Friday, November 26, 2010

Triaxal Loading on Trees

Surprisingly, there is one mistake that both beginners and advanced climbers alike tend to make. Many people will wrap a tree with a sling and then clip the sling. Often the sling is wrapped around the tree in such a way that it is loading the carabiner improperly. A carabiner that is loaded from three directions is often referred to as being triaxally or tri-directionally loaded. This is very very bad...

In this photo the carabiner is radically tri-loaded.
An impact on such a carabiner could cause failure.

A tri-loaded carabiner is crossloaded. It will not hold a high impact fall. As such, it is important to use slings that are long enough to tie off. In the preceding example, there is not enough sling material to get all the way around the tree, but even if there was enough for the carabiner to hang more loosely, it could still triaxally load it.

One could tie the sling off with a pre-equalized knot, but this isn't required. The following photo shows one quick example of a tie-off that eliminates the possibility of triaxal loading.

Triaxal loading is a detail that a lot of climbers don't think about. But it is just these kinds of minor details that can get you in the end. The phrase, "the Devil's in the details," didn't come from nowhere.

--Jason D. Martin


Anonymous said...

What about girth-hitching the tree?

Michael said...

Would tri-axial loading still be an issue with a significantly longer sling around the tree?

Anonymous said...

How was the sling tied off in the second photo? I don't recognize this knot/tie off. Could you provide more detail on how to do this? Thanks.

American Alpine Institute said...

To answer each of your questions--

1) You certainly could girth-hitch the tree. But remember that if you set the girth-hitch in such a way that it is tightening on the tree, you create a pully effect, putting more force on the tree and on the sling. If you elect to girth-hitch, it's best to make sure that the sling is set-up so that it doesn't torque the tree more tightly.

2) As for the length of the sling...certainly a long sling could be used to mitigate this problem. For example, if you used a triple-length sling on the tree in the picture, you wouldn't have to tie it off. The two ends of the sling would not be pulling on the carabiner in a detrimental way.

That said, the photo in the picture is exagerated so that you can really see the tri-load. In real life, tri-loads aren't so exagerated. They're something that you have to carefully look for.

3) Number three guy, I bet you do know this tie-off... It's essentially the first part of the knot that you probably use to tie your shoes. It is not a closed or finished knot. Instead, it simply orients the force in the proper direction.

Great questions guys!!!!


Anonymous said...

Thanks for answering, great post!

Anonymous said...

Thanks for clearing that up. I figured it was a simple knot. Just wanted to be sure.

Keep up the excellent posts!