Discussion Topic |
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Dingus McGee
Social climber
Laramie
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Topic Author's Original Post - Apr 10, 2011 - 11:20am PT
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Consult the photo "Test setup for 2 inch bolt spacing" to see test set up.
Consult the photo " Results of Pull test of Test setup for 2 inch bolt spacing" to view results. Results: NO BLOWOUTS
In general Your greatest problem encountered when putting bolts this close together will be dealing with the FLACK you will get from THOSE WHO KNOW NOTHING!!
An older Hilti product catalog claims a shear load of just under 5000 lbs for the 3/8" carbon steel bolt used in the test. For this test the nut was just finger tight so there would no Coulomb friction with the hanger against the cement.
How strong was the cement used in the test? It is quite old and has surface cracks here and there. Let's say 2500psi compression.
If you are placing bolts anchors (for your descent) in pumice stone which always has air pockets, shale layers, mudstone, unconsolidated sandstone, shattered quartzite, shattered limestone, gruss? (granite weathered to an extend that grains keep falling off when rubbing the rock) definitely choose a bolt spacing greater than 2 inches and then do a few "Hail Marie's" or get down on your Knees and Kiss your Rosaries. Either way you are likely to get DOWN.
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Studly
Trad climber
WA
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Apr 10, 2011 - 11:22am PT
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What route is that on? It looks vaguely familiar...
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 11:52am PT
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radical,
the intention of (rap) anchors is for rappelling and top roping. The loading from rappelling is your body wight. The loading a GriGri belayed top roping fall puts on a system is at least equal to the sum of the belayer and the climber (typically 200-500lbs). And then add the transient shock factor 1.5 times this. This result is considerably lower than 5000 lbs.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:05pm PT
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radical,
Rock is almost the antithesis of the uniformity you see in concrete
If what I think you are hinting at was true about "climbing rock" we would all be surfers.
Concrete starts cracking form the day it is poured and for less than a month the curing strength exceeds the cracking rate. Most climbing rocks are stronger than concrete.
The observation of Uniformity is not exactly a good measure of rock strength. Granite is a random mix. Shale mudstone may be quite uniform.
The comparative drillabilty difficulty of rock and surface crack observation generally give a good idea for assessment of rock bolting quality. Plus taping with hammer for that sweet sounding high pitch of good rock.
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Crimpergirl
Sport climber
Boulder, Colorado!
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Apr 10, 2011 - 12:25pm PT
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What are the advantages of placing bolts so closely together?
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Ksolem
Trad climber
Monrovia, California
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Apr 10, 2011 - 12:28pm PT
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So you only loaded the middle bolt?
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:30pm PT
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BJ,Regardless, your small spacing would affect the strength of your anchors deleteriously, and should not be used
It is important to note that I question your meaning of the wording "deleteriously", as the other two anchors are still quite capable of each taking a 5000 lb load. My test result are completely contrary to what you have stated. Start think before speaking and try making some cents?
Furthermore, the application of some ones general table for bolt spacing is non rational applicable of what we are trying to establish here.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:35pm PT
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Ksolem,
yes, only the middle bolt. Here is the line of reasoning about the failure path. Let's say the left coldshut is totally worn through and right one is likely to fail soon. When it fails the center bolt will have to perform. Get it?
There are many other loading failure paths we could design/test for but, for now I though this one was a good first run.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:38pm PT
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radical,
were are not arguing about all the types of rock encountered on a rock climb, but where an intelligent anchor bolting person would choose as his site for the anchor. Remember that high pitched sweet sound of solid rock?
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:40pm PT
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locker,
I hear ya. This is actually the neighbors garage slab apron that he is going to replace.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:42pm PT
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Crimpergirl,
in general there are none unless you are adding a safety feature between two bolts that have open cold shuts.
Consult further my posting: Is this the elegant solution to safe anchors?
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:52pm PT
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BJ,
when you make no sense you will get brotherly love from me but no girly sympathy.
in general the companies writing these tables wish to pass info to contractors using their products that will pass the stringent requirements for commercial construction. The safety factors they impose are far greater than what climbers need to make safety work for them.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 12:56pm PT
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there are "rules of thumb" for fasteners in concrete which are probably applicable to outdoor settings in rock, though experience is a good guide, one wants to avoid experience from accidents.
