function of Extension for a 56.6 mm Eyelet. . . . 41

27 Plot of Load as a function of Extension for an 19.2 mm Shackle. . . 42

28 Plot of Load as a function of Extension for an 11.1 mm Shackle. . . 43

29 Comparison of Belay Devices . . . . . . . . . . . . . . . . . . . . . 47

30 Comparison of Braking Strength Against Anchor Point Diameter . . 49

5


List of Tables

1 Properties of DMM Statement Dynamic Climbing Rope . . . . . . . 16

2 Table of rope centre position . . . . . . . . . . . . . . . . . . . . . . 18

3 Worn Black Diamond ATC Belay Device Average Test Data . . . . 33

4 Single/Double Strand Comparison table . . . . . . . . . . . . . . . 39

5 Average Rope Strength for Varying Diameters of Anchor Point . . . 40

6 Table showing the Position of Change in Gradient . . . . . . . . . . 45

7 Summary of Belay Device Tests . . . . . . . . . . . . . . . . . . . . 46

8 Rope Description and Comments . . . . . . . . . . . . . . . . . . . 55

9 Straight Pull Test Data . . . . . . . . . . . . . . . . . . . . . . . . . 56

10 Black Diamond ATC Test Data . . . . . . . . . . . . . . . . . . . . 56

11 Black Diamond ATC Sport Test Data . . . . . . . . . . . . . . . . . 57

12 DMM Figure of 8 Test Data . . . . . . . . . . . . . . . . . . . . . . 57

13 Italian Hitch Test Data . . . . . . . . . . . . . . . . . . . . . . . . . 57

14 Worn Black Diamond ATC 1 Test Data . . . . . . . . . . . . . . . . 58



17 56.6 mm Eyelet Test Data . . . . . . . . . . . . . . . . . . . . . . . 59

18 19.2 mm Shackle Test Data . . . . . . . . . . . . . . . . . . . . . . 59

19 11.1 mm Shackle Test Data . . . . . . . . . . . . . . . . . . . . . . 59

6


1 Introduction

Indoor climbing is a popular sport in the UK and world wide. The majority of

indoor climbing routes are top rope climbs meaning that the rope is hung down

from above the climber and connected to the harness. The climber is then belayed

from the ground by their partner using a belay device. This can be clearly seen in

figure 1. The rope travels through the belay device up to an anchor point (upper

caribiner in the figure 1) then back down to the climber on the wall.

Figure 1: Diagram of a typical top rope setup. [Vogel(2002)]

Previous work on climbing ropes has focused on how knots affect the strength

of climbing ropes ([Brown(2008)]), how lowering cycles affect the number of falls

a rope can sustain ([Vogel(2002)]). Other research has investigated the strength

of caribiners under static and dynamic loads ([McGuinnity(2004)] [Garratt(2006)]

[Jackson(2008)]).

Although there has been research into the number of falls a rope can take in a

top rope situation there is no information available as to what effect anchor points

and different designs of belay device have on the overall strength of a dynamic

rope. Many people use caribiners or a length of rope as an anchor, some indoor

centres use pulleys but there is no general consensus on what is a suitable anchor.

As for belay devices, there are many available from a simple Italian hitch to the

“bug” design, to the expensive self locking devices such as the Petzl GriGri.

7


All belay devices work in the same way, by increasing the friction in the system

to allow the belayer to hold the climber if they should fall. In an Italian hitch this

friction is provided by rope to rope and rope to metal contact, in a “bug” the

friction is provided by rope to metal contact as well as introducing sharp bends

into the rope. In a GriGri the rope is placed in a cam device which moves with

the friction of the rope and locks it between the cam and the casing.

During this project the effect of different belay devices on the overall strength

of the rope was tested before focusing on one particular device, the Black Diamond

ATC and how use affected the device and it’s effect on the rope. After the rope

tests were carried out a new and used ATC were cut and mounted in resin to allow

the crystal structure to be viewed.

A cursory investigation into how the anchor point diameter affect the strength

of the rope was also carried.

8


2 Equipment

This section describes the equipment used in this investigation. In the pictures

of belay devices the top of the picture is the live end of the rope, that is the end

which goes to the climber, and the bottom of the picture is the dead end, the end

which the belayer holds on to.

2.1 DMM Aero HMS Carabiner/Belay Master

The DMM Aero HMS is described as the “classic HMS belay biner” which is why it

was chosen for this investigation. The HMS is a screw gate carabiner constructed

of hot forged aluminium. It has a rated strength on the long direction of 25 kN

and 10 kN when loaded across the gate as shown in figure 2.

The Belay Master is a variation of the Aero HMS with a plastic clip to prevent

cross loading. In this investigation it was used for the Italian hitch to prevent the

hitch from moving round the carabiner.

The carabiners are slightly oval on shape where the rope passes over it. They

have a diameter of 12.7 mm in the direction parallel to the incoming and out going

rope and 10.9 mm in the narrower direction. This implies a radius of curvature of

approximately 5.5 mm round the carabiner.

Figure 2: Picture of DMM Aero HMS Carabiner

2.2 Black Diamond ATC

The Black Diamond ATC is an entry level belay device which consists of single

piece of aluminium with a steel wire hoop. It is designed to be used with either

9


single or double ropes between 7.7 and 11 mm in diameter.

