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redlude97
Aug 11, 2010, 7:02 PM
Post #126 of 140
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Rudmin wrote: cracklover wrote: rgold wrote: [img]http://usera.ImageCave.com/rgold/Technical/Anchor.png[/img] This is, as claimed earlier, a version of the so-called American Death Triangle, a configuration that, while not ideal, isn't nearly as bad as its name suggests in many situations. This being one of them. This anchor is nothing to freak out over if the bolts are reasonable. But still, it isn't ideal; for the situation pictured, in-line clove hitches would have made much more sense. My physics is extremely rudimentary, so forgive me if I'm missing something obvious. But one implication of your equation above is that any time the two angles are equal, the force on the anchor is exactly L. Intuitively, this seems a little odd, since one could imagine a standard ADT anchor in which those two angles were equal (an equilateral triangle would do it) and in which we know that both bolts definitely see a force > L. GO That is why it's bad. We have two bolts that both get the full load on the anchor. If you build a two piece anchor properly, each bolt should get half of the load. 
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redlude97
Aug 11, 2010, 7:08 PM
Post #127 of 140
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jt512 wrote: redlude97 wrote: When discussing the forces on the pulley itself the forces are magnified relative to the input force. I still think that is a silly way to think about the problem. Whatever weights you apply to either a fixed pulley or a bolt, the force on the pulley or bolt is still just a function of those weights. And if I interpret Rudmin's linked video correctly, then the force in the pulley case never be more than the force in the bolt case, and it will be less when the weights are unequal. So it seems to me that a single fixed pulley, if anything, is a force diminisher. Jay
This is all pertinent to the ADT because the force on each anchor point is higher than what it would be for a V setup for the exact same input force(load). This is due to the ADT utilizing a pulley setup.
Edited to add: To clarify, in a pulley 1 of the load strands is fixed so it should not be considered an input force.
(This post was edited by redlude97 on Aug 11, 2010, 7:10 PM)
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cracklover
Aug 11, 2010, 7:08 PM
Post #128 of 140
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Rudmin wrote: cracklover wrote: rgold wrote: [img]http://usera.ImageCave.com/rgold/Technical/Anchor.png[/img] This is, as claimed earlier, a version of the so-called American Death Triangle, a configuration that, while not ideal, isn't nearly as bad as its name suggests in many situations. This being one of them. This anchor is nothing to freak out over if the bolts are reasonable. But still, it isn't ideal; for the situation pictured, in-line clove hitches would have made much more sense. My physics is extremely rudimentary, so forgive me if I'm missing something obvious. But one implication of your equation above is that any time the two angles are equal, the force on the anchor is exactly L. Intuitively, this seems a little odd, since one could imagine a standard ADT anchor in which those two angles were equal (an equilateral triangle would do it) and in which we know that both bolts definitely see a force > L. GO That is why it's bad. We have two bolts that both get the full load on the anchor. If you build a two piece anchor properly, each bolt should get half of the load.
Okay, sounds like I'm not missing anything. Thanks for the second set of eyes.
GO
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hafilax
Aug 11, 2010, 8:20 PM
Post #129 of 140
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cracklover wrote: Rudmin wrote: cracklover wrote: rgold wrote: [img]http://usera.ImageCave.com/rgold/Technical/Anchor.png[/img] This is, as claimed earlier, a version of the so-called American Death Triangle, a configuration that, while not ideal, isn't nearly as bad as its name suggests in many situations. This being one of them. This anchor is nothing to freak out over if the bolts are reasonable. But still, it isn't ideal; for the situation pictured, in-line clove hitches would have made much more sense. My physics is extremely rudimentary, so forgive me if I'm missing something obvious. But one implication of your equation above is that any time the two angles are equal, the force on the anchor is exactly L. Intuitively, this seems a little odd, since one could imagine a standard ADT anchor in which those two angles were equal (an equilateral triangle would do it) and in which we know that both bolts definitely see a force > L. GO That is why it's bad. We have two bolts that both get the full load on the anchor. If you build a two piece anchor properly, each bolt should get half of the load. Okay, sounds like I'm not missing anything. Thanks for the second set of eyes. GO
I'm sure the gallery will correct me if I'm wrong.
