Forums: Climbing Information: The Lab: Re: [BetaRock] Theory about forces in a 3-legged cordelette: Edit Log


Jun 25, 2012, 5:25 PM

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Re: [BetaRock] Theory about forces in a 3-legged cordelette
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BetaRock wrote:
First, I don't think John Long himself was involved in the Sterling tests to which I'm referring. Those tests were performed by Jim Ewing, R&D manager at Sterling Ropes. The statistics were completed by Dr. Lawrence Hamilton and Dr. Callie Rennison.

Second, according to the test summary, they did not perform tests for a 3-legged cordelette rig. Only the 2-legged.

Would you mind detailing the flaws in Ewing's tests? The details of the experiments are laid out in the book and determined that the load distribution across the two legs were dismal: almost 800 pounds difference between the legs in a Factor 1 fall.

This difference in force seems significant to me. Is there debate surrounding how they performed those experiments?

Only a little bit of debate Wink Laugh;so=ASC;mh=25;

The fourth post and many others are by John Long. As you can see John WAS involved in the tests.

I can't speak for all the details on John's tests but basic trigonometry ensures close to equal loading if you create a decent 'V' in a two leg anchor. It seems he aligned the pieces vertically so naturally equalisation is quite poor particularly with static cord.

Your 800pound difference is meaningless unless you give it as a percentage. I would consider 20%, 20%, 60% equalisation still adequate as far anchors go. The goal is more about redundancy rather than perfect equalisation.

John Long was also incorrect in his conclusion that shock loading doesn't matter. It very much matters if there is a load at the anchor such as in a direct belay or a hanging belay.

(This post was edited by patto on Jun 25, 2012, 5:32 PM)

Edit Log:
Post edited by patto () on Jun 25, 2012, 5:32 PM

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