To use the ATC a loop is made in the rope and passed through the slot before

being secured with the wire loop into a locking carabiner as shown in figure 3.

The three worn ATC devices were obtained from the Fordell Firs National

Scout Activity Centre and have had approximately 11 months of hard use. Most

of that time they had been outside and used with dirty ropes.

Figure 3: Picture of Black Diamond ATC set up

2.3 Black Diamond ATC Sport

The Black Diamond ATC Sport is very similar design to the ATC except that it

is designed only for a single rope and has an added high friction mode. The high

friction mode is achieved though an extended piece of the device compared to the

ATC which has ridges on it to increase friction on the rope (shown in figure 4b).

The device is set up in exactly the same way as the ATC in either high friction

(shown in figure 4a) or normal friction modes.

10


Figure 4: (a)Picture of Black Diamond ATC Sport set up (b)Picture of high frictiongroves

2.4 Italian Hitch

The Italian hitch is the simplest method of belaying as it requires no device to be

used. It is suitable for any rope thickness as it is self adjusting and doesn’t rely

on any device. It is created by passing the rope through the carabiner, making a

loop in the tail of the rope and passing it onto the carabiner. The final result is

shown in figure 5. The Italian hitch is different from the other devices tested as it

is the only one which relies on rope to rope contact for increasing the friction. All

the other devices tested have relied on rope to metal contact.

Figure 5: Picture of Italian Hitch set up

11


2.5 DMM Figure of 8

A figure of 8 is primarily used for abseiling but can be used as a belay device.

It is suitable for any rope thickness and is rated to 24 kN. It is constructed from

aluminium which is 13 mm in diameter for the large loop and 10 mm in diameter

for the small loop.

The rope is fed through as shown in figure 6.

Figure 6: Picture of DMM Figure of 8 set up

2.6 Anchor Point

In top rope climbing many things are used as anchors, the most common setup is

a carabiner but it can easily be a pulley, a pipe or another piece of rope. Figure 7

shows the typical way in which an anchor point is set up.

In order to test how different diameters of anchor point affect the strength of

the climbing rope, shackles of 11.1 and 19.2 mm and a 56 mm eye splice insert

were used (8).

12


Figure 7: Picture of Anchor set up

Figure 8: Picture of Anchors used. a) 56 mm, b) 19.2 mm, c) 11.1 mm

2.7 Tinius Olsen Tensile Strength Testing Machine

The standard test for a climbing rope is UIAA drop test in which a mass of 80 kg

is dropped from a height of 5 m onto 2.8 m of rope to simulate a severe fall with

a fall factor of 1.77. As such a machine is unavailable the Tinius Olsen is used as

a replacement. This was considered to be a suitable replacement as the properties

13


of the rope determine the breaking load and not the method the force is applied

([Casavola and Zanatoni(2002)]).

The Tinius Olsen tensile testing machine (shown in figure 9) is a vertical pull

testing machine with a maximum force of 200,000 lbs (890,000 N). The origi-

nal analogue scale is complimented by a computer based recording system which

records the extension between the cross heads and the force exerted between them

at user defined time intervals. For this investigation it was set to a maximum force

of 10,000 lbs on the analogue scale in 10 lb increments.

Figure 9: Picture of Tinius Olsen Tensile Testing MachineShowing 1) Analogue Scale, 2) Tinius Olsen, 3) Computer Recorder.

2.7.1 Rope Clamps

In order to secure the rope to the crossheads of the tensile testing machine, drums

were constructed of parallel steel plates with a 100 mm diameter steel drum in the

centre. The rope was wrapped around the drums twice and secured with a clamp

and an overhand knot to stop it slipping. This can be seen in 10a.

14


Figure 10: Picture of a) Rope Attachment b) Anchor Attachment

2.7.2 Anchor Point

For the anchor point test the bottom rope clamp was replaced with a 1/2” shackle

to allow the attachment of the different sized shackles used for the test. This can

be seen in 10b.

2.8 DMM Statement Dynamic Climbing Rope

DMM Statement rope is an entry level dynamic climbing rope which is widely used

in both indoor and outdoor climbing. This rope is a 12 core synthetic rope with a

braided sheath.

The rope used in this investigation was obtained directly from DMM in a single

150 m length to ensure it came from a single batch and to get consistent properties

in every test.

15


Figure 11: Picture of DMM Statement Dynamic Rope Showing Sheath and Cores

Diameter 10 mmWeight 62 g/mFalls 6Impact Force 8.9 kN% Sheath 37

Table 1: Properties of DMM Statement Dynamic Climbing Rope

16


3 Method

Throughout the experiment each rope was given a unique ID beginning CM fol-

lowed by a number. All data files were named the to match the rope they related

to. A table of information on each rope is given in table 8 on page 55.

A minimum of 3 tests were performed for each device and a test was deemed to

be to be valid when the rope broke within the section of rope which was between

the drums. A test was deemed invalid if the rope broke at a place which had been

on the securing drums as this may have been damaged by contact with the surface

of the metal.

3.1 Straight Pull Test

For the straight line test the rope was cut into 2.85 m lengths using the gas hot

knife which also seals the ends to prevent slippage of the sheath. The ropes were

then labelled at each end with the sample ID and the clamp it was secured in

using masking tape. The centre was marked along with marks 100 mm either side

of the centre to make a known gauge length.

