Best Rap Anchors?

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WBraun

climber

Nov 22, 2009 - 02:16pm PT

hand drilling times be for half inch bolts

Horrendous, bring your lunch.

Greg I don't know who to talk to other then Jesse would know the powers to be above.

From your last post it sounds like a bureaucratic nightmare.

The only real legal exempt status is Rescue.

Clint Cummins

Trad climber

SF Bay area, CA

Nov 22, 2009 - 02:22pm PT

Jim,

Thanks for sharing your insights on cone failure of concrete vs. natural rock. Especially for sandstone, where the (wedge) bolt fails by pulling out rather than causing a cone failure. I wonder, though, how the 5-piece sleeve bolt (Power-bolt) with its higher pullout strength compares with the wedge bolt in sandstone. In sandstone, I presume they both fail in pullout without a cone failure (unless it was wet or something).

I am feeling better about my use of 3/8" stainless wedge bolts on new routes. (Of course, most are so obscure, they are unlikely to see repeated falls). But I also like the concept that the bolt will start to look bad before failing, in cases where it has taken a very large number of falls.

Greg,

Thanks for sharing your experiences and thoughts on 1/2" and power drilling. I agree that power drilling disrupts wildlife less than hand drilling, because it the noise is so brief. (This is for a fixed number of holes, so it assumes the context of replacement; when in developing new routes, power drilling is likely to increase the number of holes and routes being drilled). And thanks for clarifying about power drills not being permitted in Wilderness of Joshua Tree.

P.S. Roger has a new way to drill out the 5/16" holes for 3/8". After you extract the 5/16" buttonhead, you turn it 90 degrees and pound it back in! Then you extract it, turn it 45 degrees, repeat. After this process, it is apparently a lot easier to enlarge the hole to 3/8".
And for extracting the 5/16" in the first place (I think you know this trick, but others may not), you use a special tuning fork or knifeblade pitons to get it out until resistance is very high, then you pound it back in and repeat. I guess this loosens the crumbled grains around the bolt from the extraction process.

JimT

climber

Munich

Nov 22, 2009 - 03:02pm PT

Thanks for the compliments, back from my first bouldering trip to the indoor wall this year so trashed! No place for old men!!!!

Torquing throughbolts is a bit of a funny topic but since you guys are into the techy side here goes.

In Europe (where they where developed) these are technically called `torque controlled anchors´and get a seperate ETA (European Technical Approval) number from the more usual multi-piece (this is called Option 7).
For critical fastenings the old system was that anchors had to be on-site tested after installation which was slow and expensive, especially if they failed and had to be replaced. The solution was an anchor where the installation tested the pull-out resistance at the same time and this anchor is the wedge or through bolt. The specified tightening torque is a test against pull-out and nothing more, in most applications they are in fact torqued-up to check they hold and then released to install the object as most profile sections won´t take this sort of pressure.
The torque is chosen to give a load of 4 times the installed working load (the typical construction industry safety factor).
For a typical 10mm bolt the tightening torque recommended is 24Nm to 30Nm which represents a pull-out force of just over 20kN.
For a 12mm then around 50Nm which is a pull out of ca 40+kN.
(all these figures vary a bit depending on the manufacturer).

So to put it simply, if the bolt takes the required torque then it will hold what it says on the packet, if it won´t take the torque then it isn´t holding.

You can obtain the screw pressure for any bolt/thread from something like Machinery Handbook or any thread spec table if you need to work out the torque for say a 16mm bolt in sandstone where you can´t apply the full torque (100Nm) but still want the 20kN pull out, (15Nm was what we used in the end).

Under torquing- doesn´t do any harm but hasn´t properly controlled the bolt
Over torquing- the danger is weakening the bolt and for a 10mm bolt the over-torque is ca 35Nm.

And does it all really matter? We installed 30 80mm X 10mm bolts in identical conditions and rock, 10 were torque and released, 10 were torqued and left pre-loaded and 10 were just hammered in but never tightened, then they were axial (straight out)pulled
The first two cases were effectively identical, the never-torqued versions were marginally stronger by an average of 5%.

Beer time!!

Jim

Greg Barnes

climber

Nov 22, 2009 - 03:06pm PT

Hey Clint, yeah I'm the one who suggested the 5/16" pulling trick (pull it out a bit, pound back in, repeat). It's still a big pain regardless! Neat trick on the enlarging to 3/8" hole, but of course it depends on the rock quality (if the 5/16" is too compressed, wouldn't work).

