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Ken
Trad climber
Arroyo Grande
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Topic Author's Original Post - Jul 10, 2012 - 01:35am PT
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An old metallurgist friend of mine (Bill Hoffman) borrowed some hardware from me for testing back in 1987 or so, just ran across a slip of paper with these results:
Approx. tensile strength
* 1/4" Star Drive 1750 lb
* 3/8" Star Drive 3430 lb
* 1/4" Rawl (split shaft, threaded) 6072 lb
This was at a time when many people relied on a line from George Meyers' Yosemite Guide that said Star Drives may be the best bolts.
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ec
climber
ca
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Jul 10, 2012 - 01:38am PT
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Isn't shear strength more applicable for all but overhanging routes?
Just sayin'
 ec
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Loomis
climber
Peklo Vole!
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Jul 10, 2012 - 02:32am PT
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You must be kidding?
Andy Solowe and I did test on these bolts and others in 1979/80
Our values differ greatly from what you represent on this thread.
Do you have access to the technical data from your friend? Depth, batch number and rock applied to, ect...
A new generation of climbers, reading your information, will be ill inspired by the vague information you provide.
ec has a point, where's the shear values?
This must be a troll ;)
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Juan Maderita
Trad climber
"OBcean" San Diego, CA
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Jul 10, 2012 - 05:31am PT
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Ken,
Those test numbers seem inflated if you are describing strength of the installed fastener in tension or "pullout strength." As worded, "tensile strength" those numbers could be accurate for the 1/4" Rawl DriveŽ (split shaft) contraction bolt. Tensile strength is the actual strength of the (steel) material when pulled, before it starts to "neck" and fail. One chart shows a tensile stregth for 1/4" x 20 (coarse thread pitch) of 6192 lbs. Another chart shows min. tensile strength for 1/4" x 20, Grade 2 (heat treated carbon steel) = 2350 lbs.,Grade 5 = 3800 lbs., and Grade 8 = 4750 lbs. I'm just guessing that Rawl Drives are heat treat hardened to somewhere between Grade 2 and Grade 5. (Does anyone know the answer to that one?)
The numbers that climbers (and the fastener/construction industry) are interested in are tension (pullout) and shear strength when installed. Tensile strength is not particularly relevant. I see no reason to post tensile strength numbers. In fact, the confusion could be dangerous if someone were to mistake the term "tensile" strength for "tension" (pullout) strength.
I've heard of Rawl (now Powers) DriveŽ 1/4" contraction bolts testing with shear numbers of up to 2,400 lbs. in granite. Pullout strength is less. Certainly not in the 6,000 lb. range.
For reference, the Powers web site shows specs for the 1/4" DriveŽ as:
2090 lbs. ultimate shear strength and 1760 lbs. ultimate tension, in 6,000 psi concrete. "Mushroom" head, aka: round head, buttonhead. Minimum embedment depth 1-1/8". The threaded "stud" type were short, probably not over 1" embedment with hanger installed.
The ultimate strength numbers in 4,000 psi concrete are the same. 2,000 psi concrete results in lower numbers. That leads me to believe that beyond 4,000 psi, the hardness of the rock is not the issue. It is the bolt failing at 1760 lbs. tension and 2090 lbs. shear.
The longer 2" buttonhead may give slightly higher numbers, but to my knowledge the threaded stud type were not manufactured, or at least never used by climbers, in 1/4" x 2" length.
The bottom line: A new 1/4" Powers DriveŽ bolt, perfectly placed in the best quality hard rock = 2090 lbs. ultimate shear strength and 1760 lbs. ultimate tension.
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steveA
Trad climber
bedford,massachusetts
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Jul 10, 2012 - 07:28am PT
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I taught strength of materials courses for years, and custom built a hydraulic tensile testing machine with a capacity of 70k lbs.
I just want to mention that mild steel has a pretty consistent tensile strength of 60-70K lbs. per square inch.
Doing the math- a 1/4 inch bolt has a cross-sectional area of .0489 sq. inches. Multiplying .0489 X 70K lbs. = approx. 3400 lbs. tensile strength.
I assume that most expansion bolts, are heat treated to some extent, and shear strength, depending on the situation, can result in different measurements.
In my class we used to stretch 1 inch diameter steel bars until failure.
As they neck down, the steel work hardens, and when the specimen finally breaks ( fails), the noise is quite loud. Many students were quite impressed.
After I retired, the teacher who took over, scraped my machine.
He saw no value in it--sad.
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ec
climber
ca
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Jul 15, 2012 - 11:49pm PT
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'Kludge,
Thx, however, I was being the Devil' Advocate...
ec
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Salamanizer
Trad climber
The land of Fruits & Nuts!
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Jul 16, 2012 - 02:42am PT
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The ultimate strength numbers in 4,000 psi concrete are the same. 2,000 psi concrete results in lower numbers. That leads me to believe that beyond 4,000 psi, the hardness of the rock is not the issue. It is the bolt failing at 1760 lbs. tension and 2090 lbs. shear.
From everything I have ever read I think your suspicions are correct.
However, it's been my understanding that Powers "split shaft" bolts are crap, or they seriously understate the actual numbers.
The bolts I use are from ConFast. http://www.confast.com/products/technical-info/split-drive-anchor.aspx
Their numbers are quite a bit higher with 5400lb shear and 2200lb pull-out for 1/4in X 1-1/2in bolts. The numbers remain the same for longer bolts which backs up your theory.
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DanMerrick
Social climber
FKA Banquo from Mo' Hill, CA
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Sep 22, 2018 - 07:47am PT
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Greg Barnes send me some new Star Dryvins to play with about 5 years ago. The video is low quality. The display reads out in kips, kilo-pounds or thousands of pounds.