The rope was then wrapped round the rope drums twice before being secured

between clamps and an overhand knot tied to prevent it slipping. This was set

up so that the centre of the rope was centred between the clamps and the gauge

marks marked the point at which the rope left the drum.

The rope was then run up to 400lbs and relaxed back to zero to take slack out

of the system and tighten up the rope around the drums. The computer was then

set up to record the extension (in mm) and force (in lbs) every 2 seconds and the

test was set running with the crossheads moving at 3 mm/s.

At 1000 lbs the crossheads were stopped and the gauge length was measured

and recorded.

The experiment was then set running again and continued until the rope

snapped. The maximum breaking load was recorded off the analogue scale on

the Tinius Olsen machine and the computer data saved.

17


3.2 Belay Device Test

3.2.1 New Devices

For the belay tests 2.80 m of rope was cut using the hot knife cutter and again the

ends were taped and labelled and the centre of the rope marked.

The rope was then threaded through the belay device being tested and the

centre mark was lined up as described in table 2 before being taped in place with

masking tape. The rope ends were attached to the Tinus Olsen in the same way as

for the straight pull test and the tape removed. The carabiner holding the belay

device was tied to the upright on the Tinius Olsen with a piece of spare rope to

restrain it when the test rope snapped. Care was taken to have enough slack in

this rope so as not to influence the measurement of the force on the system.

The samples were then run up to 400 lbs to remove the slack from the system

before being returned to zero. The computer was then set up as for the straight

pull test and the test set running until the test rope snapped. The Tinius Olsen

was then stopped and the computer data saved and maximum force recorded from

the analogue gauge.

Test Rope Centre PositionATC on carabiner

ATC Sport on carabinerFigure of 8 centred on the body between the two “loops”

Italian Hitch centre on the dead end ofthe rope as it crosses the live end

Table 2: Table Describing the Positioning of the Centre point on the rope in eachBelay Device.

3.2.2 Worn Black Diamond ATC

For the worn ATC tests the most worn side of the device was chosen and marked.

The most worn edge was chosen to be the bottom as this is consistent with what

would be expected under normal use. The remainder of the test was carried

out in as described for the new device tests above except that the carabiner was

18


fixed in the diagonal position across the back of the device with masking tape.

This decision was made after analysis of the initial results from the new devices.

Masking tape was used as it breaks at a low load and will not influence the results

of the test.

3.2.3 Microscopic Analysis

Once all the rope strength tests were carried out the new ATC and one of the worn

ATC’s were cut along the long axis of the slot and mounted in resin before being

polished and etched using Kellers Etch. These samples were then viewed under a

microscope to see any changes in the microscopic structure between new and used.

3.3 Anchor Test

For the anchor point tests 2.8 m of rope was cut using the hot knife and the ends

sealed. The ropes were marked and recorded with their individual ID as before.

For the anchor point tests the bottom rope clamp was replaced with a 1/2”

shackle and various shackles were attached to it. The rope was threaded through

the test shackle and both ends were secured to the top rope clamp as for the

straight rope and belay device tests. The point at which the rope met the shackle

was marked so there was an accurate reference position and marks were also made

on both strands of the rope approximately 20 mm from the shackle.

The tinius olsen was then run up to 400lbs then returned to zero to remove the

slack form the system. The computer was then set recording and the machine set

running until the rope snapped. The computer data was saved and the maximum

load was recorded from the analogue scale.

19


4 Results and Analysis

Once the data was recorded it was imported into Microsoft Excel and the force

converted from lbs to Newtons by multiplying the conversion factor 4.448. This

data was then imported into Easyplot and the force was plotted as a function of

the extension.

The mean value of the maximum force was calculated using equation 1 and the

standard deviation estimated using equation 2.

x̄ =Σxin

(1)

σ =

√∑ni=1 (xi − x̄)2

(n− 1)(2)

For the belay device tests in order to provide a meaningful comparison between

each device an efficiency was defined as in equation 3.

η =average max load with device

average max straight line load(3)

For the anchor point tests a similar efficiency was defined as in equation 4

η =average max load at given diameter

average max load for 56 mm eyelet insert(4)

4.1 Straight Pull Test

The initial two test on the straight pull, CM1 and CM2, were discounted because

they broke in a portion of the rope which started off on the securing drum. After

looking at the set up, the clamp position was changed so that it could not come

into contact with the rope as this was the suspected cause of the breaks in these

first two tests. The initial and final positions are shown in figure 12 on page 21. In

these initial tests the clamps were positioned between the rope drums, by moving

them to the back side of the drums the problem was solved and the next three

tests broke in the gauge length which had started out in the free space between

the drums. The breaking of the rope is almost instantaneous, the core and sheath

20


Figure 12: Picture showing a) initial clamp position, b) revised clamp position toremove the possibility of the clamp coming into contact with the rope.

both break at the same time with very little warning.

The average maximum force in the straight line pull tests was 20,090 N with a

standard deviation of 1.47% (296 N).

This result gives a good baseline load to compare how the rope strength varies

with the use of different belay devices. With such a low standard deviation these

result can be taken as typical for this rope. The individual results for each test

are shown in table 9 on page 56.

