Death triangle

[Paul_detrick]

I know this was on here not so long ago, but the last couple times I've been out I've come across them, people please don't use them. On one they used two peices of webbing, so I untied them and put them one from each achor, whats up?

[vraddict]

So what exactly is this death triangle? I have an idea but just want to be clear.

[Figger_Eight]

Ask a gym climber to set up an anchor for you.

[Woody]

AKA the American triangle. You can take a look at it here

 

[ 05-27-2002, 08:30 PM: Message edited by: Woody ]

[JayB]

http://www.climbing.com/Pages/Techtip_pages/195/images/TT-195-trad-fig03.html

[Gimpy]

With out getting to high on a mathematical soap box I'll take a stab at explaining WHY the triangel config. is a poor anchor for those who might be wondering.

 

There are basically two factors at work here. Think of a pulley, by changing the angle or direction of force, you simply put, get more force returned than exerted. The triangle acts as a compound pulley since when force is applied to the anchor you get the force of fall, divided equally to the two outside anchors, with almost no weight bourn by any interior anchors. Now the fun begins when you realize that force traveling through a pivot point, like a pulley or a biner, does not simply cancel it self out but rather redirects. In this case it travels to the other anchor holding the other half of the load. At the same time that anchor is sending it's force the opposite direction and each anchor ends up having to hold not only half the weight of the fall, but the full force being applied to the other side transfered. Add to that the pulley effect and the end result is that each anchor actually has to resist a force greater than the actuall fall generated. You would be better off anchoring to only one point.

 

The second concern is direction of pull, as most anchors are put together to resist a downward pull. The triangle pulls roughly at a 45 degree downward angle. If you want to break metal, the best way is to change the direction of it's stress. Take a paper clip. Bent as it is, for the size it is rather strong. Bend it strait, and back again and you have lost conciderable strength. Do it again and it will likely break. Have one party come along and set up a proper magic X, and the next set up a triangle. Repeat. Repeat again. Slowly the metal get weakened. It is only the excessive strength built into climbing gear that keeps those who don't know better from making grease spots on the ground.

 

Now this is in laymans terms and probably fraught with oppertunities for an engineer to pick it appart but it serves well enough for me.

[Wallstein]

And then there is reality. Two 3/8" bolts slung with an american death triangle isn't that big of a deal when rappelling. Falling on a death triangle is a different story. I wouldn't ever rig some rusty old 1/4" with a triangle but if the bolts were 3/8" and I had only a limited amount of webbing i would be tying "DEATH TRIANGLES".

[Gimpy]

Yes, rappeling is no big deal, since you rarely generate a pull more than your own weight. And top rope climbing is probably no problem since the fall force is only your weight plus the weight of your belayer plus the kinetic energy from whatever distance you fall before being stopped. It's not like people crater all the time from this, especially now that pitons are hardly ever used as anchors anymore. Like I said, it's the excessive strength built into climbing gear that keeps those who don't know better from making grease spots on the ground.

[pope]

If the angle at the bottom of the triangle (call it X) is fairly acute, the two anchors actually share or divide quite a bit of the load. When X=60 degrees (the triangle is regular), each anchor is loaded with whatever load is applied to the "power point". In this case, it is still better to be clipped to the triangle than just one anchor, since there is redundancy and you're clipped to both anchors without applying forces any higher than being clipped to just one.

 

You can model the force applied to each bolt during a 500-pound load at the power point as a function of this angle: F=500sec(X/2)cos((180-X)/4).

 

When X>60, watch out! Applying a load of 500 lbs to the power point might apply even higher loads to each bolt. Even so, the panic over the American Triangle is the result of partial understanding. Turns out that when X=122 degrees, each bolt's load is only double that at the power point....not a great situation, but how often do you see a triangle with an angle that broad at the bottom? I've never seen more than 60 degrees.

 

There is a better system: a long triangle (skinny bottom angle) or two bolts in a vertical line, provided their "weakness cones" don't overlap, rigged such that they share the load.

[spiderman]

come on now. use your head, how good are the bolts? how good is the webbing? How far apart are the bolts?

 

There is no need to be a safety Nazi about two bolts and webbing that are in excelent condition when repelling

[Greg_W]

quote:

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Originally posted by spiderman:

come on now. use your head, how good are the bolts? how good is the webbing? How far apart are the bolts?

 

There is no need to be a safety Nazi about two bolts and webbing that are in excelent condition when repelling

---

Spidey-

You are relying on what you can SEE. What about what you can't see? What about the people who have rappelled in not so smooth fashion? What about cold work on the bolt itself? Since you cannot possibly know the stresses that these bolts have seen in their life, isn't a bit of caution a good idea? Last time I checked, 1" webbing cost about $.25/ft; that's a low price for some peace of mind in my book.

 

Just an extra $.02

 

Greg

[Paul_detrick]

You guys are missing the point, its not the best way, it's easy to have one piece of webbing for one bolt, equalize the anchors, do what you will but I will allways change it.

[aggressivepedestrian]

So does anyone know how it got the name "American death triangle". It's a stupid way to rig an anchor, but, hell, we yanks are no more stupid than, say, the French.

[Fromage]

Actually, Pedestrian, despite the notorious methods and ethics of the French, the American Triangle is a remarkably stupid invention by the Yanks. I remember reading in John Long's "Climbing Anchors" that the AT was popularized among Yosemite climbers in the 1970s. I witnessed all sorts of surprising things in France and while I generally feel safer climbing in this country, seeing the occasional American Triangle reminds me that even folks over here make dumb mistakes from time to time, only not quite as flambuoyant as the French.

 

Vive la Raclette!

 

[pope]

quote:

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Originally posted by Paul detrick:

You guys are missing the point, its not the best way, it's easy to have one piece of webbing for one bolt, equalize the anchors, do what you will but I will allways change it.

---

I'm not sure how to equalize with "one piece of webbing for one bolt". If each bolt is clipped to an independent runner which joins the other at the power point (as you seem to be describing), the system doesn't really equalize. In fact, if the runners aren't exactly the same length, or if the pull is slightly off center from the fall line, then one bolt does almost all of the work. An "American Triangle" with a long enough runner (to keep the bottom angle small) is a much better solution since it equalizes.

 

A better system than either of these uses two slings which are clipped to both bolts and then clipped across the "X" at the power point. Consult a manual on anchor building for this equalizing system. This is pretty hard to describe and easy to screw up (one of Washington's very best rock climbers nearly died his first season when he attempted to rig this system for a top-rope but failed to correctly clip the "X"...he fell 35 feet into the talus). The only flaw in this system is that if the bolts are amply spaced, the V-shaped system may result in a bottom angle that is too obtuse (remember: the smaller, the better).

[Paul_detrick]

I use that system when i'm climbing more than one pitch, but use one long runner cliped to both anchors than clip the x. But if you don't want to leave any booty, you have to re tie your knots on anchors, and its not that hard to tie two water knots the same size.