The load cell calibration is per the load cell manufacturer's data sheet. Back then I was still teaching at SJSU and verified the calibration in one of their universal testing machines.
Note that a #13 BD stopper is rated for 10 kN (2248 lb).
[Click to View YouTube Video]
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BruceHildenbrand
Social climber
Mountain View/Boulder
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Sep 22, 2018 - 09:10am PT
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Dan,
Cool video! Glenn Denny told me that he used to replace the lead at the end of the Star Dryvin with thicker stuff because he felt it increased the pullout strength.
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Ksolem
Trad climber
Monrovia, California
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Sep 22, 2018 - 07:51pm PT
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All I know about the strength of 1/4" bolts is that when I pull one placed in the 80's - that's when anyone ever used them - they come out like a nail comes out of rotten wood. Since no one uses them any more that's all I need to know.
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JimT
climber
Munich
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Sep 23, 2018 - 09:01am PT
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You are putting faith in a flawed concept! The slowness of the extraction in the videos is merely an artefact of the fact the tester is being operated with a hand pump, put it on my tester set at the speed required for certifying bolts and it would rip straight out in seconds. Put it on my drop tester and you wouldn´t see it go!
The question is actually is the work of failure (the amount of energy required to pull the bolt out) which can be derived from the area under the force/time curve greater or lesser than the energy provided by the climber which you obtain the same way. You need to match the energy at any point to the force required/the force imposed but that´s easy enough.
Looking at the forces in the video and the distortion in the hanger I´d describe the holding power as pathetic, no modern bolt would fail in that orientation under over 30kN.
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Steve Grossman
Trad climber
Seattle, WA
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Sep 23, 2018 - 09:20am PT
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Neither of these bolt designs are suitable for catching repeated falls in climbing situations period. Stop using them folks.
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JimT
climber
Munich
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Sep 23, 2018 - 11:10am PT
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Quote Here its wasn't so much the time frame as the number of exertion of said force it took
I cant imagine a fall whose arrest would exert that force more than once on the bolt and it took many applications of that force in those examples
No, it only took repeated applications of force because the hydraulic ram only travels 1 or 2mm at a time, on a normal tester it would be one smooth pull and come out and on a drop test it would fly out faser than you could see.
You are seeing artefacts from the testing method and falsely attributing a bolt characteristic to them.
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DanMerrick
Social climber
FKA Banquo from Mo' Hill, CA
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Sep 23, 2018 - 05:04pm PT
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For the sake of discussion, let's say a 200 lb guy falls 20 feet. The fall generates 200x20=4000 ft-lbs of energy that needs to go someplace. Let's say an anchor requires 4000 lbs (17.8 kN) of force to break and although it is never the case, assume the force is constant over the distance required to break it. Let's conservatively say the distance is 2 inches (5 cm). 4000 lbs over 2 inches is 8000 in-lbs of energy to break the anchor. An actual anchor will likely only absorb a fraction of this energy. 8000 in-lb is only 8000/12=667 ft-lbs or 1/6 the fall energy of 4000 ft-lb.
I doubt that the energy absorbing capacity of any anchor is going to save you if you fall. Plus, even if it doesn't break, it is likely only good for a single use if it is used to absorb energy. The energy of a fall is best absorbed by something that acts as a viscoelastic system. The rope is where the energy goes. Ropes are designed to be good energy absorbers.
Realistically, falls seldom generate the large forces that people think they do. That's why a #6 stopper is often good enough to catch a lead fall. A #6 stopper is rated for 2250 lbs (10 kN).
The fall factor is the best way to estimate the force in the rope. The force on the anchor will be less than but close to twice the rope tension. Phillips, Vogwell and Bramley of Mechanical Engineering Department at the University of Bath in the UK predicted the force in the rope during a fall by looking at the rope as simple spring. They then verified their model by doing some drop tests with a 55kg mass and measuring the rope tension. Their model was conservative because it ignored the viscous behavior of the rope. Their tests were conservative because they ignored the friction loss as the rope passes over the carabiner at the anchor. Also, since they tied the anchor end of the rope off they ignored the influence of belay device slippage and belayer bounce. Their calculated and their measured forces are high.
The chart maximum is about 3.5 kN or about 800 lbs so, for a 55 kg factor 1 fall the force on the anchor will be less than 1600 lbs. 55 kg is a small person of 120 lbs.
I would estimate that my 200 lb (91 kg) guy falling 20 feet (6.1 m) with a fall factor of 1 would generate a force on the lead anchor of less than 2600 lbs. I wouldn't be surprised if he was injured by the 1300 lb or 6.5 G jolt.
Anyway, any climber who is repeatedly taking factor 2, or even factor 1, falls needs to reassess their climbing technique. And, by the way, in my opinion, nobody should be using Star Dryvin's for climbing. If you are out there on lead and you happen across one, goahead and clip it.
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JEleazarian
Trad climber
Fresno CA
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Sep 23, 2018 - 10:32pm PT
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When I started climbing in Pinnacles in the mid 1960's, I took Roper's advice and brought a bolt kit along equipped with 3/8" Star Dyvins. A trip to Pinnacles then yielded a variety of old bolts, and still does if you venture off the beaten path. Not all were bad, but I could remove several with my hands. Most of the bad bolts were 1/4" Rawl drives, often placed in too shallow a hole, but I've never seen one fail because of inadequate tensile strength. The design simply didn't work well in the soft rock.
Interestingly, some of the ancient, 3/8-inch, Stars still seemed pretty solid, so maybe the design wasn't as bad as it seems now. In any case, I'm grateful for changes in the design and material used in modern bolts used for climbing.
John
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