Yes, the power drill exception would have to be based on the replacement of a fixed number of old bolts, and I bet any permit that might happen in the future would be on a route-by-route basis. But this is all up in the air for now, not much chance of it happening anytime soon.

As far as drilling times for 1/2", I have to admit that the very first bolts I ever placed were two 1/2 x 3.75" 5-piece bolts, in granite, with a hand drill. Took about an hour and a half each. I learned really quickly why you don't hand drill that size in granite! (it was a top anchor on a ground-up route, and I didn't have any other bolts, and I wasn't going to rap off a single bolt). And that wasn't Yosemite-quality granite either...

Hummerchine

Trad climber

East Wenatchee, WA

Nov 22, 2009 - 03:24pm PT

One more question for the bolt experts out there (and thanks again for all the great info!):

Is there any way to remove Fixe wedge bolts (or similar)? A number of years ago I foolishly purchased a Bosch and a bunch of Fixe hardware. I say foolishly, because I can count on both hands the number of bolts I've placed in the last 30 years. I think I figured, hey, I'm way into climbing, I need this stuff! Unfortunately, I just don't have the time or motivation to equip new routes; I have replaced a very small handful of anchors, will likely do the same in the future. (my neighbors love me, they have borrowed the Bosch for home projects). So I have done some crude testing on the Fixe wedge bolts. Man, those babies sure seem bomber! I tried to remove one; beat the crap out of it with a hammer, tried to break it with a breaker bar, cut half way through it with a hacksaw and beat the crap out of it some more. With more cutting and hammering you can eventually cut/break them off. I'm way impressed with their strength, but unless I'm missing something there is no way to cleanly remove one. Which makes me think, that even though they are bomber, I should not use them. It just seems so clearly desirable to be able to remove and replace them way in the future, possibly with a larger bolt. Anyway, is there any trick to removing them?

Thanks again!

cragnshag

Social climber

san joser

Nov 22, 2009 - 03:43pm PT

Bruce- I agree that most bolts out there (on vertical to slabby rock) will exprience a shear force perpendicular to the axis of the bolt- certainly all the bolts I clip anyway. For folks clipping bolts on overhanging rock, then pullout strength/ shear cone is the what governs.

I believe the vast majority of ground-up bolts in Yosemite fall into the first case, thus really we should be worried about bolt shear. Since the bolt shear is primarily just a factor of bolt diameter, the bolt spacing is irrelevent.

In reality, a hand drilled bolt will also experience a little bending stress since there is almost always a small amount of cratering at the lip of the hole. Of course, this is a such a small effect, that it can be neglected. Now if that hand drilled bolt (in vertical rock) takes a huge loading (much greater than what we climbers can generate), then there may be some localised crushing of the rock at the lip of the hole that encourages more bending. When the bending stress exceeds the elastic yield stress of the bolt, the bolt will deflect slightly in the direction of the load. Then some the shear loading becomes pullout loading due to the new direction of pull. But not a big deal because a good bolt can handle this newly introduced load without issue. As long as the bending of the the bolt takes place in the eleastic region of stress, the bolt will spring back to it's original shape. With an even higher load, the bolt will behave inelastically have permanent some deformation in the direction of the load. Thus subsequent falls on this bolt will always involve some amount of pullout loading, albeit small.

A couple years back Banquo and I tested 1/4" x 1" concrete screws in a good granite block using a load cell. The bolt was oriented in the block to simulate a dead vertical placement. We found that at about 1800 lbs of force perpendicularly to the bolt hangar, some local spalling occured at the lip of the bolt. This absorbed some energy and with initial elastic bending the load reading on the cell went down. We then continued to apply more force until we reached aroud 2000 lbs where there was permanent deflection in the bolt, and with the combination of the slight loading offset caused by the bolt hangar itself, created enough pullout force to yank the screw out of the rock. This is more or less what we expected since we wanted to test the screw's ability to bite into the granite. (Note: the screws were designed for concrete which is "soft" compared to granite and allows for more purchase of the threads). So the failure was a pullout failure at a load that would likely be a lot less than in concrete (you could actually calculate it based on hangar geometry, spall depth, etc, if so motivated). So in theory you could use these little screws on slabs but forget about it for vertical to overhanging terrain. I placed only one in real rock (a slab) and I plan to replace it with a 3/8" bolt.

Hey Banquo, I know you have photos and graphs and stuff about our experiment. I'm sure you can work in Mohr's Circle in there somewhere for the amusement of us Tacoeans.

Greg Barnes

climber

Nov 22, 2009 - 03:47pm PT

That's why we stopped using stud bolts of any sort - Fixe, Powers, Hilti, etc. They are not removable in the future. Breaking them off at the surface (by simply over-torquing them to death) is about what you can hope for, unless the original hole was too big.

