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Home > miscellaneous junk/projects > load testing
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the drop-test rigging, about forty five feet up in a tree. the primary drop anchor is the orange steel lifting ring (oval) on the top right. it is hanging under a ~11" diameter horizontal tree branch, by double-wrapped 2" nylon seatbelt webbing to keep the system as static as possible (so as to generated higher forces). this is also backed up with a loose loop of climbing rope (brown, double fish knot) in case the massive static load broke the webbing (i didnt know what to expect, and the webbing was used).

the sample is between shackles under this, but is hard to make out because you are looking directly through it. you can see that it is not just a loop with one seam- it actually has a seam on each side so i could effectively test two seams simultaneously.

if the sample breaks, two cascaded backups will engage to slow the weight down so that it doesnt hit the ground and destroy something. the first is the unweighted green rope, which is a ~9.2 dynamic with several turns through a friction shock absorber (camp or kong device). the second is a fatter section of dynamic rope threaded a couple times through a second absorber. the end result is that theoretically (no sample broke during testing) the sample sling will break, will free fall a couple more inches, the green rope will pull tight and start burning through the absorber (slowing it down slowly) and after another meter the secondary absorber will kick in in parallel and slow it down significantly more. (the meter of slack looks like less because it is in a loop in plane with the photo as taken).

i cant remember what the drop distance was, but theoretically it shoudlnt matter. it was as close to a factor-2 fall as i could engineer, which is what determines the force. it was probably about a 16-18 foot free fall. the rope was a fat heavily used and retired dynamic rope, around 10.5 but its hard to know given how old it is. suffice to say it was probably halfway to being a static rope, and it was re-used for subsequent drops which meant any give in the knots while they were set under load, and the reduced give in the primary rope after a high load, would result in even higher forces on subsequent drops. and further still- there was no give in the belay (top anchor) or the load (solid concrete tied directly to rope) which also results in higher-than-real-world fall forces.

the biners involved were taped so that in the dynamic drop event nothing would get cross-loaded. the orange flagging is to identify biners used for the drop testing which i am no longer considering safe for climbing.

keywords: testjig, droptest

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