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Bounce testing and impact forces
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jcain


Jul 9, 2004, 8:04 PM
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Bounce testing and impact forces
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I heard an aid climber say that if you agressively bounce test your placements you can be fairly confident that earlier placements will hold if the current one fails. I am new to aid climbing so I don't have any experience with which to judge his remark.

I found his remark hard to believe, but after doing some research I can now see his point.

Using the impact force calculator at www.myoan.net/climbart/climbforcecal.html, I entered a weight of 180#, a rope length of .16667 feet (two inches) and a distance also of .16667 feet. I clicked the static rope indicator, since this is a 4" fall on aiders from a placement with no rope attached. I figured 4" is about the height of my bounce testing.

This gave me a fall factor of two, which I think is appropriate. The calculator gave an anchor impact of 18.37kN, which I believe is around 4,126 pounds. So, a successful bounce test would mean that the placement held to around 4,000 pounds. Since a dynamic rope would then be attached to the placement, it seems that the placement would probably hold a fall, given the lower fall factor and rope stretch.

I've never had physics so I don't know if this is correct, but it would justify the climber's remark.

Do you know if this is correct?


coomer


Jul 9, 2004, 9:22 PM
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I heard an aid climber say that if you agressively bounce test your placements you can be fairly confident that earlier placements will hold if the current one fails. I am new to aid climbing so I don't have any experience with which to judge his remark.

I found his remark hard to believe, but after doing some research I can now see his point.

Using the impact force calculator at www.myoan.net/climbart/climbforcecal.html, I entered a weight of 180#, a rope length of .16667 feet (two inches) and a distance also of .16667 feet. I clicked the static rope indicator, since this is a 4" fall on aiders from a placement with no rope attached. I figured 4" is about the height of my bounce testing.

This gave me a fall factor of two, which I think is appropriate. The calculator gave an anchor impact of 18.37kN, which I believe is around 4,126 pounds. So, a successful bounce test would mean that the placement held to around 4,000 pounds. Since a dynamic rope would then be attached to the placement, it seems that the placement would probably hold a fall, given the lower fall factor and rope stretch.

I've never had physics so I don't know if this is correct, but it would justify the climber's remark.

Do you know if this is correct?

Uh... you're kind of off base (big time) with how much force you're putting on a piece by bounce testing. The idea is NOT to put anywhere near 18KN of force on the piece- hell, if you did most moderately hard aid pieces would surely rip.

A bounce test is performed standing in a set of aiders clipped to a high piece- or just hanging off the piece with a daisy. You ease onto it at first (body weight) then give a small bounce with your body (a bit over body weight) and then bounce a little more (twice body weight perhaps) and depending on the piece bounce enough so that the rack is up around your ears- but you're not climbing above the piece and hurling yourself off onto your daisy clipped into the piece (factor 2 fall)- that's a good recipe for death or serious injury. Basically, you want to put about 2-3 times your body weight on the piece (this comes with practice and judgement). After that- you know the piece can hold enough force for a small fall on a dynamic catch (rope, belayer, screamer) as opposed to being able to just hold body weight (hanging on the piece).

Fuck this is long winded for a pretty basic concept.

Get on the piece, and bounce up and down while standing in an aider on the piece. The harder you bounce- the more force- the better the piece (if it doesn't rip)

The only way to stay moderately safe on desperate aid is to bounce test every piece. The only time I don't bounce is if it's an obvious bomber piece- fat came in an A1 crack that will hold a truck- or on really, REALLY fragile features- detatched flake that I'm hooking. Everything else gets a bounce. If I'm scared shit-less- I'll bounce a little harder. If it's a pretty decent piece- a quick bounce just to make sure it's set is enough for me.

Cheers
doc


Partner rgold


Jul 9, 2004, 9:41 PM
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I think it is way off.

If you are taking a 4 inch bounce on a step that is, say, five feet from the piece you are testing, then the fall factor is 4/60=1/15. Petzl has found webbing slings have a UIAA impact rating in the 20 kN range. Using this figure, a four-inch bounce would generate about 4.6 kN (1000 lbf). If you are using a rope with a UIAA rating of 8.5 kN and if (this is a very big if on an aid pitch) the friction through the lower biners is negligible, then your 4.6 kN piece should be able to handle a .13 fall factor fall. (Of course, you don't know what it can actually handle, all you know is that it could have handled at least .13 fall factor fall before you bounced on it.) Some but not all aid falls would meet this criterion---you'd have to be at least 20 m up the pitch or more to have fall factors that low if you fall with your waist four feet above the tested piece.

In reality, friction through the lower biners may reduce the amount of rope available for stretching and generate loads that would normally be associated with higher fall factors. This doesn't change the bounce test estimate, but it means that in real life a .13 fall factor fall may blow a bounce-tested piece.

I'd say the short answer is that the bounce test does not guarantee the piece will catch you if the next piece blows. Your chances to be caught improve the shorter your actual fall and the farther away from the belay you are. If the rope zig-zags through the lower biners, all bets are off.


jimdavis


Jul 9, 2004, 9:41 PM
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The idea is to be confident that your pieces will hold below you, yes.

Your basically building links in a chain with each piece you place, if you don't bounce one, and don't have confidence in it...then you won't feel comfortable really bouncing on the next piece, and it continues until you: 1)sh*t yourself.
2) you find a BOMBER placement you know you can trust and you start building a new "chain".
3) you stop sucking your thumb and make it to the top, and shortly there-after sell you aid rack.

