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Belay Anchor Load Distribution

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 Oceanic 17 Apr 2011
Okay, so I understand that the use of a cordelette belay set up, with different length legs, can result in all the load being transferred to just one of the three bits of gear used to create the belay.

My understanding of how this happens is that the shortest (most inelastic) leg reaches it's limit of stretch first, while the other two legs are only stretched to a proportion of their maximun stretch, and therefore less load is transferred through these partially stretched legs.

Question 1 - Is what I just described correct?

Question 2 - Can anyone explain why everything I've just described does not apply to an anchor formed from dynamic climbing rope, with different length 'legs'?

 iforwms 17 Apr 2011
In reply to Oceanic: Yes. And it does apply when using a dynamic rope. Possibly to a slightly lesser extent as the tope will stretch more and equalise slightly better.

Anyone feel free to correct me if I'm wrong...
In reply to Oceanic: a dynamic rope of length x has the same stretch % of the same rope with a length y but the actual length of stretch in each length will be completely different.

For dyneema the stretch % is much less than dynamic rope so its less of an issue to have two completely different lengths of a 2/3 arm belay setup I would have thought. to be honest you don't always have the privilige of choosing your anchors when you are on a route. you get what your given and I wouldn't think twice about having two different length anchors.
OP Oceanic 18 Apr 2011
In reply to Oceanic:

Any of the Monday morning crowd got an opinion?
 SCC 18 Apr 2011
In reply to Oceanic:

I was under the impression that it was the difficulty of getting all the pieces of gear equalised properly when setting up a cordelette, combined with the very very low amount of stretch that led to the problem of loading one piece of gear far more than others. I wasn't really aware that the length of the legs in a cordelette set up was a major factor.

It's far easier to equalisewhen using ropes - by that I mean it's easier to adjust the individual anchors to get better equalisation - than with a cordelette. This, combined with the advantages of dynamic rope as opposed to static sling/cord is why I thought it was preferable.

I'm not convinced how much of an issue the additional stretch in uneven length legs of a dynamic setup would cause.
I would suggest that this is pretty much negated by the fact that you can adjust the legs much more easily, and take some of the stretch out of the longer leg(s) until you feel that the anchors are loaded as evenly as you can make them?

Si
 AndyE9 18 Apr 2011
My understanding is that it has nothing to do with the amount of stretch in a given rope os sling.

It is that if you use your climbing rope or a sling even a number of slings or a mixture is that by equlising all "legs" it prevents shock loading to the system if a peace of gear should fail , if it has not been equlised and a bit of gear fails it can then shock load the system which could then cause for another bit of gear to fail..

if each leg is not tied of or made as an individual leg of the system if a bit of gear fails then this can cause the wole system to pull through and even out..

There are a few exceptions tho , if you had and were using bomber placements , a sliding "X" config can be used , but by placing an over hand knot in each leg restricts the chance of heavy shock loading, but if one placment was to fail the system would be shock loaded. but the sliding "x" does allow for euqal distribution which is self adjusting over the whole system.. Tho I have only seen it used a few times..
 AndyE9 18 Apr 2011
youtube.com/watch?v=zDXvI18p140&


vid of sliding x if you were wondering
 CurlyStevo 18 Apr 2011
In reply to Oceanic:
The leg length makes very very little difference if the angles of the legs at the knot remain the same AS LONG AS you are using a low stretch sling like dyneema. Using a rope to equalise it's the stretch in the longer legs which causes the shorter legs to get loaded more.
 CurlyStevo 18 Apr 2011
In reply to AndyE9:
"My understanding is that it has nothing to do with the amount of stretch in a given rope os sling. "


you may find this article interesting then!
http://www.caves.org/section/vertical/nh/51/Multi-point%20pre-equal%20ancho...
 AndyE9 18 Apr 2011
The stretch from a dinamic rope used to build your belay would be very small unless each leg was m's long.

If each leg is kept within close range, the amount of stretch in each leg of the rope will not be an issue as long as you have equlised your system . The amount of dinamic reasponse in a few foot of rope is very small, and should not really be a factor..