The plot in figure 13 (page 22) shows how the load on the rope varies as the

extension of it is increased. As can be seen in the figure the force increases quite

smoothly until about 900 mm of extension then becomes quite jagged. This is

because the friction between the rope and the securing drums is not enough to

stop the rope slipping under the tension so what is seen here is the rope being

pulled off the drums. Since rope is being pulled off the drums this is increasing the

length of rope between cross heads at a rate greater than they are moving apart

so we see a reduction in the load on the system.

The plot also shows broadly similar loading curves for all three samples tested

so the results are believed to be reliable.

21


Figure 13: Plot of Load as a function of Extension for a straight rope with nobelay devices to provide a baseline for all future tests.Average load of 20,090 Nwith a standard deviation of 1.47%

22


4.2 New Belay Devices

4.2.1 Black Diamond ATC

For the Black Diamond ATC belay device 4 initial tests were run giving an average

breaking load of 7,361 N with a standard deviation of 5.35% (394 N). After the

graphs for the initial test were analysed 6 more test were carried out and the

average breaking load was then 7,348 N with a standard deviation of 3.74% (275

N). Using equation 3 an efficiency of 36.6% of the strength of the straight rope

was calculated. The individual results for each test are shown in table 10 on page

56.

When the rope was in the ATC it went through two 90o bends at the live end

entrance and the dead end exit as well as turning through 180o round the securing

carabiner. From looking at the test ropes the ropes consistently break at either

the entrance or exit but didn’t show a preference in the four initial tests with two

breaking at the live end and two breaking at the dead end. It is believed this

is because of the tight radius of curvature the rope is forced to follow acts like a

blade cutting through the rope under increased loads.

The setup used in this test is at the extreme end of the angles possible when

belaying in an actual climbing situation, more commonly the live end of the rope

will come in at a shallower angle and the dead end will exit at close to 90o .

Interestingly in figure 14 (page 25), showing the initial 4 results, there appear

to be two distinct load curves. Ropes CM6 and CM7 seem to follow a faster initial

loading up to an extension of 125 mm compared to ropes CM8 and CM9 before

following a more parallel track until the maximum load is reached. This could be

because although the ATC looks symmetrical there may be differences in finish of

the metal allowing it to slip easier in one side than the other though this is unlikely

to make such a large difference.

Alternatively the carabiner may have been settling in a different orientation on

the back of the device under tension which may have affected the way in which

the load is increased. This was backed up by the marks left by the carabiner on

the back of the device. There are two obviously different sets of marks. The first

set is approximately half way down the sides of the device where we would expect

the carabiner to sit under normal circumstances. The second set of marks are in

23


diagonally opposite corners implying that the carabiner had twisted under loading.

Taking more measurements fixing the orientation of carabiner on the back of

the device to test this hypothesis has done little to clear things up. Figure 15

(page 26) shows the load curves for all the tests on the ATC. The tests where

the orientation of the carabiner on the back of the deviceis known is noted in the

legend. As can be seen test CM33 came in with a load curve lower than any other

results. Tests CM37 and CM44 to CM47 all follow a broadly similar curve to the

original curves of CM8 and CM9. None of the extra tests were comparable to CM6

and CM7.

Taking all the results into account a new theory was thought up. From figure

15 (page 26) it appears that the higher the initial gradient of the load curve the

shorter the final extension of the rope. This was backed up by the fact that

ropes CM6 and CM7 showed the fastest increase in load and broke at the lowest

extensions whereas rope CM33 had the slowest increase in load and the longest

final extension. The shorter final extension implies that the initial length of rope

between the clamps was shorter. As the initial distance between the clamps was

not recorded during testing more work will be required to confirm this.

The load curves do not appear to have an effect on the final breaking load of

the rope in the test so the results were considered to be valid.

24


Figure 14: Plot of Load as a function of Extension for the Black Diamond ATCbelay device initial tests showing tests CM6 to CM9 showing the two different loadcurves. Average load of 7,361 N with a standard deviation of 5.35%

25


Figure 15: Plot of Load as a function of Extension for Black Diamond ATC belaydevice tests showing all tests. It shows that the orientation of the carabiner doesnot affect the load curve it is more likely to be the initial length of rope betweenthe crossheads.Average load of 7,348 N with a standard deviation of 3.74%

26


4.2.2 Black Diamond ATC Sport

For the Black Diamond ATC Sport belay device 3 tests were run giving an average

breaking load of 12,380 N and a standard deviation of 3.45% (427 N). Using

equation 3 an efficiency of 61.6% of the strength of the straight rope was calculated.

The individual results for each test are shown in table 11 on page 57

In this test the rope consistently broke on the live end at the top edge of the

device. Although the top edge of the device looks very similar to that of the ATC,

on closer inspection it has a much larger radius of curvature of approximately 2

mm and it is believed this is the main cause for the reduced loss of strength.

From this test all that can be said about the high friction part of the device is

that it does not reduce the strength of the rope more than the top edge.

Figure 16 (page 28) shows that the load curves all follow the same broad

pattern. The damage on the back of the device in this case showed that the

carabiner was consistently in the same place approximately half way down the

device as would be expected under normal use. Due to the design of the device

there is no way for the carabiner to twist under load in this case.

