|
scottek67
Jan 19, 2010, 11:40 PM
Post #2 of 45
(25300 views)
Shortcut
Registered: Apr 6, 2008
Posts: 515
|
|
|
|
|
|
Rudmin
Jan 19, 2010, 11:48 PM
Post #3 of 45
(25296 views)
Shortcut
Registered: Mar 29, 2009
Posts: 606
|
I am guessing that this isn't what it appears to be. Haven't bothered to check the file.
EDIT: I stand corrected
(This post was edited by Rudmin on Jan 19, 2010, 11:53 PM)
|
|
|
|
|
Rudmin
Jan 20, 2010, 12:13 AM
Post #4 of 45
(25266 views)
Shortcut
Registered: Mar 29, 2009
Posts: 606
|
Interesting stuff. The way the anchor failure tests happened with the weight hanging and an anchor suddenly releasing seems a bit cut and dry. I wonder if there would be any difference in the anchor failure tests if you had a falling mass (climber) pull out the anchor via some sort of preplanned weak point so that you get the full dynamic effect of the momentum of the climber and the shock vibrations in the rope..
|
|
|
|
|
rightarmbad
Jan 20, 2010, 12:53 AM
Post #5 of 45
(25246 views)
Shortcut
Registered: Mar 22, 2005
Posts: 218
|
They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems.
The ideal could never be what they postulated.
|
|
|
|
|
adatesman
Jan 20, 2010, 1:05 AM
Post #6 of 45
(25238 views)
Shortcut
Registered: Jul 13, 2005
Posts: 3479
|
|
|
|
|
|
patto
Jan 20, 2010, 8:21 AM
Post #7 of 45
(25164 views)
Shortcut
Registered: Nov 15, 2005
Posts: 1453
|
All the extension results from this testing are absolutely bogus for most climbing and rescue situations. They are getting 18kN+ loads because there is nothing dynamic in the system.
A mass should NEVER be directly attached to an anchor that can extend. Either ensure that there a dynamic attachment or that the anchor has absolutely minimal extension.
Thats I cannot fault the equalisation testing. Given the nature of this debate everybody will take their own personal slant on this study.
Personally after looking at the load sharing ability of the equalette vs the cordalette I fail to see a good reason why I should use an equalette. I've said it before K.I.S.S.
(This post was edited by patto on Jan 20, 2010, 8:22 AM)
|
|
|
|
|
scottek67
Jan 20, 2010, 9:17 AM
Post #8 of 45
(25154 views)
Shortcut
Registered: Apr 6, 2008
Posts: 515
|
adatesman wrote: For anyone who'd rather not register to a suspicious file sharing service I've put a copy of the PDF here. 
(This post was edited by scottek67 on Jan 20, 2010, 1:05 PM)
|
|
|
|
|
cracklover
Mar 23, 2010, 4:50 PM
Post #9 of 45
(24687 views)
Shortcut
Registered: Nov 14, 2002
Posts: 10162
|
This is excellent! I hadn't seen it before! Some of the results are predictable, but it's good to see real data!
The loads here seem reasonable for a rescue situation, but, unfortunately, not for most pure rock climbing situations.
Still, it does at least *hint* at the truth of what might happen in a hanging belay off an anchor when one arm blows. And if the loads were those you'd see in a worst-case scenario (which is exactly the one you build your anchor to handle) then you might expect to see loads like those in the study.
The main thing I wish is that they'd included some of the better anchors from the big anchors thread. Things like the CharlesJMM and the Mooselette make the equalette look like a poor first draft (IMO).
The best of the bunch in the thread were a beautiful blend of what the study calls load-sharing and load-distributing, with features of each. Unlike the load-sharing anchors in the study, these anchors had very little extension. The only real question is how well they'd equalize in a drop scenario - an answer that would have been well tested by this study.
GO
|
|
|
|
|
bigjonnyc
Mar 23, 2010, 6:21 PM
Post #11 of 45
(24602 views)
Shortcut
Registered: Dec 17, 2004
Posts: 369
|
cracklover wrote: rightarmbad wrote: They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated. I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this: [image]http://i43.tinypic.com/qoc1o5.jpg[/image] What are you seeing that I'm missing? GO
Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.
|
|
|
|
|
cracklover
Mar 23, 2010, 6:35 PM
Post #12 of 45
(24589 views)
Shortcut
Registered: Nov 14, 2002
Posts: 10162
|
bigjonnyc wrote: cracklover wrote: rightarmbad wrote: They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated. I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this:  What are you seeing that I'm missing? GO Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting.
That's not necessarily an problem - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points.
But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal.
This is now what the forces look like they should be. So they look to me like (friction etc aside) they should be equal on each strand.