As a general rule, I have always thought that avoiding the "right angle" cone created by the anchor shaft with the height set by the length of the hole was the "keep out" zone for other bolt placements... more simply, if you drill a 2.25" hole, keep the other bolts out of the 2.25" circular radius centered on that bolt...
There are modern fastener "rules of thumb" for instance, from this site:
http://www.confast.com/products/technical-info/thunderstud-anchor.aspx
Concrete Wedge Anchor - Anchor Spacing:
The forces on a ThunderStud® wedge anchor are transferred to the material in which it is installed. If the anchors are installed too close together, it can cause an interaction of the forces, thus reducing the holding power of the anchors. 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.
I added the underline to indicate that static pull may not be the best test of the anchors... the "minimum 10 anchor diameters" for a 3/8" diameter bolt, would be 3.75" independent of the depth of the hole...
do a Google search on "9_Headed_Anchor_Design.ppt" and you'll get a really good presentation on the engineering calculations of a "headed anchor design" which is not what we have... but shows the depth of the attempt on the engineering specs that go into these rules...
unfortunately you cannot access the ACI or PCI standards for free.. . and there are none specifically written for our application, rock climbing anchors, but you can glean bits of information off the web...
Like HERE
while I agree that there may be a lack of specific test information available to the climbing community, it is really important not to over generalize specific tests because the actual strength of the anchors depends on the local rock (and that includes different rock on the actual route). Not every bolt placer has a PhD in engineering, so general rules will have to suffice, and those rules will be, by nature, conservatively stated...
bravo on the tests! it is an important contribution...
it would be even better if we could test anchors in real rock and with falling loads as would be encountered in our real lives!
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 12:57pm PT
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BJ,
you sling words around like a thoughtless Tea Bagger. The test is quantitative in that the "fuseable link" was the 3/8" hilti bolt, the bolt spacing was 2", tested force to drag my vehicle on a dry day exceeds 5400 lbs. etc etc. Furthermore on another test of 10 Hilti bolt I found the standard deviation to be 0.
Look up the meaning of quantitative testing!
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:00pm PT
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Hartuni,
the right angle cone is for bolts that are in tension force loading. Those with any sense will be careful to create situation where the load is a shear load and they will torque the nut.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:04pm PT
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Ed Hartouni,
consult further my included photo of the bolt failure. You will see a very small zone of concrete failure towards the line of pull. This does not happen when bolts are torqued to specifications.
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klk
Trad climber
cali
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Apr 10, 2011 - 01:09pm PT
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while I agree that there may be a lack of specific test information available to the climbing community, it is really important not to over generalize specific tests because the actual strength of the anchors depends on the local rock (and that includes different rock on the actual route). Not every bolt placer has a PhD in engineering, so general rules will have to suffice, and those rules will be, by nature, conservatively stated...
bravo on the tests! it is an important contribution...
it would be even better if we could test anchors in real rock and with falling loads as would be encountered in our real lives!
all of this is worth re-stating.
esp. since almost none of the sport areas i climb at involve vertical walls or good rock. steep choss if yr lucky. steep mud, often as not.
tilt that baby about forty or fifty degrees.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 01:09pm PT
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thus my cautionary statement regarding the lack of specific tests for climbing applications...
however, your tests are inadequate. In your anchor design, the middle bolt is loaded only if the one or both of the other anchors fails. If those anchor failures compromise the rock matrix, e.g. failure due to cracks, etc, the specific nature of the failure may compromise the middle bolt... and that outcome can be reduced by spacing the bolts further apart, at least that is my "intuition," it depends on the rock, of course.
there are specifics on eccentric forces on the bolts, the problem being, I would guess, that the rock away from the direction of the force goes into tension, which is not good for these sorts of materials, and the bolt then rotates out as the rock fails. This poses a problem for spacing, as the force comes on the middle anchor if one of the side anchors blows out, and the size of that blow out includes the rock that the middle anchor is depending on to hold.
only testing can tell us... so I'd encourage you to continue, this is important information and an important conversation... since I'm trained as a physicist my statements tend to be critical, though they are not meant to inhibit these sorts of activities, rather, to try to increase our understanding of the meaning of the test results
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:10pm PT
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Ed Hartouni,
"Sudden impact" a disclaimer for thunder stud.