27


Figure 16: Plot of Load as a function of Extension for Black Diamond ATC Sportbelay device tests.Average load of 12,380 N with a standard deviation of 3.45%

28


4.2.3 Figure of 8

For the DMM Wales Figure of 8 (FO8), 3 tests were run giving an average breaking

load of 17,080 N with a standard deviation of 6.31% (1080 N). Using equation 3

an efficiency of 85.0% of the strength of the straight rope was calculated. The

individual results for each test are shown in table 12 on page 57.

After the initial test it was noticed that the FO8 had been bent by 12o . This

does not affect the overall shape in the area of the device through which the rope

passes so it was decided to continue with the remaining tests.

The highest breaking load was the first test (CM13) before the FO8 was bent,

the lowest was the 2nd test (CM14) and the final test was almost exactly on the

average. This may imply that after the initial test the effect on the rope strength

changed due to the bending of the FO8 but more data would be needed to confirm

this.

Figure 17 (page 30) shows the slight variations in the load curves between the

three tests. It seems that when the load increases faster we get a lower maximum

load.

29


Figure 17: Plot of Load as a function of Extension for Figure of 8 device test.Average load of 17,080 N with a standard deviation of 6.31%

30


4.2.4 Italian Hitch

For the Italian Hitch, 3 tests were run giving an average breaking load of 12,340

N with a standard deviation of 2.32% (286 N). Using equation 3 an efficiency of

61.4% of the strength of the straight rope was calculated. The individual results

for each test are shown in table 13 on page 57.

When the Italian hitch is loaded the live end of the rope is straight between

the carabiner and the top cross head. The dead end of the rope loops round the

live end and through the carabiner and is then attached to the bottom crosshead.

As the load is increased most of the movement is in the dead end as the loop is

tightened around the live end. It appears from looking at the rope samples that

the dead end of the rope acts as an edge and puts pressure on the live end of the

rope as in the tests the rope consistently broke at this point.

Figure 18 (page 32) shows that the load curves for the Italian hitch are almost

identical with each other.

31


Figure 18: Plot of Load as a function of Extension for Italian Hitch tests.Averageload of 12,340 N with a standard deviation of 2.32%

32


4.3 Worn ATC Device

4.3.1 Rope Tests

For the tests on the worn Black Diamond ATC devices 3 tests were carried out on

each of the 3 devices. The average results for each device and overall average are

shown in table 3. From general observations, device 1 was the most visually worn

of the 3 tested and device 3 was the least worn. Taking that into account it can

be seen that the more worn a device is the lower the breaking load of the rope.

The average maximum load over all 3 worn devices is 5,767 N with a standard

deviation of 6.95 % (401 N) this is a 21.7% reduction in the strength compared

to a new device of the same design and a 71.3% reduction over the straight rope

tests. Table of all test results for the 3 worn devices can be found in tables 14 15

and 16 on 58.

This reduction occurs because the used devices have worn edges where the rope

runs over them in use. These worn edges have smaller radii of curvature than the

new device and thus act as a sharper edge cutting into the rope.

The load curves for the 3 devices are shown in figure 19 (page34). It can be

seen that all 3 tests on all 3 devices follow the same general shape except CM34

which is slightly lower than the other tests. The slight bump in test CM42 between

150 and 200 mm was when the safety rope became tangled and was released.

Device Average Breaking Standard Strength Lost Compared

ID Load (N) Deviation (%) To New Device (%)

1 5352 6.97 27.3

2 5797 3.10 21.2

3 6153 3.57 16.4

Average 5767 6.96 21.7

Table 3: Worn Black Diamond ATC Belay Device Average Test Data

33


Figure 19: Plot of Load as a function of Extension for Worn Black Diamond ATCbelay devices. Average load of 5,767 N with a standard deviation of 6.95%

34


4.3.2 Microscopic Analysis

After the ATC devices were cut and polished they were photographed in a macro

scale. Figure 20 (page 36) shows the cross section of the device from front to back

through the slot in the device. Figure 20a is the new device and figure 20b is the

worn device. The top of the picture is the back of the device and the scale visible

is in mm. The images do not show exactly the same cross section, image (a) is

from almost the centre of the slot and image (b) is offset to the outside edge.

Looking at both samples together the wear on the working edge can clearly be

seen. In figure 20b the bottom of left hand cross-section is the most worn edge,

it can be seen that the wear is significant and the metal has been worn to a far

smaller radius of curvature than on the new device. The metal in this area has

been removed cleanly by abrasion rather than deformation. This is backed up by

figure 21 (page 36) which shows the termination of the grain boundaries at the

edge of the device to be clean and without deformation.

The second feature to notice in these images is the fibre structure in the cen-

tre of the material, these can be seen more clearly in figure 22 (page 37). This

implies that the metal was initially extruded and the grains of aluminium have

been stretched and elongated so much that they now resemble fibres. At the edges

of the device these fibres are deformed which implies that the material has been

reheated and forged into its final shape. This deformation can be clearly seen in

figures 23 (page 37) and 24 (page 38). At the large radius end (i.e. the back of

the device) as shown in 23 (page 37) the metal has been forced together to form a

single piece of metal. At the small radius end (i.e. the front of the device) shown

in figure 24 this can be seen more clearly. At this end the material has not fused

correctly into a single piece and has left a formation defect. In 24a and c there is

a clear discontinuity where the metal has been forced together. The same can be

seen in 24b and d. These cracks are deformation cracks, this is known since the

grain structure on either side of the crack is different. If these cracks had formed

during use the grain boundaries would match on either side of it. The cracks are

large enough to be seen with the naked eye and have been photographed and are

shown in figure 25 (page 39).