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milesenoell
Aug 12, 2010, 8:42 PM
Post #130 of 140
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Does anyone here ever actually use an ADT? If so, when?
I expect that some old-timers have used them, but I'm I have doubts that even those who used to use them are using them any longer. Entirely possible that I just haven't gotten out enough and don't know what folks are using, so I thought I'd ask.
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kjaking
Aug 12, 2010, 9:36 PM
Post #131 of 140
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hafilax wrote: The dangerous issues with the ADT, AFAIK, were twofold: the sling was often run through the hangers without biners making for a cutting hazard and when used to rappel the rope was often run directly off the sling which can severely weaken the sling once the rope is pulled. These practices were done in order to minimize gear left behind when rappelling but make for a dangerous anchor for the next party that comes across the setup. I'm sure the gallery will correct me if I'm wrong. |
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cracklover
Aug 13, 2010, 4:11 PM
Post #132 of 140
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milesenoell wrote: Does anyone here ever actually use an ADT? If so, when? I expect that some old-timers have used them, but I'm I have doubts that even those who used to use them are using them any longer. Entirely possible that I just haven't gotten out enough and don't know what folks are using, so I thought I'd ask.
Yes. Often when rappelling on routes in which the anchors are two side-by-side bolts, I will clip in via a sling girth-hitched to my harness, with a biner clipped to each hanger. This creates an ADT. I'm fine with that.
GO
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jjones16
May 22, 2011, 6:55 AM
Post #133 of 140
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This confuses me. If I ever did something like this, I sure as hell wouldn't post it.
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dugl33
May 22, 2011, 2:36 PM
Post #134 of 140
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jjones16 wrote: This confuses me. If I ever did something like this, I sure as hell wouldn't post it.
I didn't do it -- I came across the pic researching routes and thought it was an odd set-up, that's all.
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jgibson2721
Jun 26, 2011, 12:15 AM
Post #135 of 140
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I would have at bare minimum utilized a cordellete for a warm and fuzzy.
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scrapedape
Jun 26, 2011, 11:35 AM
Post #136 of 140
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jgibson2721 wrote: I would have at bare minimum utilized a cordellete for a warm and fuzzy.
Oy. If there's one thing that's come out of this thread, it's that there's plenty that could be done to make this anchor better with the materials in the photo. A cordellete definitely is not part of the bare minimum to make this anchor adequate.
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healyje
Jun 26, 2011, 11:47 AM
Post #137 of 140
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billcoe_ wrote: He could have just as easily clipped the chain, cloved that biner, and ran the rope up to the next bolt and cloved that biner.
Not sure this thread needed a lot more discussion past this...
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sp115
Jun 27, 2011, 1:25 PM
Post #138 of 140
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healyje wrote: billcoe_ wrote: He could have just as easily clipped the chain, cloved that biner, and ran the rope up to the next bolt and cloved that biner. Not sure this thread needed a lot more discussion past this...
+1, and yet every time I run across a thread like this I feel compelled to read and it...
(This post was edited by sp115 on Jun 27, 2011, 1:25 PM)
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Sforscott
Aug 6, 2011, 5:15 AM
Post #139 of 140
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Registered: Jul 4, 2011
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edge wrote: Umm, yeah. I would have handled that scenario differently.
Looks like an ugly z clip
(This post was edited by Sforscott on Aug 6, 2011, 5:16 AM)
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jt512
Aug 6, 2011, 5:40 AM
Post #140 of 140
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Sforscott wrote: edge wrote: Umm, yeah. I would have handled that scenario differently. +1 Looks like an ugly z clip
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