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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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