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The ELET, manifest various ways, awaiting testing
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knudenoggin


Feb 21, 2009, 11:46 PM
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The ELET, manifest various ways, awaiting testing
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ELET ::= Extension-Limiting Equalization Triangle

The ELET is a general schema. Its essence is the containment
of the powerponit connector, and the limited extension if one side
fails. How it gets implemented will vary on circumstances per user.
One could use two skinny HMPE slings vs. one, with each running the
perimeter of the triangle section (and tied to at anchor corners by
runners; or knotted into 'biners); or one could be Cloved into biners,
the other left unknotted, purely qua redundant item--untensioned
unless the other fails. There are also clever ways (maybe too
clever by half) of implementing the entire thing in cord; but this
is rather tricky and loses the low-friction aspect of the HMPE slings.

Courtesy of a local REI, here are some (URLinks to) photos of the
two ELETs: the first has Overhand eyeknots for connecting to, in
one sling; another sling is to be run through the connection purely
qua back-up structure, with a knot in it just to make it closer to
the working sling's encompassing size--but note the difference in
size on simulated 1-anchor failure.

In the 2nd set of pics, one sling forms the slide sides,
and it's bight-ends are tied to by the 2nd (60cm) sling,
which provided connector eyes to be clipped in or tied to.
I show a close-up of the knot in its three possible states:
as an eye-hitch like a sheet bend; as a sort of 2/3 of an
eye/loop knot (well, the other sling's part of that eye)
for the knot of the 1 holding anchor on failure;
and as an eye-hitch like a reverse sheet bend for
the failed-anchor-side knot. The connecting sling
could be replaced with one cordelette cord, twin
strands or parts of retired dynamic rope, single strand.

The knot makes use of the closed sling's "end", which
is a bight, for what I think will be better security (than
simply tying the sheet bend through the bight end vs.
the folded bight end (doubled parts, thus).

ELET + back-up: separate 60cm HMPE slings
(1st is start; 2nd is 1-anchor failed)
http://www.postimage.org/image.php?v=aV2x1eyr
http://www.postimage.org/image.php?v=Pq2M7Y4S

ELET in Two 60cm HMPE Slings
[ELET in 2 slings at start]
http://www.postimage.org/image.php?v=gx1h5zn9

[ELET in Two Slings knot close-up]
http://www.postimage.org/image.php?v=aV2x2ZiJ

[ELET in 2 slings w/anchor failure]
http://www.postimage.org/image.php?v=aV2x2FlA

[failed ELET in Two Slings holding-knot close-up]
http://www.postimage.org/image.php?v=Pq2M9xRA

[failed ELET in Two Slings failed-knot close-up]
http://www.postimage.org/image.php?v=gx1h69Ni


*knudeNoggin*

ps: Note the safety aspect of leaving the sales tags on the
gear, in case it fails, and your estate needs to get your money
back.

pps: Aric, I've been pinging you, but ... Sounds of Silence ?


(This post was edited by knudenoggin on Feb 22, 2009, 7:36 AM)


jeepnphreak


Feb 23, 2009, 9:08 AM
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knudenoggin wrote:


OK so Iam I seeing that right, It looks more like an american death triangle.


acorneau


Feb 23, 2009, 9:21 AM
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jeepnphreak wrote:
OK so Iam I seeing that right, It looks more like an american death triangle.

The white/grey sling is configured for an ADT, however the white/gold sling (if tied with enough slack in the upper strand) is not.

Why not just tie two limiter knots on a single sling (a la equalette) instead of three knots in two separate slings?


knudenoggin


Feb 23, 2009, 9:40 AM
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jeepnphreak wrote:
OK so Iam I seeing that right, It looks more like an american death triangle.
In being triangular, yes; in loading profile, no.
In the structure you highlighted, the looser, back-up sling
--in white & grey, w/Fig.8 knot in the center--,
would have the ADT effect, were it taking load ;
but this sling is purely back-up, and is loaded only if the
other sling fails. Put another way, the orange-tinged
sling, which bears the load, will have no (or little, if ...)
tension on the connecting span between anchor legs
(with the webbing stitching, here); you do not have
ADT force amplification on the anchors. (Btw, has
this force ever been actually tested ?? --I'm
thinking that the bark of its danger is worse than it's
bight, given friction.)

Moreover, note that it should generally be the case that this
ELET is connected to other cordage that attaches to anchor
points--this is just the powerpoint end, providing low friction
for equalization, and the closed circuit for limiting extension.

In the other ELET that I presented (slings tied together)
--voici:


cordelette cord could take the place of the upper sling, if one
wasn't using separate bits of cordage to tie into the anchors.