35


Figure 20: Macro photo of a) New ATC and b) Worn ATC showing approximatepositions of micro images. 1. large radius 23, 2. mid section 22, 3. inside edge 21and 4. small radius 24.

Figure 21: Micro photos of the inside edge of a) New ATC and b) Worn ATC at200x magnification show that there is no change in crystal structure due to wearon the working edge.

36


Figure 22: Micro photos of the mid section of a) New ATC and b) Worn ATC at50x magnification showing the fibre structure of the aluminium.

Figure 23: Micro photos of the large radius of a) New ATC and b) Worn ATC at50x magnification showing how the aluminium is forced together when forged intoits final shape.

37


Figure 24: Micro photos of the small radius of a) New ATC and b) Worn ATCat 50x magnification and c) New ATC and d) Worn ATC at 200x magnification.Approximate positions of c) and d) are marked by the white boxes in a) and b).These pictures show formation cracks in both the new and old device, if they werecracks due to use the grain boundaries would match across the crack.

38


Figure 25: Macro photos of the small radius of a) New ATC and b) Worn ATCshowing formation cracks as visible in the micro photos.

4.4 Anchor Point

For the Anchor Point tests the 56.6 mm Eyelet was taken as the baseline strength

because it does not appear to affect the strength of the rope overall. During the

tests of the eyelet the rope broke in a section of the rope which was on the drum in

all 3 cases. The average maximum load for the eyelet was 39172 N with a standard

deviation of 1.25% (490). As we have doubled up the rope strands between the

cross heads of the Tinius Olsen it was expected that the load which is produced

would double. The maximum average load for a single strand of rope was 20,090

N so double this would be 40,180 N. Taking into account the standard deviations

(SD) in the readings these values agree to within error. As shown in table 4 (page

39)the upper limit of the double strand overlaps with the lower limit of the single

strand ×2. By taking this into account it is believed that these results are valid

even though the ropes broke on the drum.

Strand Average minus SD Average Average plus SDSingle 19794 20090 20386

Single ×2 39588 40180 40772Double 38682 39172 39662

Table 4: Single/Double Strand Comparison table showing how the results for asingle strand compare to the results of 56.6 mm diameter anchor point.

39


In table 5 the average results for the 3 different diameters are shown. As

expected the average maximum load the rope can hold decreases as the diameter

decreases. This is believed to be because the radius of curvature of the rope is

decreased in the same way as for the different belay devices above.

The original plan was for tests to be carried out down to 4 mm but the shackles

below 10 mm broke well below the rope breaking load so no data could be obtained.

Test Average Max Load (N) Std Dev (%) Strength Lost (%)56.6 mm 39172 1.25 Reference Load19.2 mm 36726 2.73 6.211.1 mm 31596 4.47 19.3

Table 5: Average Rope Strength for Varying Diameters of Anchor Point and thestrength lost over the reference load.

Figures 26 (page 41), 27 (page 42) and 28 (page 43) show the load curves for

the different diameters used in decreasing order.

40


Figure 26: Plot of Load as a function of Extension for a 56.6 mm Eyelet.Averageload of 39,172 N with a standard deviation of 1.25%

41


Figure 27: Plot of Load as a function of Extension for a 19.2 mm Shackle.Averageload of 36,726 N with a standard deviation of 2.73%

42


Figure 28: Plot of Load as a function of Extension for an 11.1 mm Shackle. Averageload of 31,596 N with a standard deviation of 4.47%

43


4.5 General Observations

One feature which stood out in all the graphs which were plotted was the gradient

change in the load curve. When all the data was looked at there was a consistent

change from a steep gradient to a shallower one. Taking one load curve from each

set of tests (shown in table 6 on page 45) and recording the extension and load

where the change occurred it can be seen that it occurs at a specific load of 1918

N with a standard deviation of 7.7%.

Without the anchor point tests it initially appeared that it could have either

a specific extension or load but with the inclusion of the anchor point tests it is

more probable it is an specific load. The extension of the rope in the anchor tests

is twice the recorded extension because of the double length of rope. Taking this

into account the average extension is 134 mm and the standard deviation is 22.8%.

A standard deviation this large implies that there is little confidence in the results

being of any significance.

The reason behind this change is unknown. Working theories are it is a property

of the core or sheath of the rope where the stiffness of the rope decreases after a

certain load is applied. An alternative theory is that there was an issue with

the Tinius Olsen’s computer recorder but this is unlikely as it was calibrated and

certified during testing.

44


Position of Change in GradientTest Rope Extension (mm) Load (N)

Straight Pull 100 1850BD ATC (Top Curve) 105 1740

BD ATC (Bottom Curve) 140 1740BD ATC Sport 183 2075

FO8 155 1916Italian Hitch 124 1826Worn ATC1 172 1933Worn ATC2 161 1907Worn ATC3 150 1868

11.1 mm Shackle 92 (46 measured) 209519.2 mm Shackle 118 (59 measured) 223556.6 mm Eyelet 106 (53 measured) 1836

Average 134 1918Std Dev 30.5 148.5

Std Dev (%) 22.8 7.7

Table 6: Table showing the Position of Change in Gradient in on test for eachdevice and the average values.

