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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 11:02pm PT
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Nature,
to get a cone fracture pull collinear to the bolt z-axis--a tension load. Sometimes the bolt just pulls out and the rock stays intact, except the borehole is a little bigger.
Yes. pull on all 3 in tension and you'll be more likely to get cone fracture the closer triangulated they are.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 11:54pm PT
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right you are Banquo, the closest bolt should be 2 depths away with my remembered rule-of-thumb, so that would be 5" spacing for a 2.5" deep hole.
and I totally agree about the engineered solutions being different than our application, the fasteners are designed to be put into concrete with specs on the concrete... we put our anchors into rock of unknown structure.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 11, 2011 - 08:27am PT
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Ed,
start thinking in vector and tensor space, not these one dimensional simplifications. This is what I've been trying to tell you:
From the words of Bnaquo:
Your test loaded the bolt in shear. Spacing perpendicular to the direction of load doesn't matter much for groups of bolts in shear. It matters some if the the load is in line with the bolts. For shear the critical distance is to an edge or crack in the direction of load.
My words: Spacing of bolts is not of great importance when they are shear loaded to the extent of forces encountered on sport climbing anchors. Nevertheless, quality of rock must be accounted for.
Furthermore, I contend that rock quality is not this big unknown that some in this forum like to speak about. The pitch of hammer tapping on potential anchor sites reveals most of the information as to soundness of rock and perhaps only {tenured} experience and intuition can unravel this noise to make sense of it. Are you Tone deaf?
I am going climbing today. It is forecast to be 60F, 100 miles east of here in this Wyoming Siberian Landscape.
It has been a great chat. Thanks for the mental stimulation.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 11, 2011 - 12:13pm PT
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are you tone deaf?
yes, but I think I can hear the sound of poor rock under hammer taps...
and most of what I drill here is great granite, so the problems of "rotten rock" are usually not an issue, unless very large sections exfoliate off, but that isn't detectable via hammer taps.
as far as "vectors" are concerned, much can be learned by a simple reduction of dimension, say to 2, to include the effect of rotational forces on the rock in which the bolt is embedded. And even cracking in those two dimensions can capture some of the issues regarding the security of the bolt placements.
forces perpendicular to the bolt shaft can be analyzed by considering the rotation of the bolt about it's center, say half way between the bolt's end and the hanger. The force compresses the rock under the lip of the hole, and put's the surface above the bolt into tension. On the other side it is reversed, the bolt's end puts the rock above the bolt into compression, and the rock under the bolt into tension. The combination of compression and tension above the bolt is the cause for "blowout" if I understand these things... if the bolts are spaced by some amount the forces do not effectively add, but bringing the bolts in closer could cause problems. If the rock is fractured there are more problems, and many of those may not be diagnosed by hammer tapping, though that is all that we have. Knowing the rock you're drilling in is probably the best insurance for putting in good anchors.
when you are loading the anchors with just body weight I can't imagine the spacing of the bolts being an issue when the bolts are placed in sound rock. Just remember the picture of Dale Bard looking at the RURP anchor...
On multi-pitch climbs the anchors have to hold potentially much higher forces, and there the spacing could be an issue... once again, I am sure that there are types of rock and placements that the closeness of the bolts would not be an issue.
But in addition to the question of placement, one has to consider the issue related to a climber coming upon an anchor and deciding whether or not it is competent. The climber assumes that the FA team put the stuff in correctly, but how can it be judged? Standards at least help identify "good practice" and allow the climbers to decide without the benefit/need of talking to the FA team regarding the specific anchors.
All in all, it is why setting up your own anchors rather than using existing anchors is a better way to go... where possible. At least the responsibility and the nature of the anchors are known to you in that situation.
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Paul Martzen
Trad climber
Fresno
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Apr 11, 2011 - 12:46pm PT
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This website from Australia describes a number of very interesting tests, though all in sandstone. They do a bit of direct pull out tests and do get rock failures with interesting shapes. Some of the photos show failure cones that are not very conical, but very wide and irregular shaped, where plates of rock broke loose.
http://routes.sydneyrockies.org.au/display/thelab/Home
Different materials might have very different failure modes.
What I really admire is when people decide to test stuff as best they can with what they have available. I think that is not only educational in often surprising ways, but really fun. Inspires me to get back to some of my own testing projects.
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Mighty Hiker
climber
Vancouver, B.C.
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Apr 11, 2011 - 12:58pm PT
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Sort of on topic, I had a tour of a climbing equipment manufacturer's facility once, and was told that the most popular part of the tour is where you bust things in the test apparatus. Our internal imps seems to like it.
And real-world testing is always a useful thing, and something we can learn from, although the boundaries between what works, what is safe, and what is reasonable aren't always clear. Context can be so important, whether its the nature of the area (remote, popular...), or of the rock generally or specifically.