*kN*


shockabuku


Feb 23, 2009, 9:53 AM
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They all remind me of something to do with female anatomy and birth control.


hafilax


Feb 23, 2009, 12:21 PM
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That looks really dangerous with spectra slings. Tied spectra slings tend to slice through at low forces especially if the knots can slide and cinch adding heat to the equation. This has been shown repeatedly in girth hitched slings.

To be honest I don't like any of those configurations I would/will never use any of them for anchoring.


Partner j_ung


Feb 23, 2009, 12:56 PM
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knudenoggin wrote:
pps: Aric, I've been pinging you, but ... Sounds of Silence ?

I think he's traveling with his family. It's possible his wife hid his computer. Laugh


coolcat83


Feb 23, 2009, 1:07 PM
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shockabuku wrote:
They all remind me of something to do with female anatomy and birth control.

i saw the same thing...i gotta get my head out of my med books and back onto the rockCrazy


knudenoggin


Feb 23, 2009, 2:33 PM
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In reply to:
That looks really dangerous with spectra slings. Tied spectra slings tend to slice through at low forces especially if the knots can slide and cinch adding heat to the equation. This has been shown repeatedly in girth hitched slings.
To be honest ...

You'd cite a single case of this mythical "slice through" behavior,
which has come up repeatedly on this forum and repeatedly been
refuted. Your turn, now, I guess. Frown

But I figure that in most cases, as indicated above, that connecting
sling would be instead 7mm cord.

And, as noted, the ELET is a general structure, to be implemented
as one sees fit. The HMPE sling in the sliding span was suggested
for maximum equalization efficiency.

*kN*


hafilax


Feb 23, 2009, 3:12 PM
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http://www.alpinist.com/...-broken-sling-report
My quick search turned up the Mammut study cited in the article above. I admit that it's not as bad as I originally thought but they still caution against tying knots in dyneema slings. Note that loose knots that can cinch tend to break at lower forces due to the melting of the fibres as the strands slide in tightening.

Low stretch materials and tight bends just don't go well together. In tight bends the strands have different path lengths and the longest paths bear most of the load. That coupled with melting effects leads me to avoid tying dyneema slings together.

I take back my statement that they look dangerous but I still don't see any real advantage over existing systems. I think that for most cases the redundancy is overkill. Maybe if you're in serious rockfall terrain.

In the first system, why not just use the setup of the orange and white sling twice instead of adding the American triangle. If you want redundancy for that sling breaking why back it up with an inferior system?


The second system I still don't like because of my aversion to tying slings together but YMMV. If equalization with limited extension is a high priority I prefer something like this

or this


Truth be told I'm often content with a single sliding-X so who am I to talk. Pirate


adatesman


Feb 23, 2009, 5:06 PM
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knudenoggin


Feb 23, 2009, 5:43 PM
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hafilax wrote:
http://www.alpinist.com/...-broken-sling-report
My quick search turned up the Mammut study cited in the article above. I admit that it's not as bad as I originally thought but they still caution against tying knots in dyneema slings. ...
Low stretch materials and tight bends just don't go well together. In tight bends the strands have different path lengths and the longest paths bear most of the load. ...

You can find tests of the "Girth hitch" (sling-2-sling joint),
of some forms, at Kolin Powick's Black Diamond site;
they survived severe drops. You can find here some evidence
FOR melting, and evidence AGAINST cutting, as the HMPE slings
survived over nylon in slow-pull, but sometimes were what
broke in drop tests. But these are at SERIOUS big forces,
and after holding some fall(s). --a FAR cry from the undead
rumor of sling-cutting.
(I recall trying to get the Alpinist site to can that rubbish;
at least a 2nd (educated, this time) opinion is given.)

In reply to:
but I still don't see any real advantage over existing systems. I think that for most cases the redundancy is overkill. Maybe if you're in serious rockfall terrain.
It's a handy item--the "dental floss"--, and it I think will
show noticeably better equalization. I'll try to show some
pure-cordage implementation, too. The extension limiting
is quite nice. Craig Connally shows a sling w/limiter knots
(overhands) in which one clips just a single strand,
and thus has this triangular capture space. I think that
folks will prefer some presence of back-up. Again, that ADT
won't have ADT effects (except in the wild case that the
main sling fails while anchors hold); but it is kinda awkward
--just an idea of a safety for one implementation.

In reply to:
orange and white sling twice instead of adding the American triangle.
One could. A small matter then might be the bunching of
the connection eyes w/both slings active (but one could tie
them into different sizes--longer/shorter eyes).

