american triangle alive and dangerous

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dangry

Trad climber
tahoma, ca
Topic Author's Original Post - Jun 15, 2009 - 03:33pm PT
I was out at Clark's Canyon this weekend, many of the old cold shuts have been replaced with "Mussy Hooks" or tow hooks. That's great and thanks to the folks for updating the anchors. But many of the anchors I saw had only one quick link, thus the hooks don't come to a single point. To me this looks a lot like the old "American triangle". With any rappel set the anchor is loaded inward at 180 degrees. In my opinion these new anchors are no better than the ones they replace. All should be lengthened to bring the hooks to a single point when loaded.
Am I wrong? Are these anchors "safe" or should links and chain be added to make them "safe". I understand someone has put out a lot of money and time changing out the cold shuts.
couchmaster

climber
Jun 15, 2009 - 03:36pm PT
2 questions:

1st) What do you mean by 180 degrees? Does this image below hint at what you are discussing? So the pull is straight across? OMG!


How many rap/belay anchors have failed due to "American Triangle". If even a single failure is known to have occurred, please describe just that incident. Anyone can play for this question.

I'm curious.
Rhodo-Router

Gym climber
a greasy pinscar near you
Jun 15, 2009 - 03:39pm PT
I'll give you a quarter if you can pull two bolts by lowering off a sport climb.


Find something else to worry about.
dangry

Trad climber
tahoma, ca
Topic Author's Reply - Jun 15, 2009 - 03:42pm PT
OK so this might not be a big deal considering the strength of a bolt. I'm just bringing up an observation and asking a question.
180 degrees or straight across from each other.
couchmaster

climber
Jun 15, 2009 - 03:48pm PT
No No, I don't mean to say it doesn't matter.

If it looks something akin to this below (with the addition of the Mussy Hooks, then it should be fixed and the folks who "upgraded" it should be clued in.

Better angle, more redundant:

Ksolem

Trad climber
Monrovia, California
Jun 15, 2009 - 04:04pm PT
Pic #1 above is so wrong in so many ways...

Two mussy hooks or shuts across from each other are fine. For top roping, clip a runner or long draw into each one to make your center point. Last climber strings the rope through both anchors and raps or lowers.

Sure, the rope goes straight across, but there is no force multiplier, just some inward pull.

This should be Locker's cue:

Yer gonna die!
Mighty Hiker

Social climber
Vancouver, B.C.
Jun 15, 2009 - 04:08pm PT
Both examples are wrong. The first, because the bolts are too close together, and because of the force geometry of the chains. The second, because the bolts are too close together, and in what appears to be in a partly-detached block.

The rock in 'sport' climbing areas is often suspect, and belay bolts in such areas placed too close together.
dangry

Trad climber
tahoma, ca
Topic Author's Reply - Jun 15, 2009 - 04:21pm PT
coachmaster, yes once the hooks are loaded for rappel the hooks are drawn inward at each other.My understanding of the physics of anchors mean each bolt is taking more than 100 percent of the load. I'm by no means an expert. Nor have I heard of the American triangle causing a belay anchor to fail. I have read in several "how to" books that rigging an anchor in the "American Triangle" is not "bomb proof".
And of course any rappel anchor at a sport crag you add your own gear to TR through, any anchor given enough time can be sawed through.
Ksolem

Trad climber
Monrovia, California
Jun 15, 2009 - 04:26pm PT
The big problem in pic 1 is the rope being strung across the chains. I think it looks like there is a spare link over by the right hand bolt which is the intended thread point? Less than ideal, but not suicidal as shown.
kev

climber
CA
Jun 15, 2009 - 04:30pm PT
Ksolem,

Yeah I saw the first pick and thought WTF.

kev
Evel

Trad climber
the cliffs of insanity
Jun 15, 2009 - 05:49pm PT
Most sport anchors are in fact a form of the American Death Triangle. Two cold shuts, Two Fixe rings, pretty much all two-bolt horizontal set-ups are not correct.
A vertially aligned two bolt anchor is the way to go.

jstan

climber
Jun 15, 2009 - 08:18pm PT
Chains have the property of not stretching much under load. So if a horizontal chain link is tight you get force multiplication as 1/sin(ø) where ø is the angle of deviation from a straight line. For a 160# person the dependence of total force on angle goes as:

10 deg 500#
5 deg 900#
1 deg 4600#

That is with body weight. If you hold a 1000 # force in a fall you are talking close to 15 tons for 1 degree.

Everyone knows this but the facts did not seem to come through clearly in the posts.
Clint Cummins

Trad climber
SF Bay area, CA
Jun 15, 2009 - 08:41pm PT
[referring to anchors with 2 bolts at the same level with Mussy/tow hooks or Fixe double ring hangers, the original post]

Not a triangle (if you are lowering).

Not dangerous.

It is a triangle if you are rappelling, but the angle is likely under 20 degrees (see couchmaster's diagram) and gets close to zero quickly. Forces too small to be dangerous.

The "vertically aligned" bolt type anchor is nice for some things (like minimizing friction when pulling the rope). It requires more chain to create, though (assuming the bolts are a "safe" distance apart - at least 2 times the depth of the holes). It is not so good for a hanging belay with 2 people hanging there - some horizontal separation is nicer for that situation.
Greg Barnes

climber
Jun 15, 2009 - 08:50pm PT
Like Clint said, no worries. But there is a worry about adding chains to Mussy hook systems:

You have to watch out for the back side of the gates on Mussy hooks - they can shred rope sheaths. This is basically only a problem on anchors on slabby rock - but many at Clark are just that (even when the climb is steep). So the location and spacing of the bolts can be very important. With a chain added in, even if it is done correctly, if someone clips a Mussy hook on the end of a twisted chain, it might force the rope over the sharp back side of the gate. Do NOT go adding chains to Mussy hook setups unless you know what you are doing.