5 Conclusions

5.1 Belay Devices

Figure 29 (page 47) and Table 7 (page 46) show a summary of the maximum load

achieved by each belay device and the standard deviation in the measurements.

As can be seen from the results the DMM figure of 8 keeps the most strength in

the rope and the Black Diamond ATC keep the least. The ATC Sport and the

Italian Hitch have almost identical strength losses.

From looking at the various designs of belay methods the conclusion was that

the reduction in the strength of rope is determined by the radius of curvature

of the edge the rope was run over. This was supported by the fact that the

Black Diamond ATC has the lowest average breaking load and smallest radius

of curvature of all the devices tested. Conversely the DMM Figure of 8 has the

highest average breaking load and also has the largest radius of curvature. This

45


Device Average Breaking Standard Strength Lost ComparedLoad (N) Deviation (%) to Straight Rope (%)

Straight Rope 20090 1.47 Reference LoadATC 7348 3.74 63.4

ATC Sport 12380 3.45 38.4Italian Hitch 12336 2.32 38.6Figure of 8 17080 6.31 15.0

Table 7: Summary Table showing the breaking load, standard deviation and %strength lost of belay devices tested.

was also backed up by the worn ATC tests which had lower breaking loads than

the new ATC and also a smaller radius due to wear.

From the microscopic analysis there is no difference between the new and used

Black Diamond ATC structure. The wear on the metal is by abrasion and no

deformation is present. It also shows that the device is probably constructed of

extruded aluminium which is then reheated and forged into its final shape.

The testing shows that belay devices have a marked effect on the strength of

climbing rope with a loss of between 15% and 65% depending on the device. Even

with the largest reduction in strength from the Black Diamond ATC the rope still

held over 7300 N. In a top rope setup the main load on the rope is the climber and

falls will be over short distances compared to the length of the rope so the forces

applied will be far lower than the breaking strength of the rope. [Vogel(2002)]

shows that the maximum force on rope in a typical top rope setup with an 80kg

climber is 785 N so that is a factor of 9.2 safety margin over the lowest load

achieved in testing for new devices and a factor of 6.8 over the lowest load achieve

in the used devices. [Vogel(2002)] also shows that the load at the belay device is

significantly less than the weight of the climber at 440 N therefore providing an

even larger safety margin of 16.7 in the the new device and 12.1 in the used device.

For the other devices the safety margins were even higher. The reduced load at

the belay device is due to the friction between the rope and the anchor used.

46


0

50

00

10

00

0

15

00

0

20

00

0

25

00

0

01

23

45

67

Average Max Load

Test

ID

Stra

igh

t

ATC

ATC

Sp

ort

Gri

Gri

Ital

ian

Hit

ch

FO8

Figure 29: Graph of comparison of Belay Devices with Standard Deviation

47


5.2 Anchor Point

Although minimal testing was successful in this area it can be seen that a reduction

in the diameter of the anchor point leads to a reduction in the overall strength of

the rope. How the diameter affects the rope strength is shown in figure 30 with

the limited data obtained. More work is required to find method of testing smaller

diameter anchors to give a better picture of the how the strength varies.

In climbing the most common anchor point is a carabiner which is usually

around 10 mm in diameter. From the testing completed the use of a carabiner

will result in about a 20% loss in rope strength. While this is a significant loss

the rope strength is still far higher than required under usual circumstances and

in most cases outweighed by the strength lost in the belay device.

48


0

5000

10000

15000

20000

25000

30000

35000

40000

45000

010

20

30

40

50

60

Average Maximum Load

Dia

me

ter

(mm

)

An

cho

r P

oin

t D

iam

ete

r

Figure 30: Comparison of Braking Strength Against Anchor Point Diameter

49


6 Further Work

Future work building on this project should include further analysis of anchor point

diameters and include the design of a suitable test rig to work with diameters less

than 10 mm. This will lead to a better understanding of how the radius of curvature

affects the breaking strength of a rope.

Also further investigation into the properties of the rope and the unusual change

of stiffness under load should also be considered.

This project focused on what was essentially a static load being applied to the

rope as this is analogous to the top rope climbing case. In lead climbing the rope

is under a more dynamic load and this would also warrant investigation to see how

a significant fall onto a rope in a belay device affects it’s overall strength.

50


7 Acknowledgements

Firstly I would like to thank Dr Andrew McLaren for allowing me to do this project

and providing guidance on where to go. My thanks must also go to Mr Andrew

Crockett for his assistance in the lab and his wealth of experience in running the

machines and knowledge of previous work.

I would also like to thank Mr James Kelly for preparing the metal samples and

his assistance in deciphering what they were telling me.

I also wish to thank the staff of Cotswold Silverburn and the Glasgow Climb-

ing Centre for allowing me to sketch and photograph various pieces of climbing

equipment without actually buying anything and also providing me with some

background knowledge of general climbing setups.

DMM Wales have also been very helpful with supplying of the rope and tech-

nical details at a reduced cost.

Fordell Firs have been generous in donating the used Black Diamond ATC

belay devices.

Finally I wish to than family and friends for putting up with having to listen

me talk about rope and belay devices for the last few months.

51


References

[Brown(2008)] Alasdair Brown. The strength of knots in dynamic climbing rope.

