Load cell testing: How much force does a bounce test produce

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20_kN

Sport climber

20 kN Land

Topic Author's Original Post - Jun 12, 2012 - 11:29pm PT

After reading the thread from Axledavis about bounce testing, I got a bit curious as to how much force a bounce test in the real world actually produces. Two members in that thread said they bounced around in a sling, or dropped a weight in a sling, and got an impact force of around 4 kN. That seemed excessively high to me, especially considering Metolius quotes a hard bounce test at 2 kN. So I decided to replicate real-world aid bounce tests and see how much force they produce. This testing is non-conclusive; it is simply for fun. It is, more or less, a test of how much force I will inflict on pieces I test, rather than an absolute statement regarding bounce testing forces.

The point of this thread was to be as real world as possible. So I conducted this test in Yosemite, on an aid route, on aid placements (an A0 bolt ladder). I conducted the tests using all the gear I normally use on a wall, and in the exact manner I would test a placement on a wall. In every case, I tested the placement quite aggressively – I didn’t hold back.

-I used a 5,000 lb load cell with a rated accuracy of .02%, and a computer driven strain gauge analyzer that sampled the load cell at 500Hz.

-I weigh 158 lbs

-On the tests I was wearing a rack, the rack weighed 17.5 lbs

-I was using Yates adjustable daisy chains (nylon)

-I was using Metolius wall step 8-step aiders

(1) I conducted six different tests. The first set shows an aider bounce test versus a daisy bounce test, but without a rack.
(2) The second set is the same as the first, but with a [nearly] full El Cap clean aid rack (which weighs 17.5 lbs).
(3) The last set was an absolute worst possible case scenario where I was hanging only from the load cell and no part of my body was touching the lower piece. The first test in the series showed an aggressive daisy test. The second test shows an excessively aggressive daisy test where I was literally slamming myself down onto my daisy as hard as possible. This test was more aggressive than any bounce test I would use on a wall. I was wearing the rack in both tests in this series.

The absolute highest force incurred on the top piece occurred during the last test (the excessively aggressive test,) and racked in 681 lbf. or 3.03 kN. However, that test was synthetically extreme. The highest force incurred during a realistic aggressive bounce test was 643 lbf. or 2.86 kN. But again, I was hanging solely from the piece which is not realistic in a wall climbing scenario. So the highest force incurred using an aggressive daisy bounce test that is realistic to a wall climbing scenario is 618 lbf. or 2.75 kN.

So my testing seems to imply that a hard bounce test in your aiders will produce 400-550 lbf and a hard bounce test directly on your daisy chains will produce 500-600 lbf. I find it unlikely that I would be able to produce a higher impact force using conventional nylon pocketed daisy chains simply because I was bouncing around hard enough that if I were fified into a pocketed daisy, the aggressive bouncing would likely result in the fifi coming out of the pocket. However, it is possible that using a Dyneema daisy chain would result in a higher impact force; maybe I can test that in the future.

Swami Jr.

Trad climber

Bath, NY

Jun 12, 2012 - 11:43pm PT

don't listen to the moron who posted prior, good work. Thanks for the post.

Norwegian

Trad climber

Placerville, California

Jun 12, 2012 - 11:48pm PT

i wanna see a load test
quantifying the surge upon
aggressively versus
overly aggressively bang a girlfriend.

Mark Hudon

Trad climber

Hood River, OR

Jun 13, 2012 - 01:33am PT

Interesting, thanks.

Wade Icey

Trad climber

www.alohashirtrescue.com

Jun 13, 2012 - 03:24am PT

swan slab?

I've never bounce tested a bolt...what are the numbers for a blue brass hb?

20_kN

Sport climber

20 kN Land

Topic Author's Reply - Jun 13, 2012 - 03:53am PT

Mark, when did you get down from GR/Muir?

duncan

climber

London, UK

Jun 13, 2012 - 04:37am PT

Thank you for taking the time to do these tests and report them. So aggressive bounce-testing generates the equivalent of about x3.5 bodyweight. That seems to provide some margin on a well-tested placement.

There are other tests results that I'd be interested in, perhaps they have been reported already but I'm not aware of it:

1. How much force is generated when you move up on a piece. Is this markedly higher than bodyweight?
2. How much force can you generate manually, e.g. when seating a wire? Jim Titt suggests not more than bodyweight (assuming he weighs more than ~58kg!) before the process becomes too painful. This would be interesting and possibly reassuring (or not!) for those pant-filling occasions when you have to load a piece without a proper bounce-test: on traverses, moving from free to aid, or lowering-off after a run-out.