Discussion Topic |
|
This thread has been locked |
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Original Post - Apr 10, 2011 - 11:20am PT
|
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.
|
|
Studly
Trad climber
WA
|
|
|
Apr 10, 2011 - 11:22am PT
|
What route is that on? It looks vaguely familiar...
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 11:52am PT
|
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.
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:05pm PT
|
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.
|
|
Crimpergirl
Sport climber
Boulder, Colorado!
|
|
|
Apr 10, 2011 - 12:25pm PT
|
What are the advantages of placing bolts so closely together?
|
|
Ksolem
Trad climber
Monrovia, California
|
|
|
Apr 10, 2011 - 12:28pm PT
|
So you only loaded the middle bolt?
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:30pm PT
|
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.
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:35pm PT
|
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.
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:38pm PT
|
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?
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:40pm PT
|
locker,
I hear ya. This is actually the neighbors garage slab apron that he is going to replace.
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:42pm PT
|
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?
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:52pm PT
|
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.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Apr 10, 2011 - 12:56pm PT
|
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!
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 12:57pm PT
|
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!
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 01:00pm PT
|
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.
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 01:04pm PT
|
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.
|
|
klk
Trad climber
cali
|
|
|
Apr 10, 2011 - 01:09pm PT
|
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.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Apr 10, 2011 - 01:09pm PT
|
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
|
|
Dingus McGee
Social climber
Laramie
|
|
|
Topic Author's Reply - Apr 10, 2011 - 01:10pm PT
|
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.
|
|
Salamanizer
Trad climber
The land of Fruits & Nuts!
|
|
|
Apr 10, 2011 - 01:10pm PT
|
Garage floor or not, I can't believe you bolted that close to a crack.
Interesting discussion, carry on...
|
|
|
SuperTopo on the Web
|
Let us know!