We are talking quite relative gradients of force loading. Ash any belayer whether they would rather catch a climbing fall or or a car going at 10mph.
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Apr 10, 2011 - 01:10pm PT
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Garage floor or not, I can't believe you bolted that close to a crack.
Interesting discussion, carry on...
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:12pm PT
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Ed,
I could do about 10 of these test and establish some statistical significance.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:15pm PT
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Ed,
I will stick with the tests. I also know the theory quite well. I cannot comment on some of your wild speculations much!@ Like the "rock may get in tension etc"
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 01:16pm PT
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I don't think that's a wild speculation, it is just Newtonian force analysis...
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:21pm PT
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Ed,
It seems you have missed some of the previous chatter.
Consult further my posting: Is this the elegant solution to safe anchors?
In that posting I suggest putting a device between two less safe anchors while still preserving a "no untie anchor".
The two preexisting bolts may sometimes be as close as say 4 inches apart.
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Mighty Hiker
climber
Vancouver, B.C.
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Apr 10, 2011 - 01:21pm PT
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This is all quite interesting - the collision of physics with engineering with real world with community 'norms'. I tend to agree with Ed - such information as there is suggests a healthy spacing be used.
a thoughtless Tea Bagger Isn't it redundant to use "thoughtless" and "tea bagger" in the same sentence?
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 01:27pm PT
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for the purpose of full disclosure, I am among those who have used Dingus' sport anchors and I have absolutely no qualms about their security... and about the care that Dingus has taken to assure that these anchors are safe for their purpose
I especially like the "Ram's Horn" design, though it requires you to be able to understand concepts like "left" and "right" and so may disqualify some of our colleagues from safely installing them on routes
But sport anchors intended for top roping and lowering, for the most part, have a different set of requirements from those anchors on multi-pitch climbs that may also have to hold forces generated in high fall-factor falls, so it is not clear to me that the community benefits from any specific dogma concerning safe anchors
Also, we all depend on the anchor-placer to provide us with safe anchor placements, and we trust those anchors with our lives, literally... so more discussion is a good thing
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:28pm PT
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Ed,
so okay I will go along with the Newtonian physics.
Let's say the top of the borehole is 12 o'clock. The compression loading at the mouth occurs at 6 o'c and at 12 o'c in the back of the bore hole. At 3 oc and 9 oc at the mouth there could some resolving tension stress. But this is very small. In fact so small in my test that there are no signs of failure.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:36pm PT
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Ed and Mighty Hiker,
okay I will make known a failing in my description of my safe anchors statement!
It should have read: Is this the elegant solution for safe sport climbing Anchors?
The distance question arises when you get 2 existing bolts very close together.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:43pm PT
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Mighty Hiker,
There are a lot of posers out there. I once ask to speak to a Hilti tech engineer. The guy was not an engineer but at first said he was one. When he realized he could not answer my question he gave me the # of an engineer. This guy said he could only quote their manual. The info would help in the design of rock training course I was hired to build for a Summer Camp. I called my friend Tom Kelly a climber and rock engineering consultant and we hashed out a solution.
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High Fructose Corn Spirit
Gym climber
Full Silos of Iowa
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Apr 10, 2011 - 01:48pm PT
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The guy was not an engineer but at first said he was one.
I hate that.
And there should be a law agaist it.
Just as there is for doctors.
Damn it.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 01:52pm PT
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Ed,
I have heard physicist say "let's do a thought experiment." It certainly seems a lot of your speculation was a though experiment without much detail?
But though experiments hold no candle to seeing how bolt/borehole destruction really happens as loading occurs.
Is my loading too slow? I could drive the van against these anchors.