 CurlyStevo 18 Apr 2011
In reply to AndyE9:
> The stretch from a dinamic rope used to build your belay would be very small unless each leg was m's long.
>
> If each leg is kept within close range, the amount of stretch in each leg of the rope will not be an issue as long as you have equlised your system . The amount of dinamic reasponse in a few foot of rope is very small, and should not really be a factor..

That wasn't the conclusion of the scientific study I linked above
OP Oceanic 18 Apr 2011
In reply to CurlyStevo:
> (In reply to Oceanic)
> The leg length makes very very little difference if the angles of the legs at the knot remain the same AS LONG AS you are using a low stretch sling like dyneema. Using a rope to equalise it's the stretch in the longer legs which causes the shorter legs to get loaded more.

www.outdoordads.org/advrock/ar09-anchors.ppt

The powerpoint presentation above has a picture (probably from John Long's book) on slide 15. It illustrates the effect of leg length on load distribution when using a cordelette.

(Tee hee! Kind of a powerpoint powerpoint slide).
 Mr Fuller 18 Apr 2011
In reply to Oceanic: There's been a lot of threads on this sort of thing recently, and it shows the amount of uncertainty around. There's been links to Gadd's blog, to journal articles, to independent research... and there's not really been conclusive opinions as to which method to use, and when.

Surely this should fall under the BMC's remit and they should offer advice on this?
 AndyE9 18 Apr 2011
In reply to CurlyStevo:
> (In reply to AndyE9)
> [...]
>
> That wasn't the conclusion of the scientific study I linked above


What I said was in the report ,but was worded diff ,

i said that by having shorter legs the dinamic respons will be minimal , the report states that having longer legs allows more stretch which inturn can unequlise the system..

this is just what I said !!

Your report just backs up what I was saying but is worded diff

 CurlyStevo 18 Apr 2011
In reply to Mr Fuller:
My personal conclusion is that belays will only very very rarely fail in the real world on good gear placements as long as you have obeyed the basics of angles between the pieces, keeping the belayer in line with fall, placing a piece soon after the belay to protect against a factor 2 etc.

So whilst it's good to know the results of the more resent work, I'd be more impressed by someone who can set up a belay that is strong enough and set up quickly than someone that over engineers the belay and takes ages to do it.
 henwardian 18 Apr 2011
In reply to Oceanic: I use the cordaleette method for making anchors. Quite often when I set up an anchor and start belaying I then notice that the ropes pull the anchor in a slightly different direction than anticipated and 1 or more legs are not as loaded as the other(s). A piece of gear that is 180 degrees to the direction of load will be loaded far more than a piece that is say 120 degrees to the load direction, even if equalisation is perfect. If you put a cam in your belay and the system is moving a bit as you belay, it will often move a bit in the crack. There are, in short, loads of different ways that the legs will be unequally weighted and frankly I don't think anyone short of a rope access tech using bolts builds an anchor that distributes precisely equal loads to every point (I guess you can get closer with the sliding X but I don't like it for at least 2 reasons*). None of this matters though because you should build every anchor so at least 2 pieces are absolutely bomber and even if one was to fail, the remains of the anchor could still take more load that you could ever put on it with a second falling off or the belayer dicking about. It is best if the belayer attaches to the cordelite with a short section of rope so any load they put on the anchor is damped by a bit of dynamic action from the rope, this will ensure any loading of the anchor by belayer or second has rope in the system to absorb shock.

If you are building a very marginal belay then the exact way you do it, with rope or cordelite, will depend very much on the placements you have at the time and possibly how well you think your bum is adhering to the rock you are sitting on!



* 1) If any piece fails, at least one other piece is shock loaded.
2) In my head, at the time of placement failure, the 'X' where the sling crosses itself moves very quickly while under considerable load. My knee jerk reaction is to not like nylon rubbing against other nylon under load and at speed. It's a gut feeling and I'm perfectly prepared for people to call me out on it.
 CurlyStevo 18 Apr 2011
In reply to AndyE9:
I've just reread your posts and I think either they were poorly worded or you haven't understood the report properly.