Edited to add pic ^^^
GO
(This post was edited by cracklover on Mar 23, 2010, 7:16 PM)
|
|
|
|
|
bigjonnyc
Mar 23, 2010, 7:05 PM
Post #13 of 45
(24564 views)
Shortcut
Registered: Dec 17, 2004
Posts: 369
|
cracklover wrote: bigjonnyc wrote: cracklover wrote: rightarmbad wrote: They stuffed up with the twin sliding X, of course the centre anchor is going to see twice the load, it's connected to both systems. The ideal could never be what they postulated. I'm not at all clear on why this should be. A simple diagram (ignoring for the moment the force multiplication through angles, and any friction/binding) suggests that the forces should look like this: [image]http://i43.tinypic.com/qoc1o5.jpg[/image] What are you seeing that I'm missing? GO Somehow your diagram is messed up. With a pull of X>0 on the bottom, this system will not remain static. Both the center and right anchors in your diagrams have uneven pulls from opposite sides of the webbing running through them. In a physical context this means acceleration, or one side of the anchor extending and the other contracting. That's not necessarily an issue - a standard cordelette will have differing tension in every arm. It simply means that there is uneven stress on the anchor points. But upon further reflection, there *is* an issue with my diagram above: assuming no friction, the tension in every strand should be equal. Will post another version shortly. GO
That's what I meant by uneven pulls, differing tension on opposite sides of the cordolette running to an anchor
|
|
|
|
|
rightarmbad
Mar 29, 2010, 10:14 AM
Post #14 of 45
(24440 views)
Shortcut
Registered: Mar 22, 2005
Posts: 218
|
The way I read it was that they had a sliding x between anchor 1 and 2, a sliding x between anchor 2 and 3, then a sliding x to join the 2 original x's.
This would mean that anchor 2 was repesented in both x's and therefore would see twice the load and that would agree with their results.
|
|
|
|
|
ptlong
Mar 29, 2010, 10:08 PM
Post #18 of 45
(24222 views)
Shortcut
Registered: Oct 4, 2007
Posts: 418
|
GO, are you sure you can really see that poor photograph well enough to draw an accurate diagram? It sure isn't clear to me. While your sketch might be correct I think it's just as easy to see it as two sliding Xs with four strands going to the center anchor.
Now that would require you to believe that they screwed up their calculation of the ideal static loads. But look at the equalette case. They screwed up the ideal values for that one.
|
|
|
|
|
ptlong
Mar 30, 2010, 12:27 AM
Post #20 of 45
(24161 views)
Shortcut
Registered: Oct 4, 2007
Posts: 418
|
I don't see 4 strands. But I don't see the one crossing from left to right down below either.
Here's another bad photo. It's not so bad that you won't be able to tell the configuration but I think it makes my point.
 
|
|
|
|
|
davidnn5
Mar 30, 2010, 7:25 AM
Post #22 of 45
(24091 views)
Shortcut
Registered: Dec 8, 2009
Posts: 348
|
Without wanting to sound too unscientific, what are the conclusions of the more gear-headed people here? I hate using webbing to start with as anchors and will generally use lengths of static rope with appropriate knots etc. I have money, and will pay for my life to be secure up to ~30kn. And wear a helmet. Yes, I'm that uncool.
(This post was edited by davidnn5 on Mar 30, 2010, 7:27 AM)
|
|
|
|
|
rightarmbad
Mar 30, 2010, 10:01 AM
Post #23 of 45
(24070 views)
Shortcut
Registered: Mar 22, 2005
Posts: 218
|
The original link I followed never showed any piccies.
I shall have another look.
|
|
|
|
|
ptlong
Mar 31, 2010, 2:54 AM
Post #24 of 45
(24001 views)
Shortcut
Registered: Oct 4, 2007
Posts: 418
|
GO, I see what you're talking about and it is suggestive. But I don't think this photo is good enough to really say one way or the other. It's just too easy to see things in a lousy photo, especially if you're already thinking it's supposed to be there.
Let's take another tack. If you're interpretation is correct the force on each anchor should be the same ideally. The angle between the left and right anchors looks like about 85 degrees or so. For the 595 lb load that would give a value of 240 lbs on each anchor.
If instead four strands go to the center, the ideal would be 171 lbs for the side anchors and 342 lbs for the center one.
The actual mean values they measured were: 195 lbs (left) 365 lbs (center) 189 lbs (right).
Now any monkey would quickly discover that this anchor binds like crazy. But is this the reason the results do not come close to matching the ideal case? Or is it rigged so that it wouldn't?
I don't know.
(This post was edited by ptlong on Mar 31, 2010, 2:56 AM)
|
|
|
|
|
cracklover
Mar 31, 2010, 3:57 PM
Post #25 of 45
(23088 views)
Shortcut
Registered: Nov 14, 2002
Posts: 10162
|
ptlong, I'm open to other interpretations of the pic, because, as you said, the detail in the pic is poor. But the photo is far from uninterpretable. Sure, it is difficult to tell where the strands are going as they get to the two power-point biners, so I'm open to other interpretations. But beyond that, you can easily see every strand, and there are not four strands going to the middle anchor.
If you want to make an argument about how either the binding or the large angle could result in the data shown in the article, or if you see the configuration of the sling more clearly than I, in a way that's more consistent with the test results, I'm all ears. But just to say that the data from the forces prove configuration "X" does not make "X" so, when the other data (the photo) clearly invalidates "X" as an answer.
I suppose you could also argue that the pic displayed with that set of data was not actually the anchor configuration tested. That would be a serious allegation against the authors of the article, but at least it would be consistent with the data.
GO
|
|
|
|
|
|
|
|
|
1