In reply to:
If you want redundancy for that sling breaking why back it up with an inferior system?
Qua back-up--i.e., one anchor failed--, it is NOT the inferior
ADT you point to: no longe any triangle, just a loop.
But your suggestion above is good, fine. Again, the main
point is the general structure/shape.

In reply to:
I prefer something like this ...

Here I'll remark also re Aric's implementation: you are leaving
the connecting strand(s) needlessly SLACK, and that
lengthens extension.

*kN*


hafilax


Feb 23, 2009, 6:41 PM
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kN, thanks for the hint. I found the BD site and it echos the Mammut study. The slings mostly broke at around 50% of their rated strength (~11kN) and I agree that that is plenty strong. It's interesting that the nylon slings broke in the static pulls and that the spectra slings broke in the drop tests showing that the dynamics are important. I will still avoid hitching slings together.

The experiment that I am most interested to see is something that explores rope dynamics. What is the Hook's law regime? Is the damping critical? What are the recovery dynamics? How does all of that go into shock loading and zippering?

It would be nice to understand what end of the compromise between extension and equalization we should be leaning toward and when we should be employing the creative anchor setups that people have been coming up with.

I've been imagining some setups that could look at this but it's hard to describe in text. Maybe I'll draw something up if I'm bored one day.


JimTitt


Feb 24, 2009, 5:13 AM
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In reply to:
The experiment that I am most interested to see is something that explores rope dynamics. What is the Hook's law regime? Is the damping critical? What are the recovery dynamics? How does all of that go into shock loading and zippering?

This has been studied to death already!

The easiest start into the topic is going to be "Measurement of Dynamic Rope System Stiffness in a Sequential Failure for Lead Climbing Falls" by Beverly/Attaway.

For the damping effect in ropes then Martyn Pavier is your man:- Martyn Pavier, (1999) Experimental and
theoretical simulations of climbing falls. Sports
Engineering, Volume 1, Issue 2, Page 79-91
and "Derivation of a rope behaviour model for the analysis of forces developed during a rock climbing leader fall". The Engineering of Sport 1. 1996

And for how this is integrated into systems:-
"An Estimation of the Load Rate Imparted to a Climbing Anchor During Fall arrest". D. Custer
and
"Forces Generated in a Climbing Rope During a Fall" A. Philips, J Vogwell & A Bramley, both in The Engineering of Sport 6

There are others, notably from the Italians and some interesting stuff from Japan.

None of which appears to have any relevance to tying loads of bits of string together in fancy ways and hanging an inattentive fat slob with a belay plate on it!

Jim


hafilax


Feb 24, 2009, 11:17 AM
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Thanks for the articles. I guess I should do a journal search before speculating on what needs to be studied. Blush

I was going on assumptions based on what I have read here and largely on rgold's posts. The studies you've cited seem to centre around low fall factors and a fixed spacing between a pulled piece and the next one. The conclusion from the paper is that the rope mostly recovers between the piece pulling and landing on the next.

Is it possible to put pieces close enough together that this doesn't happen? This would be the situation of extension at an achor. People are still designing systems that minimize extension and I really want to know if this is needed and safer. Is a sliding-X as safe as the ELETs here?

I think that instead of pulling a bunch of anchors that select from the continuum of possibilities that it would be more instructive to do an intense study of rope dynamics and especially the recovery time.

Pavier's model is really quite close considering but even he admits that there are significant non-linearities. The paper cited only gives one sample plot so I'm sure he's done multiple lengths and fall factors and it would be interesting to see if the spring constant is roughly proportional to length like theorized and what happens at higher forces. The greatest non-linearities seem to be on the recovery side.

Basically what I'm saying is that yes it has been studied to death but I think there's room for more.


JimTitt


Feb 25, 2009, 8:30 AM
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As it happens I canīt see that it makes any difference which way it is set up because you cannot control the global parameters in any way and potentially one can be at the extremes of these, which would change what is desirable.
The failure mode of the gear can either be instantaneous, removing no energy from the system OR it could be a progressive rip through removing 99% of the energy.
The belaying can be very soft removing 99% of the energy or it can be hard, removing none.
In real life you can never guarantee for example, that the rope will not hang up on something turning ones anticipated soft hold into a solid hit.

In the sequential failure study they used a blocked rope, giving an extremely hard stop and a failure system that removed a considerable amount of energy whereas with a normal belay plate the results would have been completely different, in fact they would have probably never achieved runner failure.

Itīs going to be a complicated test to do, taking into account fall factor, fall length, belay force and varying gear failure modes!