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Ed Hartouni
Trad climber
Livermore, CA
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Apr 10, 2011 - 02:02pm PT
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I've thought a lot about the "dynamic" nature of climbing falls and I think that given the rate these things occur at that they are essentially static, for the purpose of material response, etc...
so I wouldn't think that a fall load is so different from a static load, especially in the sport-climbing application....
we all know (I think) that the "stiffer" the anchor system (including slings, ropes, harnesses, bodies, belay devices, etc.) the higher the forces, but aside from that there is nothing special about how that force is generated... true "shock" behavior only occurs when the forces change over a time short compared to the distance over which they are applied divided by the speed-of-sound in that material... and for climbing that never happens.
by the way, that sort of "thought experiment" helps you narrow your investigation and guide your experiments to those that are essential, and in the end helps to correctly generalize, and more importantly, state the limitations of those generalizations.
otherwise, you are just testing over all the possible situations, and interpolating between the results, which might be fine until you have a situation that does not exist within the domain of your tests
but I agree that the best situation is to confront "theory" with "experiment," the combination of the two is more powerful than either one taken alone
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apogee
climber
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Apr 10, 2011 - 02:09pm PT
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"..a thoughtless Tea Bagger Isn't it redundant to use "thoughtless" and "tea bagger" in the same sentence?"
heh heh
This thread is much more compelling when it stays relatively clear of ad hominems (unusual for ST, I know). Critical observations are useful to the dialogue- don't take them too personally.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 02:14pm PT
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Mighty Hiker,
your first reference corroborates what I have said about hammer taping to determine sound rock for bolting anchor locations.
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Crimpergirl
Sport climber
Boulder, Colorado!
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Apr 10, 2011 - 02:18pm PT
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Thanks Dingus.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 02:22pm PT
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apogee,
I took a course from the Teaching Company -- Argumentation the study of effective reasoning. They contend that mild ad hominems have become acceptable when the fact are clear.
It seems that at the begining of post all the wingnuts come out of the woodwork.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 02:27pm PT
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Ed,
You are right.
In general as long as your real loading situation speed does not exceed the shock wave speed of the material or gu, any slow rate of loading is adequate for the experiment.
Yes we both do thought experiments making use of symmetry and by doing this we decide in what manner to run a real test effectively.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 02:37pm PT
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klk,
esp. since almost none of the sport areas i climb at involve vertical walls or good rock. steep choss if yr lucky. steep mud, often as not.
tilt that baby about forty or fifty degrees.
stop your whining. With the new Makita 18v lithium hammer drill one can easily make a vertical surface for the bolts. Simply put the drill in "hammer only mode" and chisel a flat surface for the anchor face.
Long anchor bolts work better in poor rock than short ones and some times one can achieve good holding power.
ps. if your rap anchor bolting surface is horizontal you haven't finish the climb.
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klk
Trad climber
cali
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Apr 10, 2011 - 02:37pm PT
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I took a course from the Teaching Company -- Argumentation the study of effective reasoning. They contend that mild ad hominems have become acceptable when the fact are clear.
they're obviously a bunch of retards
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 02:51pm PT
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Ed,
to this further I have a saying, applicable to all forms of observation:
All Measurements are Local.
We cannot measure everywhere so we generalize and then decide whether it is applicable.
So I bang the hammer on the concrete and I bang the hammer on a questionable
anchor site, look for cracks, figure out what the composition might be and then decide.
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Mighty Hiker
climber
Vancouver, B.C.
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Apr 10, 2011 - 03:50pm PT
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So we're agreed that a great deal depends on context, and that maybe some climbers could pay a bit more attention to context when placing anchors than they do. Plus we probably agree that anything is better than two 1/4" x 1 1/2" Rawl split shafts for a belay.
This stuff is educational and interesting, and relevant. Pretty clear that there's no one right answer.
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Ken M
Mountain climber
Los Angeles, Ca
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Apr 10, 2011 - 04:10pm PT
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What are the advantages of placing bolts so closely together?
I would go on to say that there may be physical situations in which it is pretty much neccessary to do this.....some canyoneering comes to mind. It is good to know if this is safe, or if it is better to just use one bolt.
There is also another theoretical issue, which has to do with the horizontal distance between bolts. As that distance increases, the force placed on the line/webbing connecting them also increases with the angle at the power point. So you want them closer rather than farther, but this would be an extreme that would give no advantage over, say, 12 inches, for most practical situations.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 04:28pm PT
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Ken M,
there may be very few advantages in placing them close but doing so may be a necessity.
