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27-Feb-2015 10:55:23 AM
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Trying to find out just how weak a crab is made by triaxal loading.
see this link for some explanation (http://blog.alpineinstitute.com/2010/11/triaxal-loading-on-trees.html
I have set many an anchor up that have a degree of loading in this way, a diagonal pull at least, especially when its a top rope with three natural anchors. Normally two crabs used then at the main fulcrum point.
Another link is here http://outdoors.stackexchange.com/questions/1384/what-does-it-mean-to-cross-load-a-carabiner
which shows the straight through and cross loading issues.
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27-Feb-2015 11:03:50 AM
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That first link is broken...get rid of the dot on the end of - html.
Strength is reduced dramatically. Have spare slings and it can always be avoided. In a top rope situation you could use an over rated steel crab to get around it.
On 27/02/2015 tooclimb wrote:
>Trying to find out just how weak a crab is made by triaxal loading.
How long is a piece of string?
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27-Feb-2015 11:09:16 AM
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27-Feb-2015 12:10:21 PM
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Thanks
That pic shows the various strengths that each protection point has at various angles. That is not what I am after and I appreciate all that. I wouldn't think that you can transfer that logic to a crab, because it will depend on the rating of the crab.
I'm not seeking ways to solve triaxial loading but knowledge on the crab strength. For instance we have a standard kong crab, 27kn vertical & 9 kn cross. Whats its diagonal (ie 30 deg) strength. Surly the "big" end is not just designed for just one rope?
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27-Feb-2015 12:19:10 PM
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It should be noted that multiplication of forces when you have two anchors that oppose each other to a degree (as in the diagram above) is far from the only reason why tri-axial loading is bad. You still get that multiplication of forces on the anchors even if you avoid it by knotting your slings before clipping them to the carabiner in question.
The main problem is that HMS and D-shaped carabiner are designed so that whatever is attached to each end of the carabiner gets pushed right up against the spine, which means the spine takes most of the load and the gate side takes very little, allowing manufacturers to avoid having to make the gate as strong as the spine, which would be difficult and/or result in a heavy carabiner. When you tri-axially load a carabiner, you are forcing one of the loads into the corner on the gate side, so that the gate side takes more of the load than the carabiner was designed for. It also adds an element of cross-loading, because of the two anchors pulling against each other along the shortest side of the carabiner.
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27-Feb-2015 12:27:45 PM
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This is a very complex question to answer and is highly affected by the geometry of the carabiner, the gate mechanism and the width of the attached slings/rope. Cross loading failures can be generated at 90 degrees at surprisingly low forces (have a couple of steel gates with these types of failures from testing in my office). In summary ... there is no simple answer.
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27-Feb-2015 12:41:41 PM
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yep all good thanks - so Im after an idea of the strength when two ropes are pulling on that big end at an angle of around the 30deg, which would be a normal belay configuration.
In the pic what sort of kn can we expect from crab at the blue rope?
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27-Feb-2015 12:47:07 PM
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thanks - it seems so. In the pic I uploaded such would seem a typical situation. You would think there would be some technical information seeing it is normal.
I couldn't find any hence my questions here.
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27-Feb-2015 12:52:10 PM
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On 27/02/2015 tooclimb wrote:
>yep all good thanks - so Im after an idea of the strength when two ropes
>are pulling on that big end at an angle of around the 30deg, which would
>be a normal belay configuration.
>In the pic what sort of kn can we expect from crab at the blue rope?
You really can't know how much force the blue rope could impart before the krab breaks. If manufacturers won't specify it I 'm certainly not going to guess.
I'd question whether this is a "normal" belay setup. I'd hesitate to clip 2 clove hitches into the one crab.
Is there a particular scenario you're looking at or just curiousity?.
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27-Feb-2015 1:16:20 PM
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Could be a top rope setup, the two ropes could be two slings, whatever. Invariably in the past I have always had two ropes in the fulcrum crab(s) on top rope, and if natural anchors, coming form three substantial protections.
Ive read a couple of things on it to make me think this coaxial loading may be serious although personally I don't think so or I would probably have been injured by now.
just curiosity
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27-Feb-2015 1:18:46 PM
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On 27/02/2015 tooclimb wrote:
>thanks - it seems so. In the pic I uploaded such would seem a typical situation.
>You would think there would be some technical information seeing it is
>normal.
No, it's not normal, nor is the pic typical.
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27-Feb-2015 1:40:42 PM
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Sign up to RopeLab and you can read the test report "three-way loading of carabiners".
Exactly what you are asking about.
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27-Feb-2015 1:48:43 PM
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normal and typical re this thread with regard to two ropes or slings or whatever loading the binner.
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27-Feb-2015 1:49:49 PM
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Thanks re rope lab
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27-Feb-2015 1:52:26 PM
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On 27/02/2015 tooclimb wrote:
>Could be a top rope setup, the two ropes could be two slings, whatever.
>Invariably in the past I have always had two ropes in the fulcrum crab(s)
>on top rope, and if natural anchors, coming form three substantial protections.
>Ive read a couple of things on it to make me think this coaxial loading
>may be serious although personally I don't think so or I would probably
>have been injured by now.
>just curiosity
>
Yes it is serious and just because you haven't been hurt doesn't mean it isn't.
Sometimes we have to break the rules because we don't have alternatives but it doesn't make sense to deliberately rig something wrong when you have the time and equipment to do it right,
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27-Feb-2015 2:15:18 PM
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yep for sure. Its not so difficult to solve in that using two opposed binners would seem to work ok.
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27-Feb-2015 2:15:25 PM
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In the situation in the image, I would use two carabiners, one for each clove hitch.
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27-Feb-2015 2:24:36 PM
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yep I agree. The consensus is then that it is potential dangerous to coaxial load although there is still no rating data, Don't think I'll join that web site that was suggested at the moment for the $60 but thanks anyway
I suppose there is a thread on belay set ups somewhere or maybe a new thread on belays or continue here if you want to discuss my sweet looking clove hitches.
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27-Feb-2015 3:25:18 PM
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On 27/02/2015 tooclimb wrote:
>yep I agree. The consensus is then that it is potential dangerous to coaxial
>load although there is still no rating data, Don't think I'll join that
>web site that was suggested at the moment for the $60 but thanks anyway
Fair enough, but $60/year for Richard Delaney's work is worth every penny.
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27-Feb-2015 3:35:59 PM
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On 27/02/2015 tooclimb wrote:
>>yep I agree. The consensus is then that it is potential dangerous to
>coaxial
>>load although there is still no rating data, Don't think I'll join that
>>web site that was suggested at the moment for the $60 but thanks anyway
Go on, $60 bucks and you'll get rating data, or rather a de-rating % recommendation based on destruction tests of 34 carabiners with various angle loading by a qualified engineer. Plus there is a heap of other great stuff there and you can ask questions: I asked about using a cats paw knot to shorten a sling and Richard ran tests to give a definitive answer — no. $60 might have saved my life.
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