Hanger Type Preferences/Safety

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Hanger Type Preferences/Safety

Postby hunter » Apr 9, 2007 7:32 pm

Hey all you vertical types, a question that came up as my girlfriend was reading through Alpine Caving Techniques (ACT) 3rd edition. In ACT they make the case that bent (normal to me) hangers are not that great and suggest that rolled hangers should be used on vertical walls and that clown hangers should be used on roofs. They further state that normal hangers should never be used on roofs. So, my question is, what hangers do you use when (and why)?
I'm asking this because I exclusively use normal hangers (or glue-ins which is a different can of worms) and am mulling over if there is a strong reason to change in some cases. The main reason I use normal hangers is because they are cheap in stainless (1.50$ or so each). I also think that the safety of normal hangers is well supported by anecdotal evidence from climbing (they just don't fail), at least for fall type loads.

James
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Postby LifeOnALine » Apr 10, 2007 5:51 am

For 'Normal' I guess you mean hangers of the Vrillee design like below:-

Image

They're perfectly fine when loaded in shear (parallel to the rock), but potentially lethal when loaded axially (pulled outward). In a roof you're of course pulling axially.

The problem is that for M8 bolts (or rather the sleeve the bolt screws into) when you pull a Vrillee axially there's a massive levering action from the hanger. Bolts snap, hangers snap, or rocks explode. Rock climbing bolts, at least for permanent installs, tend to be M10 or M12 and so a little stronger. Still not perfect though!

The Clown-style hanger tries to remove the levering effect by allowing the rope to wrap around the bolt, so giving a direct pull - so the Clown is ideal in a roof provided the anchor is OK. Clowns in shear against a very smooth rock are a teensy bit worse than Vrillees as there's now a lever action on the bolt, but on 'lumpy' rock the edges of the Clown dig in and prevent the hanger from sliding (like leetle baybee crampons :) )

If you want a demo of what can happen when you axial-load a Vrillee, take a look at the last row of the table at

http://www.lifeonaline.com/research/01/

~DM~
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Postby chh » Apr 10, 2007 8:13 am

That's interesting stuff. I noticed that the torque pressure was only listed on one trial, and it seemed low to me, but I can't be sure as I've never torqued that particular kind of bolt before. Were all bolts torqued to their specified levels? And what kind of rock was that? Either way, surprising results. Way lower than I had expected. Thanks for posting that. I've taken some falls on a Vrillee type hanger in a ceiling. I believe the bolts were M10 or 12, but either way my whips were not enough to dislodge it. It WAS however later chopped and the route was closed. I heard it was as a result of an accident, but I don't know for sure. The levering action does make a lot of sense, I'm just surprised at how low the pull outs were, particularly the last one.

Thanks again for the info.
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Postby hunter » Apr 10, 2007 10:30 am

LifeOnALine,
Yep, that's what I mean by "normal". I only use that terminology because they are what I see in use 99% of the time...

Quick question, what exactly is the definition of the M labeling system? (M8 vs M10) Is this just the diameter of the hole required?

Thanks for the info. Very interesting failure data. I think I now understand why ACT pushes so strongly for the clown, it is due to the type of bolt. I normally use bolts like these : http://www.confast.com/products/thunderstud-anchor.aspx (stainless 3.5in usually). The manufacturer only has specs for concrete but for harder concrete the tension failure is > 5000 lbs so I guess the overkill is enough even with leverage. I've seen these placed on horizontal roofs in limestone for climbing where they take hundreds of falls (usually not more than factor .5 or so) and haven't heard of a problem yet (except corrosion failure which is different).

I've always sort of wondered, why many cavers use drop in type anchors so much? It seems to me you are drilling a larger hole than is really necessary.

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Postby Mark620 » Apr 10, 2007 8:06 pm

chh wrote: I'm just surprised at how low the pull outs were, particularly the last one.


I am not surprised at all by that last one, a lever goes a long way in magnifying the forces.
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Postby l lambert » Apr 15, 2007 8:27 pm

Rock climbers in the States are trending towards the wedge anchor like the one hunter linked to. The hanger shown is not made to be loaded in tension. There are many brands of hanger that are made to be loaded in tension as well as shear i.e. the Petzl coeur. Leo
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Postby chh » Apr 17, 2007 7:57 am

L Lambert wrote:Rock climbers in the States are trending towards the wedge anchor like the one hunter linked to. The hanger shown is not made to be loaded in tension. There are many brands of hanger that are made to be loaded in tension as well as shear i.e. the Petzl coeur. Leo


I've seen my fair share of wedge anchors outside, but they usually have petzl or fixe hangers on them as far as I can remember. I didn't see hangers in that link that hunter posted. And the anchors themselves did have shear ratings at the bottom.
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Postby hunter » Apr 17, 2007 4:45 pm

Guess I wasn't clear on that. I was thinking mostly about the bolt since that was what failed in all the tests. The brand varies but in general I see either metolious type or fixe hangers on horizontal roofs and I've put up both.

The top hanger on this link: http://www.fixeusa.com/hangers.htm
or http://www.metoliusclimbing.com/bolthangers.htm

I've seen one or two of the old SMC hangers on steep climbs as well and they are often badly bent.

I can see that these hangers apply some leverage to the bolt but it doesn't seem to have led to many failures.

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Postby l lambert » Apr 17, 2007 9:23 pm

Either one of those bolt hangers is bomber as well as the petzl hangers I mentioned. I've personally taken some fairly long trips on the coeur while rock climbing. The type bolt used is more likely the main focus. Is the usage static loading or do you need a dynamic belay? In other words are you rappelling off of it or climbing past it? The bottom line on the SMC hangers is that they are not made to be loaded in tension and should not be used that way regardless of price.
Reminds me of the Whitesides climbers that loaded up on plumbers tape for hangers. It was all good as they ran it out on 1/4 inch split pins. Ahhh the good old days!! Leo
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Postby ljthawk » Apr 21, 2007 8:50 pm

When I was helping the SCC (Southeastern Climber’s Association) with their anchor orders I was specifically asked to order the Petzl hangers for overhanging applications. The climbers liked them because the hanger shape better aligned the load with the bolt than the Fixe hangers. One experienced climber instructed to install the hangers “upside down” on roof applications.

Take a look at the seventh and eighth page of http://www.imdl.gatech.edu/ljthawk/fixe ... der_04.pdf for an illustration.

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Postby Francis » Jul 21, 2007 3:58 pm

I use ring hangers for places where the pull is outwards from the rock (ceilings etc.). I would have thought that they are the best as they don't have any bending moment on the bolt at all. They can also be used as ordinary hangers as long as the pull is along the ring and not across it.

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Postby Eric Wright » Jul 22, 2007 12:17 pm

hunter wrote:LifeOnALine,

Quick question, what exactly is the definition of the M labeling system? (M8 vs M10) Is this just the diameter of the hole required?


Yup. These are metric diameters, M8=8mm, M10=10mm, etc. See <a href="http://en.wikipedia.org/wiki/ISO_metric_screw_thread">this</a> for more detail on the metric iso diameter scheme.

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