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Banquo
Trad climber
Morgan Hill, CA (Mo' Hill)
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Apr 11, 2011 - 03:10pm PT
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The sandstone is a non-isotropic material as pretty much all rock probably is. Stone masons and arrowhead knappers study the structure of rock to take advantage of this.
What you need to take away from these discussions is that generalities about bolt strengths are probably unreliable more often than not. People love rules of thumb but they just aren’t very safe when it comes to structural capacity. Be very conservative in your bolt placements use the longest fattest bolts you can and space them as far apart as is reasonable.
When I teach students how to design or analyze structures they would really like to be able to design them “by inspection” not by engineering but heuristic design just isn’t reliable. Heuristics are very valuable in streamlining the design or analysis process but shouldn’t be the sole basis for engineering conclusions or decisions. Another common weakness in design reliability is the logical conundrum that it requires competence to recognize competence, i.e. you cannot evaluate your own competence. In other words, when you start to think you know your stuff, you better double check. Confidence is not competence. If people suggest you might not know what you are talking about, listen up because they are likely being too kind.
“Among the Inept, Researchers Discover, Ignorance Is Bliss” NY Times 2000:
“There are many incompetent people in the world. Dr. David A. Dunning is haunted by the fear he might be one of them. Dr. Dunning, a professor of psychology at Cornell, worries about this because, according to his research, most incompetent people do not know that they are incompetent. On the contrary. People who do things badly, Dr. Dunning has found in studies conducted with a graduate student, Justin Kruger, are usually supremely confident of their abilities -- more confident, in fact, than people who do things well.”
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klk
Trad climber
cali
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Apr 11, 2011 - 03:16pm PT
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i.e. you cannot evaluate your own competence. In other words, when you start to think you know your stuff, you better double check.
good luck with this message.
of course, if you actually persuade STers that it's true, this forum will basically have to shut down or else limit itself to the occasional climbing thread.
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tarek
climber
berkeley
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Apr 11, 2011 - 03:51pm PT
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OP wants to restrict this to his narrow topic. Fine.
But climbers are much more interested in single bolt strength on lead, where fairly often you are facing death or injury if a single bolt fails.
Toprope/rappel anchors should be bomber, and if not, made so.
If a cold shut is wearing through, just replace it, or _.
Anyhow, took a quick look at MH's link. Here's another log on the fire:
The test results for staples were not published by the DAV as far as I know but we made and tested some. 8mm dia rod with 80mm legs achieved around 6 to 8 kN, When I knurled the legs to improve the bond the rock failed, generally at around 12kN. Examination of the failure showed that drilling two holes so close together seriously weakens the rock, according to friends in the quarry industry the drilling produces micro-fractures and these link up producing an area of shattered rock between the holes.
http://www.bolt-products.com/Glue-inBoltDesign.htm
So, how you drill, matters.
[edit: might matter]
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cragnshag
Social climber
san joser
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Apr 11, 2011 - 04:22pm PT
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Nice shear cone! Looks like for that crap rock you will need to limit your weight and length of fall. Still, 8KN-11KN isn't all that bad. Time to go on a diet folks.
I'm glad I climb on granite.
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couchmaster
climber
pdx
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Apr 11, 2011 - 04:45pm PT
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A lot of the Aussie and other tests of various sandstone show that correct combos of bolts and glue will garner a CE rated placement of 26kn or better.
Bolts just are not often failing in the field anywhere in the world that I can see. In fact, the link up thread: wherein some OLD carrots were tested (essentially a 5/16" diameter sized bolt slammed into a tight hole, no glue) held 25 kn.
BTW, love the tests of all the nuts and cams as well up on that thread link, good stuff!~
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 12, 2011 - 07:07pm PT
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This website from Australia describes a number of very interesting tests, though all in sandstone. They do a bit of direct pull out tests and do get rock failures with interesting shapes. Some of the photos show failure cones that are not very conical, but very wide and irregular shaped, where plates of rock broke loose.
http://routes.sydneyrockies.org.au/display/thelab/Home
For the sake of making the best use of human energy (like packing test equipment to some cliff) our experiments serve us best when we test bolts in modes replicating loads in same fashion that we as climbers would load them, i.e. in lead falls or belay/rappel anchors. The preponderance of top rope and belay anchors are on surfaces near vertical and would get predominately shear loading. To axial test bolts anchors when we are shear loading them in real life gives inapplicable results for this situation and probably a somewhat lower force than if the test had been done for shear loading.
All measurements are local.
These tests may be like determining how hard it is to pull off your bumper(tension) and then from that measurement complaining about how unsafe your bumper will be in a collision (compression).
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