Of course, the future is a long ways off for stainless stud bolts, especially those placed in the desert southwest. And if marine grade (316ss) are used, in combo with 316 hangers (like Petzls), then the corrosion resistance is pretty darn good.

Jingy

Social climber

Flatland, Ca

Nov 22, 2009 - 03:48pm PT

IDK.. the kind that stay put?

cragnshag

Social climber

san joser

Nov 22, 2009 - 04:03pm PT

Hey Clint,

Yeah, I've hand drilled concrete too. It can be easy or tough depending on the mix design of the concrete, Most concrete is just cement (essenitaly powdered instant limestone), sand, and aggregate. Depending on the type and concentration of the aggregate, it can be tough to drill. You stand a good chance when drilling concrete to drill right into a chunk of aggregate (granite in many cases, depending on location of batch plants, quarries, etc). Then it's like drilling into granite except harder because the cement/ sand matrix absorbs some of the energy of the hammer blows (as someone earlier pointed out). That's why hammerdrills drill through concrete like butter- they rely on much smaller percussion and high repetition- so that the stiffness of the matrix is not an issue.

I've got a quarter incher with one of Dan D's SS hangers (Leeper lookalike) on my concrete porch securing a wire that holds up the Bouganvilla. It was drilled from a great stance...

Banquo

Trad climber

Morgan Hill, CA

Nov 22, 2009 - 07:06pm PT

Cragnshag asked me to post this information and photos from 12-15-2007. We tested 5 (1/4"?) self tapping type concrete bolts installed in a new, split, rough granite block. The average ultimate strength of these was 2134 lbs with a standard deviation of 249 lbs. Using n=4 and 95% exclusion student's T distribution, I came up with 1444 lbs as a reasonable ultimate strength. For allowable I would use about 50% of that or ~700 lbs.

Needless to say, time, quality of rock, weathering of rock and bolt, quality of drilled holes, cyclic loading, etc. were not considered. Note that drill diameter would be critical. We tested shear strength only and have no pull out or combined load data.

We need some more details from cragnshag.

Brian in SLC

Social climber

Salt Lake City, UT

Nov 22, 2009 - 07:46pm PT

Here's the nearest thing to a stress cone type failure I've seen "in the wild":

At Cave Creek in Arkansas. Sandstone. The bolt placement was a 2.25" Rawl (Power) bolt with a Metolious hanger (sure about the bolt, less so about the hanger). A feller had clipped it, fell, and pulled the rock and bolt out in one swell foop. Was some 'net chatter about it a few years ago. Crazy to see in person.

I've seen similar when I've tightened a bolt in granite and cracked the rock through placement. Pulled the bolt and patched the hole. A couple years later, climbing the route, I kicked that hold and had the whole bolt placement area spall off (narrowly missing partner and gear/rope).

I personally really like those ring type anchors that Fixe, Faders and Raumer sell. Compact and they seem to wear well. Spendy in stainless, but, less to worry about long term and they are replaceable.

Great info!

-Brian in SLC

Banquo

Trad climber

Morgan Hill, CA

Nov 22, 2009 - 07:59pm PT

I work in and teach structural engineering. I believe that the single key factor that allows for the success of steel reinforced concrete is that the coefficient of thermal expansion of concrete is very close to that of carbon steel. If the coefficients of thermal expansion were very different, a composite of the two materials would cause the structure to tear itself apart during temperature cycles. It works because the two materials are compatible.

The Europeans seem to use more epoxy anchors than we do here in California. Does anybody know if much testing of epoxy anchors exposed to freeze thaw cycling has been done?. Anchors in the hot sun can be well over 100/°F and subzero temperatures certainly occur in alpine situations. In fact, these extremes might be seen in a day and many cycles might occur in the life of the anchor.

Coefficient of thermal expansion, microstrains/°C

Granite 8.5
Carbon steel 10.8
Portland cement concrete 8 - 12
Stainless steel 17.3
Epoxy resin 25 – 30

Steve Grossman

Trad climber

Seattle, WA

Nov 22, 2009 - 08:10pm PT

Banquo- Nice testing set-up!