Personally I never use powerpoints, equalettes and all that stuff anyway and never intend to.

Jim


knudenoggin


Feb 25, 2009, 1:06 PM
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adatesman wrote:
Looks like I only pulled it to 5kn, but with only one loop of the powerpoint and one leg leg connected.
This is what puzzles me about your set-up: the 'biner should run
on a twin-strand section, not a single strand, given the way
you have tied off the gold&white sling. (If one ties a sling with
Overhands at the anchor-connection corners, that is presumably
to provide for clipping into with separate anchor legs. E.g., in
the 4-anchor'd Equalette shown above, the anchors are close
enough (leftmost/rightmost pairs, resp.) that each could have
such a pig-tailed sling feeding a single connection to a lower
powerpoint ELET.) If one is employing cordelette cordage,
then tying to a folded/doubled HMPE sling makes sense,
and the cordage will provide the 3rd, "connecting" side,
non-redundantly.

In reply to:
And remember, the knots joining the runners are essentially Eskimo bowlines and rather strong ...
I say not: my current thinking is that it's better to tie from the
anchor into the (doubled/folded) sling with a SheetBend (Becket
Hitch) --possibly a clever variant-- and thus have Sheet bend
dynamics w/o failure, and Bowline ones with opp. side failed;
and then Lapp bend if this side fails. Because I'm less enthusiastic
re the Eskimo Bowline (which would be taking 100% load, vice the
Bowline (= Bowline on a bight, both ends loaded); in the 1st & 3rd
cases, the line is taking just 50% of the load at the knot).

But here we have somewhat unknown circumstances, so we'll
believe it when we see it tested! Esp. of interest is behavior
--i.p., signs of frictional heating/melting of HMPE sling--
on dynamic loading. And for that, drop tests need only deliver
significant loading--i.e., one need not insist on breakage. I.e.,
one could do a few FF 0.5 .. 1.0 drops, checking for effects;
some full UIAA drop of course is wanted for full assurance.

In reply to:
... with only 1 of the 2 loops clipped and pulled to 1129 lb-f (~5kN). There was some creep in the knots (as shown by the blue threads no longer being tight up against the knots), but far less than I expected.

And, again, BOTH sliding-span legs should bear load, which should
reduce slippage of them to nil. Now, on 1-arm failure, the knot's
loading suggests that one strand will be less tight than the other
(or have more to *give*), so it will be of interest to see what
occurs in a drop.

*kN*


knudenoggin


Feb 27, 2009, 10:39 PM
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In reply to:
ELET ::= Extension-Limiting Equalization Triangle

The ELET is a general schema. Its essence is the containment
of the powerponit connector, and the limited extension if one side
fails. How it gets implemented will vary on circumstances per user.
...
There are also clever ways of implementing the entire thing in cord.

Voici!
The images below present an ELET implemented with 8mm low-elongation
kernmantle. The particular knotting only occurred to be as I was
preparing to tie another knotting by using 3 different cords so as
to highlight particular parts; but this knotting was figured out then
--just in the nick of time, one might say (sparing all the hassle of
arranging the different cord segments).
.:. Laziness, another Mother of Invention?

The easiest way to implement an ELET is probably using cord for
attaching to the anchors and an HMPE 24" sling for getting low
friction for the powerpoint connector; and this structure would be
built by clipping a bight of the cord into one anchor, sizing the
first arm length to then tie off to one end of the sling (which
need not be knotted itself--no Overhand loops, i.e.), then tie
the connecting span to the other end of the sling, and
finish by reaching through the 2nd anchor and joining the sling
ends with a bend.

But there's a pretty simple way to effect an ELET using only
cord. In the sequence of photos linked, the ELET is to have
begun with the right leg, tying a Bowline on a Bight so that
one eye is sized to be the connecting side, and the other "eye"
is the two ends; the standing part is an appropriately sized
bight to be clipped first (after tying the knot, though).

Then the ends are sized for the sliding spans /powerpoint,
and tie an Overhand through the short eye of the BoaBight
(which roughly makes Ashley's #1029, which in one of his
many books Budworth named "Tricorn" eyeknot--it's a good
knot for the three possible loadings, it turns out). This leaves
the untied ends to finish connecting, to the 2nd anchor, to
be tied together for form the bight for that arm; I've used
a structure of an eyeknot that is nicely compact and should
be easily enough untied (one could use a bowlineque knot
here instead, or just join the ends together however).

