Looking for some numbers for various webbing anchor configurations. We know end to end it's 4000 lbs. Some sources say a wrap 3 pull 2 is rated at 16000, some say 8000, & some say 5000. Had a pretty long discussion in a class this weekend and the bottom line ends up being that you can get whatever number you want depending on what you read. Does anyone know of any studies or info that substantiate the true MBS of the configurations?
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Thread: 1" tubular webbing strength
03-23-2011, 04:09 PM #1
1" tubular webbing strengthJohn D. Calamia, BS, NREMTP, FP-C
03-23-2011, 09:15 PM #2
I have a whole book on nothing but testing of rope equipment. Hell they even whent as far as snipping a little bit at a time away at webbing until it broke while under load. It had got further then half way through before it broke! I will dig it up for you tomorrow and post for ya. The testing comes from the company All About Ropes. can be seen at same web site name. great people over there.
03-25-2011, 07:35 PM #3
03-27-2011, 11:11 AM #4
http://www.caves.org/commission/ncrc/national/ cannot find the study info, but contact them and sure someone can help.
1" tubular webbing is usually rated at 18k/N (~4000 lbf). Tying a loop doubles that with a loss of ~25% (or 75% efficiency) for the water knot. Note that the loss of strength is only on the section with the knot. So... a simple singular loop around an anchor would give about 7000 lbf [4000 + (4000 * .75)]. A doubled loop would give about 15,000 lbf [4000 + 4000 + 4000 + (4000 * .75)].
Since a wrap three, pull two tied correctly has the water knot in the non-loaded wrap, it takes the 75% efficiency out of the mix and the 2 loaded wraps are each at 100%. In theory this would give all 16,000 lbf available to the anchor.
None of these figures take out the loss for a sharp bend where the webbing wraps into the carabiner, but...
May I ask what the debate was at your station?
Last edited by FiremanLyman; 03-27-2011 at 11:13 AM.~Drew
USAR TF Rescue Specialist
03-27-2011, 03:33 PM #5
The discussion just stemmed around the true breaking strengths of the webbing and how multiple resources have multiple values. We were just looking to substantiate the actual numbers.John D. Calamia, BS, NREMTP, FP-C
12-22-2012, 02:21 AM #6
I hate to revive on old thread, but I must as I too have been finding conflicting information on web anchor MBS. I too have heard that with a basket and W3P2 that you have about 4000 lbf per strand giving 16,000 lbf.
But from CMC's own rescue manual I found these images:
And then there is this study which agrees more with CMC numbers:
This image from the study
I get the concept behind 4000 lbf per strand, but maybe this just works on paper?
12-22-2012, 10:27 AM #7
- Join Date
- Jul 2006
- Southern Illinois
From http://www.firehouse.com/forums/t125756/ (Anchor Webbing)
Drawn on paper, the w3p2 appears that it should be 16,000# in strength. But slow pull tests often average in the 35-40KN range, as the inner section of webbing is pinched between the outer section and the carabiner, creating fusion and then failure.
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