For example:
"The stretch from a dinamic rope used to build your belay would be very small unless each leg was m's long. "

"i said that by having shorter legs the dinamic respons will be minimal , the report states that having longer legs allows more stretch which inturn can unequlise the system.."

That certainly wasn't the conclusion of the report. They were more concerned with short legs. Common sense would tell me its the proportion of the length of the legs that will determine how much of a problem this will be, not that one leg has to be meters long

"My understanding is that it has nothing to do with the amount of stretch in a given rope os sling. "

I wasn't really sure what you were refering to here but the stretch of the legs in the belay set up obviously does have a large effect on the potential load on the anchors as the report describes.
 AndyE9 18 Apr 2011
there are other factors to think about if on multi pitch then the direction of force apllied to the system would load the system in a diff direction if the falling climber was above or below . . .

I like to have at least on bit of gear which is multi directional , or I will make adjustments to my belay once my second has joined me..

if you placeed all nuts with the direction of pull pulling down and your second climbs past you on the next pitch, he takes a fall the force can pull the belayer up , those nut which were bomber when pulling down have now just been pulled up they might not be so solid and may even pull out..

just something else to think about..
OP Oceanic 18 Apr 2011
In reply to Mr Fuller:
> (In reply to Oceanic) There's been a lot of threads on this sort of thing recently, and it shows the amount of uncertainty around.

I've just skim read the article that Curly Steveo has linked to, and my (admittedly hastily drawn) conclusion is that in some situations equalising a belay with a 16 foot Dyneema sling will distribute the load between the anchors more evenly than setting up a belay with dynamic rope. That's kind of a surprise when so many people put forward the 'rope is always safer' dictat.
 henwardian 18 Apr 2011
In reply to CurlyStevo:
> placing a piece soon after the belay to protect against a factor 2

I might go one further and say that it is best if you can place a high runner while still clipped to the belay before starting off and totally negate the chance of a factor 2 fall. I took a small factor 2 fall not so long ago and mangled my belayers hand which I felt quite bad about afterwards.
 CurlyStevo 18 Apr 2011
In reply to henwardian:
" A piece of gear that is 180 degrees to the direction of load will be loaded far more than a piece that is say 120 degrees to the load direction"

I think you mean the angle between the widest apart anchors here right? Even then depending on the other anchors and the material used to equalise, the widest apart anchors may not get loaded much at all (imagine a very good anchor in direction line of the fall and two anchors in line with this, 180 degrees apart equalised with a very low stretch material. As long as the central anchor holds the outer anchors will not recieve much load atall.
 gear boy 18 Apr 2011
In reply to: If the BMC/MLTA etc were overly concerned about this then would it not be the case that you would not use static rope in the the set-up of bottom roping and abseil systems?
 henwardian 18 Apr 2011
In reply to CurlyStevo:
> Ahem a piece 180 degress to the load direction will either not get loaded atall or will not remain at 180 degrees to the load direction. I think you mean the angle between the widest apart anchors. Even then depending on the other anchors and the material used to equalise, the widest apart anchors may not get loaded much at all (imagine a very good anchor in direction line of the fall and two anchors in line with this, 180 degrees apart equalised with a very low stretch material. As long as the central anchor holds the outer anchors will not recieve much load atall.

You misunderstand me. When I say 180 degrees, I mean that a piece of gear is directly in line with load, e.g. The piece of gear is at the top left corner of your screen, the central point of the anchor is at the bottom left corner of your screen and the second is directly below this on a rope. In this case the gear at 120 degrees is maybe placed somewhere like top centre of your screen. I hope this explains it better.
Your example seems to be based on gear that is at 90 degrees to the direction of load.
 CurlyStevo 18 Apr 2011
In reply to henwardian:
ahh OK I see what you meant
 Richard Wilson 18 Apr 2011
Does anyone use the equalette or even a quad in preference to the cordalette?
OP Oceanic 18 Apr 2011
In reply to Richard Wilson:
> Does anyone use the equalette or even a quad in preference to the cordalette?

I've used an equalette set up two or three times, I might start using one more now.

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