I suspect I would not get bolt pullout even if my bolts were as close together as the bolted on hardware would permit. There are two reason for this. First I place the bolts such that the loading is only from a lateral or shear load. Loading in this way minimizes the region of rock put in tension and is much better than tension force loading. Second, I would tighten the nut to the specified torque and this often will convert a 5000 lb shear force loaded anchor to close to a 10,000 lb anchor due to Coulomb friction forces acting to resist face slippage motion. This scenario is what I would expect for this concrete or any rock that has a higher compressive strength than this.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 04:53pm PT
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Ed and Mighty Hiker,
Here is my take on those spacing tables:
Concrete strength testing is done by adding platens to each end of the concrete cylinder and then this setup is placed in a press and forced together until any cracks are heard or jumps in the load. Almost always the rest of the concrete cylinder is still intact and it often could hold much more load. This test might be seen as partly a measure of how homongenous the mix was.
In most climbing bolt loading situations we see minor cracking at the lower mouth when loaded in shear loading. In concrete testing this minor cracking is what determines the certified limit of that mix. It may be that product catalogs use such a stringent criterion.
Also the data they present may have a safety factor of 4. It is kind of like the "working load" used in chains strength. For chains the ultimate strength may be four times stronger than the quoted working load. Climbing equipment manufactures use ultimate load ratings and not working load ratings. My testing is about ultimate loads and distances that still preserve a chosen ultimate strength criterion. I include no safety factor but would say such and such is the ultimate strength.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 06:42pm PT
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Fort Mental,
good god you are off by just a factor of 5 or 10.
see
http://www.concreteconstruction.net/concrete-articles/maximum-compressive-strength.aspx
http://www.cement.org/basics/concreteproducts_histrength.asp
Standard concrete mixes are around 4000 psi. and are permitted in the building codes. Futhermore the yield of typical tension members in what is call high strength is only 60,000psi.
In my product catalog Hilti products design criteria are specified for 4000psi compressive strength only.
When looking at such manuals we would gain a better understanding if we knew the difference between SUFFICIENT CONDITIONS and NECESSARY CONDITIONS.
These manuals report bolt spacing data that give sufficient conditions to get a safe anchor. But they do not establish whether their spacing is a necessary condition for that same safety goal.
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Auto-X Fil
Mountain climber
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Apr 10, 2011 - 06:55pm PT
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All this talk of strength is ridiculous.
Anchors are redundant because a bolt or the rock might appear good, but not be. Not because a single bolt in good rock might not hold a factor 2 onto the belay.
If it's homogenous, solid rock - put 'em close if you think there's a valid reason.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 07:08pm PT
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Auto-x Fil
If it's homogenous, solid rock - put 'em close if you think there's a valid reason.
I agree! But FYI: Granite though solid rock is random not homogeneous.
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Elcapinyoazz
Social climber
Joshua Tree
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Apr 10, 2011 - 07:18pm PT
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I don't think that's a wild speculation, it is just Newtonian force analysis...
This had me LOLing. Might just be the engineer side of me, but that was funnnnyyy.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 07:37pm PT
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Elcapinyoazz,
yes I have several physicist friends. They tend to reduce problems to some form of one dimensional analysis and then miss the details we have been trained to see. Furthermore todays problems in engineering are often multidimensional and require a more distributed solution than we get when we simplify things too much. That is why engineers design all these finite element computer programs.
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Banquo
Trad climber
Morgan Hill, CA (Mo' Hill)
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Apr 10, 2011 - 08:58pm PT
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In the test picture, the two bolts not being loaded are far enough from the loaded bolt to not have any influence on the strength of the loaded bolt.
Bolt spacing is most critical for loading in tension. The 90 degree (or 45, depending on how you look at it) failure cone actually requires the bolts to be two depths apart for maximum strength. I think Ed said one. The angle of the cone can be more or less depending on the structure of the material. Concrete is usually 45 degrees because it is usually isotropic.
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.