Master’s thesis, University of Strathclyde, 2008.

[Casavola and Zanatoni(2002)] P. Casavola and C. Zanatoni. Rope testing and

Wear: Equimpment of the CMT. In Nylon and Ropes for Mountaineering and

Caving. Club Alpino Italiano, Commissione Materiali e Tecniche, March 2002.

[Garratt(2006)] Nathan R. Garratt. The affects of use on the strength of climbing

karabiners. Master’s thesis, University of Strathclyde, 2006.

[Jackson(2008)] Natalie Jackson. Dynamic testing of karabiners. Master’s thesis,

University of Strathclyde, 2008.

[McGuinnity(2004)] Steven McGuinnity. What determines the strength of climb-

ing karibiners. Master’s thesis, University of Strathclyde, 2004.

[Vogel(2002)] Dr Ing Wolfram Vogel. Safety loss of mountaineering ropes by low-

ering cycles in toprope climbing. In Nylon and Ropes for Mountaineering and

Caving. Club Alpino Italiano, Commissione Materiali e Tecniche, March 2002.

52


A Table of Rope Info

Rope ID Test Info Comments

CM1 Straight Pull Broke on drum

CM2 Straight Pull Broke on drum

CM3 Straight Pull Broke in Gauge length



CM6 Black Diamond ATC Broke top edge

CM7 Black Diamond ATC Broke bottom edge

CM8 Black Diamond ATC Broke top edge

CM9 Black Diamond ATC Broke bottom edge

CM10 Black Diamond ATC Sport Broke top edge



CM13 Figure of 8 Broke on top of loop



CM16 Italian Hitch Broke live end at

rope to rope contact





CM19 GriGri Poor test design severely

damaged GriGri

CM20 4 mm shackle Shackle broke at 2210 lbs

CM21 5.5 mm shackle Shackle broke at 2700 lbs

CM22 10 mm shackle Same rope as CM21

different file name

Rope broke at 5060 lbs

Continued on next page

53


Table 8 – Continued from previous page


CM23 56.6 mm Eyelet Broke on drum



CM26 19.2 mm Shackle Broke at centre

of loop


of loop


of loop

CM29 5 mm rated Shackle Broke shackle at 1056 lbs

CM30 11.1 mm shackle Broke at centre

of loop


of loop


of loop

CM33 ATC, Carabiner Horizontal Broke bottom edge

CM34 Worn ATC1 Broke bottom edge



CM37 ATC, Carabiner Diagonal Broke bottom edge







CM44 ATC, Carabiner Horizontal Broke top edge

CM45 ATC, Carabiner Horizontal Broke top edge

Continued on next page

54


Table 8 – Continued from previous page


CM46 ATC, Carabiner Diagonall Broke top edge

CM47 ATC, Carabiner Diagonal Broke top edge

Table 8: Rope Description and Comments

55


B Tables of Test Data

B.1 Staight Pull

Rope Overall Gauge Length Gauge Length Max Breaking Max Breaking

ID Length unloaded 1000lbs Load Load

(m) (mm) (mm) (lbs) (N)

CM1 2.85 200 268 4330 19260

CM2 2.85 200 270 4380 19482

CM3 2.85 200 270 4460 19838

CM4 2.85 200 260 4590 20416

CM5 2.85 200 274 4500 20016

Table 9: Straight Pull Test Data

B.2 Belay Devices

Rope Overall Max Breaking Max Breaking

ID Length (m) Load (lbs) Load (N)

CM6 2.85 1750 7784

CM7 2.85 1570 6983

CM8 2.85 1590 7072

CM9 2.80 1710 7606

CM33 2.80 1640 7295

CM37 2.80 1660 7384

CM44 2.80 1640 7295

CM45 2.80 1570 6983

CM46 2.80 1690 7517

CM47 2.80 1700 7562

Table 10: Black Diamond ATC Test Data

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CM10 2.80 2680 11921

CM11 2.80 2800 12454

CM12 2.80 2870 12766

Table 11: Black Diamond ATC Sport Test Data



CM13 2.80 4100 18237

CM14 2.80 3620 16102

CM15 2.80 3800 16902

Table 12: DMM Figure of 8 Test Data



CM16 2.80 2820 12543

CM17 2.80 2800 12454

CM18 2.80 2700 12010

Table 13: Italian Hitch Test Data

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B.3 Worn ATC Device



CM34 2.80 1150 5115

CM35 2.80 1300 5782

CM36 2.80 1160 5160

Table 14: Worn Black Diamond ATC 1 Test Data



CM38 2.80 1260 5604

CM39 2.80 1310 5827

CM40 2.80 1340 5960




CM41 2.80 1440 6405

CM42 2.80 1360 6049

CM43 2.80 1350 6005


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B.4 Anchor Points



CM23 2.80 8920 39676

CM24 2.80 8800 39142

CM25 2.80 8700 38698

Table 17: 56.6 mm Eyelet Test Data



CM26 2.80 8420 37452

CM27 2.80 8350 37141

CM28 2.80 8000 35584

Table 18: 19.2 mm Shackle Test Data



CM30 2.80 6920 30780

CM31 2.80 7470 33227

CM32 2.80 6920 30780

Table 19: 11.1 mm Shackle Test Data

59

Effect of Belay Devices and Anchor Points on Dynamic Climbing Rope Strength

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