*kN*

ELET in 8mm cord of Bwl-on-a-Bight / Tricorn EK (#1029) & Bollard EK-bend


http://www.postimage.org/image.php?v=aVoaHZA

http://www.postimage.org/image.php?v=PqoCsmi

http://www.postimage.org/image.php?v=aVodQ1S

http://www.postimage.org/image.php?v=aVofWer

also Quick Fig.8 eyeknot (white)"


(This post was edited by knudenoggin on Feb 28, 2009, 5:16 PM)


knudenoggin


Mar 2, 2009, 10:43 AM
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In reply to:
[re use of HMPE slings] ... but I still don't see any real advantage over existing systems.

As shown, the ELET can come in different flavors, per taste.
But here is a slightly edited quote from Craig Connally, who presents
one simple ELET in his book, The Mountaineering Handbook (p.148),
reporting on his then recent quick-test of frictional differences
between materials & structures. This was my motivation to put the
HMPE sling in the powerpoint, with twin cord tying it off to anchors.

In reply to:
Warnings: Me [CraigC.]: my academic and professional careers have involved making, analyzing, and reporting sensitive scientific and engineering measurements, and I'm acquainted with the stick/slip and slide rate issues when measuring friction. I didn't do drop tests or attempt any kind of abrupt loading[--]I didn't attempt to simulate fall forces. What I did was make a number of 2-placement anchors in a consistent geometry using a variety of materials, hang a heavy weight at the master point, and use an accurate spring scale to measure the force required to pull the master point sideways through its equilibrium position (referring to this force as indicative of friction , in this discussion). I didn't make enough measurements to do statistical studies (no standard deviation, no chi squared tests, none of that), but if I had to guess I'd say the standard error would be maybe 20%. No observations were earthshaking or inexplicable. If these warnings make you think such measurements would be useless, not germane to this thread, or misleading, now would be a good time to stop reading.

Otherwise, here's what I observed.
I set up 3 different anchor designs: the Sliding-X , the 2-anchor Equalette , and the "[ELET ]".

[..]

* Normalizing to the sliding friction of the Sliding-X , I measured the sliding friction of the Equalette to be about half that. The sliding friction of the ELET measured about half that of the Equalette (1/4 that of the Sliding-X), which is what you'd expect just by looking at their designs. This was true will all the soft materials I tested. These observations refer to an equalette without limiter knots. Tying limiter knots in the Equalette decreases the measured sliding friction. I interpret this to reflect the difficulty of tying limiter knots that create perfectly equal length strands between them (in their final position as they support the carabiners, necessary for perfect force balance at the master point) and perhaps to irregular orientation possibilities of the two identical lockers. This is another illustration of the dictum already brought out, that perfect equalization requires cord/webbing slip around the anchoring carabiner and that limiter knots prevent this. I didn't test it, but likely a Sliding-X with limiter knots would have the same issue. In other words, limiter knots tend to make the Equalette perform more like an ELET, which is good in terms of reducing sliding friction but not in terms of balancing the loads on the two strands.
* I could not resolve a difference in the sliding friction of 11/16 (18 mm) climb spec webbing and 7 mm accessory cord, in any of the anchor configurations.
* There appeared to be a reduction in sliding friction going from 7 mm cord, to 6 mm cord, to 5.5 mm Tech Cord, but the effect, if there, was small in all 3 configurations.
* I measured a significant decrease in sliding friction using Spectra/Dyneema webbing, compared to nylon. The difference was almost a factor of 2, meaning that a Sliding-X with HMPE (Spectra/Dyneema) webbing would perform almost the same as an Equalette made with 11/16 nylon webbing or 7 mm cord. I question whether limiter knots or hitches tied in HMPE material would hold satisfactorily.
* I could not resolve a difference in the sliding friction in any anchor design between ordinary 1/2" Spectra/Dyneema webbing and a Mammut 8 mm Dyneema dental floss sling.
* I did notice an improvement in sliding friction when using a "wide mouth anodized pear biner," compared to non-anodized HMS/pear lockers (which had apparently larger rope bearing radii), but I tested this only with the Sliding-X and ELET because I didn't have two matching anodized HMS/pear biners with their anodizing intact. While the effect was noticeable, it was near the resolution limit of my testing.
* Presumably, lower sliding friction is better, because that will allow better balancing of forces during the instant of peak fall force, thus better achieving the design objectives of the anchor, but applying these observations to or making conclusions about any anchor design when impacted by real fall forces is outside the scope of my inquiry this weekend.

RC.com source URLink for this quote is
http://www.rockclimbing.com/..._view=&start=705
--post #705 (SEVEN HUNDRED five, yes(!), and far from the last!!)

*kN*


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