SO...go nuts on those bounce tests, and really feel comfortable climbing above them. The more you do it, the more comfortable you'll feel, and the faster you'll get.

As to falling, try not to do it on your daisies...bad stuff can happen.

Cheers, and happy aiding.
Jim


Partner coylec


Jul 9, 2004, 10:54 PM
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Having read a bunch of stuff regarding bounce testing versus funk testing, I talked to Pete about this last month. He said that a while back, someone had written into that Dr. Piton column asking about both methods. R&I's editor, Duane Raleigh, has a dynometer and did some field work for Pete. Duane was able to get 500 to 1100 lbs of force by aggressively bounce testing (~220lbs = 1kN, making that 2.2kN to 5kN). Using a funkness device (swaged metal cable usu. used for piton removal by attaching one end to the piton and the other to your hammer), he was able to generate over 2000 lbs of force (9kN). For this reason, you're going to want to bounce test instead of funking: with bounce testing, you get a better feel for how much force you are generating than with your hammer.

This means that your numbers are off by a factor of 4 ... big wall theory vs. big wall fact :wink: . If you don't believe me, check out his reply from Rock and Ice. There's a link at the bottom which lets submit questions ... and if you're question gets picked, you get free swag.

jimdavis is on the mark: you want to be building a string of exclamation points, not question marks. And if you don't think daisy falls are bad, ask Pete :D .

coylec


coomer


Jul 9, 2004, 11:00 PM
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Having read a bunch of stuff regarding bounce testing versus funk testing,
coylec

I do a mix of both... when I first started aiding, I did a lot of funk testing being too chicken shit to get on a bounce test. But now, I only funk if the placement is difficult to get on to bounce test- mostly roof moves, or sideways hooking- I'll funk- but not too hard- just to make sure the piece is set enough to get on, then I'll bounce test. I'll agree that you get more of a feeling from bounce testing than funk-ness testing. It's still nice to funk a piece that's dicey to even get onto. Blind placements are another good option for a small funk-test before stepping onto it. That way, you can be fairly certain it won't pop before you can even stand on it.

Cheers
doc


Partner coylec


Jul 9, 2004, 11:07 PM
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True dat -- I'll funk crappy hooks in a heart beat -- when you fail a bounce on that, you're asking to take a ride. I wasn't trying to suggest that funking was always bad -- rather i'd bounce 99% of the time and only funk in rare occaissions.


alpnclmbr1


Jul 9, 2004, 11:17 PM
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The cables on stoppers break at 3 to 10kn
Cams range from 7kn to 15kn
At 18kn you would be lose to breaking bomber 3/8" bolts.

The falling climber breaks at 12+kn

Read rgolds post again.


jcain


Jul 10, 2004, 7:18 AM
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Thank you all for the clarification! I really appreciate it.


brutusofwyde


Jul 19, 2004, 4:29 PM
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True dat -- I'll funk crappy hooks in a heart beat -- when you fail a bounce on that, you're asking to take a ride. I wasn't trying to suggest that funking was always bad -- rather i'd bounce 99% of the time and only funk in rare occaissions.

Easy easy aid, no testing needed.

moderate aid, I bounce test.

hard-to-bounce pieces, I funk.

Once-in-a-lifetime string of dicey if-you-fall-you-die placements, these days I funk with a 1/16" circle of swaged cable until the cable breaks or pulls out of the swage. (Thanks, FISH!)

Good to see you posting more, Eric!

Brutus


Partner coylec


Jul 19, 2004, 5:10 PM
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Once-in-a-lifetime string of dicey if-you-fall-you-die placements, these days I funk with a 1/16" circle of swaged cable until the cable breaks or pulls out of the swage. (Thanks, FISH!)

Are these the new gizmos that Russ mentioned on the site like 6 monthes ago? I don't see 'em on the website, though :cry:

What's the breaking strength on the swage?
Could you PM me details and a link? please, oh please, oh please!

coylec


areyoumydude


Jul 19, 2004, 5:55 PM
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True dat -- I'll funk crappy hooks in a heart beat -- when you fail a bounce on that, you're asking to take a ride.
I never bounce test hooks. I do get on them while I am tethered short to my last piece. I will then sway around on the hook simulating the angles of movement that I will be putting on it once I feel confident to move up on it. If it does pop I won't be taking a ride. I will just be hanging on my last piece.


Partner coylec


Jul 19, 2004, 8:14 PM
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In reply to:
True dat -- I'll funk crappy hooks in a heart beat -- when you fail a bounce on that, you're asking to take a ride.
I never bounce test hooks. I do get on them while I am tethered short to my last piece. I will then sway around on the hook simulating the angles of movement that I will be putting on it once I feel confident to move up on it. If it does pop I won't be taking a ride. I will just be hanging on my last piece.

Still doesn't test the strength of the rock you're on. Hooks put a lot of pressure on the rock ... You get full weight on it when you cinch up your daisy and stand up on the piece ... if it blows, you're taking a ride ... or worse, a static daisy fall. If it's in line and I can bounce it without risking a ride, i'll bounce ... otherwise, I do a light funk. Experience has shown me that testing hooks is important.

coylec


climbtothebeet


Jul 19, 2004, 8:25 PM
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sombody say either "yes bounce testing works" or "no, u stupid macaroni face, u will die"
thankyou


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