What is your perspective on twist shear problems arising in stainless steel wedge anchor production during the thread cutting step for bolt diameters 3/8" or less?

healyje

Trad climber

Portland, Oregon

Nov 22, 2009 - 08:22pm PT

I wouldn't doubt for a second that the 2:1 distance:length formula and 'cone' perspectives in construction is due to the fact that concrete is a very active material which comes in a myriad of compositions. Further I would say the ratio of good-to-bad pours is also a consideration as plenty of mediocre and lousy pours happen even in the U.S. from time to time. Concrete isn't stone. I also don't doubt weak or chossy sandstone or basalt will 'cone'; but in good, solid rock - granite, basalt, and even sandstone (SE) - I don't believe it's a particularly valid construct for climbing and I've never seen evidence of it in all my anchor replacement work.

cragnshag

Social climber

san joser

Nov 22, 2009 - 11:05pm PT

Here is a photo of the concrete screw that we tested. It's the 2nd from the right. Pretty strong for their size, but difficult to twist into the hole if you are drilling overhead so I'm not using these. I'm drilling almost exclusively 3/8" and I keep a couple of 1/4" x 1" buttonheads handy for lousy stances.

Also shown are a carbon steel sleeve bolt, 316 SS wedge bolts 3/8" and 1/4"
a Powers 410 SS "Wedge-Bolt" 1/4" x 1 3/4" that is actually a concrete screw (not sure what idiot at Powers came up with the name since it does not look or perform like a wedge bolt), and a 1/4" X 1" recycled buttonhead, a standard 3/8" modern SS hanger, and Dan D's SS 1/4" homemade hanger.

Mighty Hiker

climber

Vancouver, B.C.

Nov 22, 2009 - 11:16pm PT

Thanks to everyone for all the information and discussion. Interesting stuff.

Edit: I liked that Jim T, after all the analysis, ended up saying his rule of thumb was to separate two belay bolts by at least one hand's width - for him, 23 cm. Very Olde English measurement!

JimT

climber

Munich

Nov 23, 2009 - 04:12am PT

Steve. We don´t have much to do with anchors less than 10mm because they can´t be sold in Europe. We tried with 8mm but they let go just under the standard at ca. 24kN
There are some wedge bolts coming out of a large Asiatic country which I won´t name which have poorly formed or even machined threads which tend to sieze up when they are being tightened, they are also made of some alternative 316 but just pass the norm tests. Still nasty though so we only buy European made stuff. Best by far are rolled threads and it is hard to believe anybody makes them any other way simply from an economic point of view.

For climbing walls the standard is EN 12572 and the test is 8kN for 10s on the first three bolts and the lower-off. The attatchment point (steel behind or whatever) should be specified to hold 10kN.
The first bolt may not be more than 3.1m from the ground and the spacing thereafter not more than 2.5m. What is considered an acceptable lower-off/top-rope point varies from country to country, one snapgate (for lowering) and a screwgate being pretty normal or a single ramshorn. In Germany and Austria it is usually required by the approval/testing body that the lower-off is two points joined by chain and that the top two or three draws are fixed and the rope used through these when lowering or top-roping.

Hummerchine- We drill out old bolts using water-cooled diamond core drills and then fit a glue-in, for a typical sport climbing venue this is easy if a bit slow but doing this on big routes would be a nightmare! Depending on the drill you have you get 5 to 8 bolts out per battery and need about 1 litre of water so a lot of hauling to be done. Doesn´t work by hand as the core drills are rotary not hammer (well, maybe with a brace and bit-I´ll maybe have a go at this this week but its going to be tough).

Banquo- The German alpine club did pull tests on these babies (known as Thunderbolts in most places). They suprised everyone by holding well and certainly got the required numbers but these were the 10mm version. However the difficulty of placing them halfway up a route hanging on a rope means they are totally impractical, 10mm and larger you really have to use a rotary hammer and the fixing tool. There is also some testing done by a guy in Australia which I might be able to find, he also decided the installation was too difficult to make them usable.

Re thermal expansion, fortunately the types of adhesive used are quite elastic and allow the bolt to change size without cracking or letting go, for really big bolts used in civil engineering there are special systems and dimensioning to cope with this but for us it is not noted to be a problem. Incidentally, while nearly everyone talks of using epoxy to fix bolts I doubt that 10% of the bolts actually use this but instead polyester, vinylester, modified vinylesters and the similar methyacrylates, in fact I´m probably the only idiot in the world that has fitted 2500 bolts with real epoxy!
Long term testing in the Alps show no difficulties with glue-in bolts and in fact the recommendation from the German Alpine Club is that bolt-ins are only to be considered satisfactory for 10 years and in areas of freeze-thaw only glue-ins should be used.
For real long term durability then quick setting cement is the way to go but you need bolts made for this and it is a bit fiddly to do on the cliff, this is the way the via ferattas and big belay bolts are installed all over the Alps.

Jim