Load duration in climbing falls shouldn't be a factor. In some materials such as composites, polymers and wood, load duration very well could be a factor.
Tension failure modes:
1 metal fails in tension
2 cone pulls out
3 the wedge doesn't hold and the whole bolt pulls out.
Shear failure modes:
1 Metal shears near the surface(some crushing and spalling usually occurs on the side in the direction of the load)
2 the bolt rotates and prys a piece out on the side away from direction of load
3 The side in the direction of load spalls the bolt bends over and fails in bending & tension.
I put a couple papers for Ed here:
http://www.engr.sjsu.edu/dmerrick/misc/
Image only, no text in an effort to avoid Google bots. I'll take these down soon.
Testing is good, it helps people understand how things work and sometimes reveal something nobody thought of. Keep breaking stuff.
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nature
climber
Kovalum Kerala India
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Apr 10, 2011 - 09:27pm PT
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good stuff.
I'd like to see a force applied that is not 0 degrees to the surface of the cement (as someone else pointed out).
I (as well) would also like to see a load on all three bolts at once.
oh... and do it in Sedona sandstone please ;-)
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couchmaster
climber
pdx
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Apr 10, 2011 - 09:43pm PT
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Good stuff, as climbers, we see too little testing of our assumptions. Ed Leeper use to do this kind of thing all the time, and the results were interesting and informative. As far as the Mfg recommended spacing goes, you need to consider that typically these are used in engineered buildings whereing all the facts are known. They are suggesting that although a single 3/8" will get you 5,000 lbs, do not believe that 2 3/8 will get you 10,000 lbs. There is a reduction based on the factors they discuss.
From our viewpoint, as there is even less testing and checking in climbing applications, we have it on our shoulders to be extra careful. Given that and in reference, back in the day it was common to use 1/4" diameter studs that were 1-1/2" deep. The business end of a compression stud that length was even less. So given that the 3/8 are so much stronger, I don't sweat this stuff. 6 inches, 8 inches...as long as there are no fracture planes should be good to go.
Thanks again for the tests !
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 10:01pm PT
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Hey Banquo and couchmaster,
it is good to from those who have studies these scenarios. I am doing some more test and will soon have a load cell and bridge.
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Paul Martzen
Trad climber
Fresno
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Apr 10, 2011 - 10:03pm PT
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hey Dingus Mcgee, Thanks for posting up these tests and the other thread stuff as well. Very interesting reading for me as I love seeing different ways that people actually test stuff.
Overall your results do not surprise me, but several items you mention are things that I definitely had not though about, such as the increase in sheer strength with properly torqued bolts, and the particular opening shape of the open cold shuts. Very interesting. Always inspiring to me to see such experiments and low tech ways of conducting them.
Paul
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 10:10pm PT
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Nature,
It would be very unlikely in a climbing situation to load 5000 lbs on three anchors simultaneously. I try to figure out a possible/likely failure path and then decide how to best test it.
There are big rocks in the country that I could set up an axial pull collinear to the bolt z-axis using their vertical faces. In general I try to avoid totally or avoid adding much tension loading because rocks are much weaker in tension. This strategy keeps my choices simple.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 10:16pm PT
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Hey Paul Martzen,
thanks for the compliments. You have inspired me enough to make a posting of how I make Ramhorns. In this chatter we all end up make our references richer in intuition and realize some unforseen limitation of our thoughts.
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Dingus McGee
Social climber
Laramie
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Topic Author's Reply - Apr 10, 2011 - 10:38pm PT
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hey Banquo,
right on!! for Expansion Inserts from 6-15 of the text Anchorage,"Therefore it is advisable to limit their use to connections with more shear than tension applied to them."
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nature
climber
Kovalum Kerala India
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Apr 10, 2011 - 10:44pm PT
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I agree that loading three at one is unlikely. Thats not my interest.
I'm wondering what scenario it takes to get a cone fracture. Attempting that might quiet some of your critics.
Thinking outside the box in a way.
It seems to me that to get a cone fracture it's more likely if all three holes are loaded.
Know what I'm getting at here?
By the way... That Ed is engaging this thread the way he is is a positive sign for validity in my opinion. Hes a smart monkey.
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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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