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triaxial loading at the power point: a cause for concern?
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glockaroo


Sep 2, 2002, 8:42 AM
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triaxial loading at the power point: a cause for concern?
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We've all seen belay/bivy setups where a big locker is clipped into the powerpoint of a cordelette and then multiple biners are clipped into that big locker.

I remember long ago hearing that loading a biner in a triaxial fashion compromises the biner's strength. I have never seen data as to the degree of strength reduction.

My only "evidence" is that I have seen Chris Harmston of BD write that triaxial loading is a "definite no-no" for biners.

So I ask: is loading up a powerpoint locker with varying force vectors at the belay risking some biner failure? Consider a worst-case scenario where you have big haulbag loads, multiple climbers and a potential factor-2 lead fall onto the anchor. I'm certainly not worried about the multiaxial load imposed by clipping my big-wall feather duster to the powerpoint.

Note that I am just asking the question. I have not arrived at a conclusion and I am not preaching at anybody.

A fix would be to insert a clippable link between the powerpoint biner and the sub-loads that can handle multiaxial loads. Perhaps one of those aluminum SMC rap rings. They are light, compact, seamless (no welds) and are rated to about 3500 lbf. If you're paranoid, use 2 in parallel. There are many rescue products that address this very issue but they are typically heavy and bulky.

So, what say ye? Anybody got data on this?


fishypete


Sep 3, 2002, 1:01 AM
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triaxial loading at the power point: a cause for concern? [In reply to]
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No data to add, just an observation, and some "educated" guesses.

When I am aiding (and hauling etc i.e. with several biners in the powerpoint) I always make sure I use one of my BIG pear biners with the big, deep curve (i.e. the opposite of flat-tops, more on that later) as the powerpoint.

Even when I have multiple things clipped into it, they are still all pointing almost exactly downward - thus the tri-axial loading is minimal at worst.

Obviously when the situation arises (as I guess it probably will eventually) where I see that things are pulling at significantly different directions, then a second powerpoint locker through the cordelettes may be a way around the problem. (Do you think this is a reasonable alternative to the aluminium links you mentioned?)

So for me, I haven't yet come across the tri-axial situation, given that all the loads are quite parallel.

Now just a few thoughts on the data side of things.

I think it would be very dependent on the specific biner. For example, the powerpoint biners I chose and large pears, and importantly have a very pronounced/deep curve (the opposite of the flat-top pear biners which are good for use with a munter hitch).

This means that all biners clipped into the powerpoint stay close to each other, tight up against the spine of the biner, and wont slide out of the deep curve (toward the gate) until the anglge they are pulled at exceeds around 30 degrees from the "longest" axis of the biner.

Thus, in the case where two transients are in the powerpoint, with loading directions divergent by up to 50 degrees (i.e. 25 degrees either side of the longest axis) there will be no biner shift.

As long as the biners dont slide, the "horizontal" vector created by the 50 degree angle will be trasmitted almost completely into the section of the powerpoint biner between the two transients, placing it in tension, a direction in which it is amply strong (I have only seen biners break on the gate side, generally by tearing off the tooth that the gate holds).

So in summary, it appears to me that as long as there is no biner shift i.e. the transients stay close to each other and the spine of the powerpoint biner, the triaxial or horizontal loading component would be transferred only into the curve of the powerpoint placing it in tension - not a large problem.

The problem I do see is when the biners slide toward the gate side, or when there are too many biners in the powerpoint such that they occupy much of the pear end of the powerpoint. I see this as being quite dangerous, and personally only ever put 2 biners that may experience significant weights/falls into a powerpoint (I often end up with 2 powerpoints).

This is actually the second reason why I like my powerpoints with the large, deep curve. Unlike the more flat-top biners, these hooked ones will actually accept two transients, which when loaded, actually sit almost exactly either side of the longest axis of the biner (flat-top biners and non-lockers such as those on quickdraws can only fit one biner in the optimal position right along the longest axis. Others are forced progressively off toward the gate). This means that I can put two biners in my powerpoints and weight them along the same axis as the biner was tested, thus the failure load should be as quoted.

Glock, have you had situations where widely diverging angles have been a problem? I would be curious to hear.

And so what is the moral of my story?

Personally, I only use powerpoint biners that have the deepest curve or hook I can find, thus keeping all the transients as far away from the gate side as possible. As long as they remain close to each other and dont slide, I think the tension in the hook resulting from diverging loading angles would not be a problem.

Cheers

Fishy.




[ This Message was edited by: fishypete on 2002-09-03 02:32 ]


ergophobe


Sep 3, 2002, 12:28 PM
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triaxial loading at the power point: a cause for concern? [In reply to]
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No specific data, but years ago I broke a lot of slings and biners at Climb High. These were mostly new slings (sewn and knotted) and biners that we were batch testing, but I also brought in a variety of finder biners and such.

Basically, the biners almost always break at the nose. Sometimes lockers way exceed their rated strength because the ferule gives support to the nose.

That being so, anything that moves the load toward the nose will mean that the biner can sustain a smaller load. This is regardless of the geometry of the biner, but it should be clear that proportionally when you move 1cm toward the nose on a Neutrino and 1cm toward the nose on a large HMS biner, the Neutrino will take a bigger performance hit (all other things being equal, but of course the angle of pull and other things will affect the actual performance).

You can see noticeable differences in several situations other than the one you mention. For example, if you tie in with a clove hitch instead of a figure-eight you push the load slightly toward the nose. Similarly, if you have a doubled sling and you lengthen it but leave the twist in, you will move the load slightly toward the nose.

As a general rule, the situations that I mention have relatively small effects, but I think it's worth keeping in mind if tying in to a small biner with a clove hitch on a thick rope.

If you start adding lots of biners and there's not enough freedom in the system for the loaded biner to slide toward the spine (for example if those closer to the spine are loaded), then you probably will lose significant strength. If you compound this by loading the biner at an angle which pulls out on the nose, that will add to the problem and I think that's a lot easier to achieve if you have a huge pig hanging from the biner.

Conclusion - try to keep loads as close as possible to the spine of the biner and in the axis of the spine, especially for non-lockers.

Sorry, no numbers since this was 14-15 years ago that I did this testing.

Tom


estwing


Sep 3, 2002, 12:50 PM
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triaxial loading at the power point: a cause for concern? [In reply to]
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This is totaly out of my league, but would a petzl or similar rigging plate be of any use in this situation?

Have a nice day.
Sam


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