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Quick Study Involving Falls on Static Materials
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USnavy


Jul 28, 2013, 8:43 PM
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Quick Study Involving Falls on Static Materials
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While bored over the last few days, I decided to create a quick, nonchalant study contrasting static falls with various slings. The testing parameters were simple: I took 10 – 11 falls on four different slings; a Metolius PAS, a 1” nylon sling, a polyethylene sling and a piece of dynamic rope; and I then repeated the test with a rigid mass, dropped at a greater height. However, the primary function of this study is in relation to the first test and first two graphs showing the relationship between different sling types.



Test one:
- 160 lb flexible mass
- Fall factor 0.22
- Fall distance, 5 – 5.5”, adjusted to ensure appropriate fall factor

Test two:
- 11.5 lb rigid mass
- Fall factor 1.05
- Fall distance 24 – 26”

First, a quick rundown of the testing methods. In the photo below, you will notice three pieces of material: a 9.1mm yellow rope, a green rope (the test sample) and a piece of green webbing with tape on it. In order to execute the test I would use the GriGri, with my weight held by the yellow rope, to position properly myself as indicated by the tape on the green sling. Then, when ready, I would activate a quick release, which would drop me directly onto the sample, 5 – 5.5”. Last, I would stand back up and repeat the test another nine times.



After running through four testing samples, I repeated the test with a solid-steel hoop, which I referenced above as “test two.” In test two, I did not use a quick release, but rater I picked the hoop up and carefully dropped it directly in line with the load cell.












(This post was edited by USnavy on Jul 29, 2013, 5:20 PM)


Syd


Jul 29, 2013, 4:29 AM
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Re: [USnavy] Quick Analysis: Flexible Masses vs Rigid Masses on High-Impact Falls [In reply to]
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USnavy wrote:
... Part of the reason why the standard deviation is so high with the ridged-mass trials, relative to the flexible-mass trials, is because of the lack of a load-absorbing component of a flexible human. Of course, the other reason why the standard deviation is rather high is because this was an informal test and therefore slight deviations in the exact placement of the hoop before I dropped it adversely affected the readings, as well as technicalities involving the mass of the load cell.

Interesting but a pity you didn't do a 1:1 comparison.

I'd expect using a human rather than a rigid body should give a greater variation. The fact that it didn't indicates your latter explanation "deviations in the exact placement of the hoop ".


Kinobi


Jul 29, 2013, 5:48 AM
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Re: [Syd] Quick Analysis: Flexible Masses vs Rigid Masses on High-Impact Falls [In reply to]
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A lot of testes with "real" human body, and with metal mass were done by CAI (Italian Alpine Club). There was no significant difference in results.
Best,
E


Syd


Jul 29, 2013, 2:12 PM
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Re: [Kinobi] Quick Analysis: Flexible Masses vs Rigid Masses on High-Impact Falls [In reply to]
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Kinobi wrote:
A lot of testes with "real" human body, and with metal mass were done by CAI (Italian Alpine Club). There was no significant difference in results.
Best,
E

Link please ? Hopefully in English ...


distantThunder


Jul 29, 2013, 6:54 PM
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Re: [USnavy] Quick Study Involving Falls on Static Materials [In reply to]
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good job. don't stop there! keep up the good work.
nothing beats real data.

dT


Kinobi


Jul 29, 2013, 9:18 PM
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Re: [Syd] Quick Analysis: Flexible Masses vs Rigid Masses on High-Impact Falls [In reply to]
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Google translater does miracles.
E


Syd


Jul 29, 2013, 9:53 PM
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Re: [Kinobi] Quick Analysis: Flexible Masses vs Rigid Masses on High-Impact Falls [In reply to]
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Kinobi wrote:
Google translater does miracles.
E

It does need something to translate though ;-)

I did find this which is interesting: http://www.beal-pro.com/anglais/facteurchute.php


distantThunder


Jul 30, 2013, 6:27 AM
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Re: [USnavy] Quick Study Involving Falls on Static Materials [In reply to]
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USnavy
by the way - to make your drop tests more "systematic" ... how about if you vary the test conditions so that the total potential energy in the fall is the same? in other words, keep mass x gravity x (drop height) the same for each set of tests. therefore, if you reduce the weight of the falling object by a factor of 10, increase the distance it falls by the same factor.

there is no rule that says that "energy" should be the one critical factor that you use for scaling your tests. but it's a convenient place to start.

cheers,
dT


(This post was edited by distantThunder on Jul 30, 2013, 6:28 AM)


MFC


Jul 30, 2013, 10:22 AM
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Re: [distantThunder] Quick Study Involving Falls on Static Materials [In reply to]
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For those interested is seeing some test results for steel weights vs. humans vs. test dummies there was a paper presented in 2009 at the International Tech Rescue Symposium (ITRS) -

"On the Utility of Rescue Randy Mannequins in Rescue System Drop Testing"

www.itrsonline.org/papersfolder/2009/Holden-May-Farnhamn2009_itrspaper.pdf


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