At the International Tech Rescue Symposium in 2004,
three authors from CMC Rescue presented some rope strength tests
where a bight of rope was run around round rods of different diameters.
The rope was 11 mm kernmantle, but the material was not specified.
CMC makes both nylon and polyester ropes.
www.itrsonline.org/PapersFolder/2004/SmithCedric-McKently-Parker2004_ITRSPaper.pdf
Thanks much for this.
Re material, possibly one can check current CMC ropes data
and get a good idea of the rope, but it's a pretty sad state of
presenting test results that something as fundamental as test
specimen make-up isn't reported! --this is especially annoying
in the tests of chemicals on rope (DEET & spit chewing tobacco).
Maybe one should presume there that it was a combination
nylon-polyester (PA/PS(PES)) rope? Acids more likely hurt
PA, alkalis PES --something like this.
It's interesting to see the pulled-bight data:
the "control" data came in pulling a single strand end-2-end
with ends wrapped around 4" bollards; so, one should expect
at most twice this strength for a (2-strands) bight.
But there are higher test results for pulling a bight
starting at the 1.5" bight-pin !
.:. Perhaps there is a
fatigue factor at play?!
For
What is different? in the loading of rope around
opppsed bollards (with multi-wraps) and the test specimens
having this for the legs, yes, but in opposition to a bight
around pins (of various sizes)? --the difference is the bight,
which has but a turn, no wraps!
And this does what? This reduces the amount of material
feed into the tension zone, and so reaches higher tensions
per time (there being less incremental stretch out of the bight),
whereas the wraps delay these tensions a little.
Perhaps in more rapid loading, the bight would show some
disadvantage?
It's also interesting to consider the case of the large-diameter
bight,
given how CMC's test device oriented the bight
--i.e., pin cylinder is parallel to bollard, AND bight legs go
to SAME SIDE of bollard. Exaggerate the pin size to see what
the effect is : the bight leg going from top-side (both legs do)
DOWN to bottom of the pin is well longer than the other leg.
(CMC sh/could've wrapped the bollard differently, legs going
to opposite sides (and either making an X crossing or not!).)
As for the fire-situation exposure, it's not clear to me exactly
what was done, here : e.g., were the ropes merely coiled and
attached to the firefighter and so brought into the stated conditions,
but still (1) in a coil & (2) not tensioned or used in any way?
That I'd think would suggest that rope more exposed, lying
outside of the coils, would suffer more. Maybe the test specimens
ensured that some such part of the rope was tested.
Finally, re the chewing-tobacco testing, the last specimen is cited
as having "slipped" : huh, what does this mean? --slipped in the
clamped-onto-bollard attachment?!
--dl*
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