Also, if you are at some area such as Area 13 where you can lead one route and go clip the anchor of another to TR the other route, use your gear not the Mussy hooks to set up both anchors (which you ought to do anyway). In other words, if you clip more than 2 Mussy hooks (2 at one anchor, then 1 or 2 at the other anchor), the backside of the gates of the inner Mussy hooks can damage the rope sheath.
lightboi

Trad climber
MN
Jun 15, 2009 - 09:24pm PT
In the rock and roll world we often have to suspend a point somewhere in space. Tools such as this rigging calculator

http://design.cablepick.com/rigging

help make the math easier

It translates very well to climbing anchor loads. One can see the relationship of angle to load as well as different length of legs(ie making the chains different lenghts.

enjoy!!!
couchmaster

climber
Jun 15, 2009 - 09:27pm PT
Hold it hold it Greg. I've never used Fish's hooks, never even seen them in action, what are you saying there again? I can see that a rope could possibly be damaged on the back of the sharp gate, and that if you add a link to the equation it would turn the hook sideways (so add 2 links, not 3, 4 but not 5 etc. Additionally, the act of adding chains will make the possibility of a hook turning sideways, and thus causing a rope sawing action, increase. Whereas in the configuration shown in the picture, it is relatively stable, add more links and it gets floppy.

Is that what is being discussed?


From Fish's site: http://www.fishproducts.com/catalog/bolting.html

To Dangry, I can see that most likely, the hooks are NOT 180 degrees and pulling directly into each other. As John Stanard says if I understand him, there is less force on a non-static ( webbing) application as well. In fact, you can look up and get a calculation on this, but be aware that decreasing the spacing of the bolts so that the hooks touch together as you would like, will at some distance, decrease the strength of the wedge anchors. There is a trade off going on here you need to be aware of. This from the Thunderstud site, you can fish around for similar info. They are not saying that a 1/2 x 7" anchor that is 4" from another anchor has a bigger NET reduction in force than a 3/8 x 3" or 1/4 x 2", as the 1/2" diameter anchor is still significantly stronger, but the percentage of strength reduction is higher. Not knowing what exactly you are looking at, nor the depth and diameter or brand of anchor that was utilized in the replacement, I can only guess what the installer was thinking, but I bet you are better than good in this application.

"The forces on a ThunderStud® wedge anchor are transferred to the material that it is installed in. If the anchors are installed too close together, it can cause an interaction of the forces, thus reducing the holding power of the anchor. As a rule of thumb, the concrete anchor industry has established a minimum standard of ten (10) anchor diameters for spacing between anchors and five (5) anchor diameters from an unsupported edge. When vibration or sudden impact are part of the load condition anchor spacing should be increased. "

You can look around and get various Mfg actual numbers.
Majid_S

Mountain climber
Bay Area
Jun 15, 2009 - 09:32pm PT
this place is worse than RC.noob
Jaybro

Social climber
Wolf City, Wyoming
Jun 15, 2009 - 09:33pm PT
We're all gonna die. check this sh#t out and do the best for everyone each time. who does that?
jstan

climber
Jun 15, 2009 - 10:39pm PT
Speaking as an RC.noob.

The original placement was fairly clearly installed by someone who is not aware of the tradeoffs. If that is the case why are we to presume the bolt installation itself was not similarly poor?

By its nature rock is highly defective. When two bolts are close together the strain fields from each may well inter-react and will do so in the presence of defects. This is what leads to material failure.

In my post above one thing I was saying is that since nylon stretches, if nylon is in the system you will not have such small angles and such large force multiplication for two horizontally placed bolts. With chain, what you see is what you will get.

Apriori it also makes little sense to place two bolts in any piece of rock that appears to be separate from its surroundings. You think you have redundancy. You could be surprised.

Anyone aware of current emphasis being placed upon personal safety and who then goes and installs a personal safety device is depending upon remaining anonymous or upon the fact they and their family are both dirt poor.

I infer from this that it will take only a few egregious equipment failures to cause a radical change in currently accepted practices.

If it comes to this, it will not be pretty.
couchmaster

climber
Jun 18, 2009 - 02:17pm PT
Thanks John, since there is no pictures detailing what the OP is discussing at Clarks,nor any route names or corresponding collaboration, I was thinking that given the OP was saying that there was a 180 degree pull, and that he wanted the Mussy hooks to be touching, that in fact it was not a 180 degree pull, but instead the spacing is far enough that the rope runs through both hooks straight across.

If this is the case, and we do not really know, then it's probably not a 180 degree angle at all as Ksolem suggests on the 4th post or so. Looking at the picture and visualizing what Greg noted above as well, adding a second link would turn the hook so it would parallel the wall/trap the rope, and the attendant issues with that.

This should give us all pause and prod us all to remember that each placement that we come across was and is an individual and potential iffy proposition. There are a few places where this is not the case (say Beacon Rock where Joseph replaced each and every rap anchor with a rock solid brand new installation containing identical materials, cataloged and detailed what he did publicly, and left a brass washer stamped with the replacement date on each one so future generations have some information).

Any info on this from anyone else? Pictures or drawings?
Messages 1 - 20 of total 36 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
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