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reedcrr
Apr 5, 2004, 9:27 AM
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Those damn euro's have confussed our american minds again! In repeated threads I have read on RC.com there are many post's regarding gear failure thresholds and testing parameters and so on. I am not convinced that most climbers understand what vendors are talking about when the claim a locking biner has, "a max. "long axis load" of 28Kn before possible failure".
So I will try and explain it in layman's terms to those who are interested...if your not continue on to another thread! Stick with me this is easy to understand once you know the math!
Possible failure of any piece of equipment has many complex factors but let's deal only with the basics that can be understood quickly.
In our test piece we will be simulating a test on a Petzl, Williams Locking carabiner. ( Legal crap...We are not actually going to test this item and the numbers given are for education purposes only, refer to your owners manual that came with your biner for actual factors!) We will be using an 11mm Dynamic rope and a 165 lb. lead climber with a belayer that weighs 165lbs. and is not anchored and does not know how to do a running belay. Whew what a mouthful! :D
First we need to convert english to metric...so
1 lb. = 0.45 kilograms so... 165 lbs. = 74.8 Kg (in mass).
We will then have our climber take a 5 meter fall while attempting to clip. (He missied the clip and came off, poor guy!! :cry: ) This is a common fall distance in sport and trad climbing.
1 meter = 3.28 Ft
5 meters = 16.4 Ft or roughly 8.25 ft above the last piece of protection when he came off the rock.
But we said he was going for the clip when he came off so lets add 1.5 meters of slack in the line (from the belayer) so the total drop distance from start to finish is now 21 Feet, 8.25 Feet above the bolt and 12.75 ft below the bolt. Let's hope this climber is up high enough to fall that far safely! :shock:
The Williams biner has three measurements associated with it for load testing (so does every other biner made) and these are:
Load across the long axis : 28 Kn (this is the normal load on the biner if used correctly)
Gate open : 8 Kn (This is forgetting to close the screwgate and the gate comes open under the load of the falling climber)
Short axis : 7 Kn (This is cross-loading, common load failure of an incorrect belay setup or a possible failure due to clipping the lead climber in rather then tying in. Biner tends to want to "walk" while climbing and may get stuck in this cross-loaded position.
Now we need to figure out the applied force of our falling climber when he comes to the bottom of the fall.
1 Kn = 224.8 Lbs./force (this is a force measurement, not weight)
Again.. the Williams Locking carabiner possible failure limits:
28 Kn = 6295 Lbs./force (Applied force in pounds before possible failure)
8 Kn = 1799 Lbs./force (Applied force before possible failure)
7 Kn = 1574 Lbs./force (Applied force before possible failure)
Big difference! With the gate locked and closed and oriented in the correct position the biner is 4 times stronger then the same biner in a cross-loaded situation. So what does that mean to our climber in the above test? Can we even get close to 1574 lbs./force with our 165 lb. climber? Sounds like a lot of force...but just think if you jump off of a two foot chair on to a beer can you are applying about 2 Kn of applied force on to the top of that can with your foot! Or roughly 450 lbs./force...(Again, assuming you weigh in at 165 lbs.) If your going to try the beer can test don't do it barefoot!
Well our climber coming to a stop after falling 21 Feet is going to generate around 1230 Dekanewtons (DaN) of force.
1 DaN = 1.01 Kilograms/force or 2.25 lbs/force
1230 DaN = 2765 Lbs./force (Or 12.29 Kn!)
This means that in this senario this 165 Lb. climber, falling 21 Feet (again remember 8.25 ft. above the protection to 12.25 ft. below the protection) is placing 12.29 Kn of force on the belayers locking carabiner... or if the leader is clipped in then 12.29 Kn on their own locking carabiner.
Under normal circumstance with the load going along the long axis of the locking carabiner the belay would hold and the climber would be safe, but if the biner gate is open or the biner is cross-loaded the possibility that the biner will fail is fairly high and a severe risk is being taken.
The biner is normally the weakest link in most climbing setups because most trad protection properly placed will hold 28 - 30+ Kn. and a 3/8 in. x 4in. Stainless rawl bolt properly placed will also hold around 30 Kn before shearing under load. (Depending on the PSI of the rock)
I know this was a long post but hopefully it is informative as to what those numbers stamped on the side of equipment really means in a way we can all understand it. Take it seriously and do not forget to lock the biner and do not put the biner in a "walking" situation where it can get caught and cross-loaded!
Have fun and climb hard!
*edit for typo*
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wvredline
Apr 5, 2004, 12:16 PM
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You lost me when you got to dekanewtons. I get 165 pounds * 21 feet * 4.45 Newtons per pound foot = 15.4 kNewtons. What am I missing?
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geezergecko
Apr 5, 2004, 1:12 PM
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1 deca Newton = 10 Newtons
1 kilo Newton = 1000 Newtons
Therefore 1 kN = 100 daN
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icekubes7
Apr 5, 2004, 1:28 PM
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Thanks man, very informative. What about if you take a whipper on just a normal non-locking quickdraw carabiner? Would it possibly come open during a fall, and therefore severely weaken it?
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quickclips
Apr 5, 2004, 1:35 PM
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Thats the force applied to the belayers biner, but the draw is a different story. It has the force from climber to the biner and from the biner to the belayer, so it is (if everything is aligned) twice that load.
Very nice explination.
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lqdslvr
Apr 5, 2004, 1:43 PM
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Couple of follow-up questions. I didn't see the dynamic rope enter into the calculations. Perhaps that's factored into the ultimate number of 12.3 Kn, but it wasn't apparent. Also, isn't a crucial factor in making this caculation how much rope is out? This same 21 foot fall is going to be much different with 30' of rope out than with 100'. Finally, I also always understood that the friction and pulley effect with the biner on the piece catching the load would create about 1/3 less force on the belayer than on the leader. In other words, the leader may take 12.3 Kn, but the belayer will only feel 8.2 (and these two numbers must be added to calculate theforce applied to the biner onthe piece catching the fall, e.g, the top draw). I apologize if these are stupid questions; I'm just trying to understand the theory.
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scottd
Apr 5, 2004, 1:53 PM
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I didn't see anywhere in the post, the length of rope from the belayer to the climber. This will greatly affect the force applied to the biner... Or is the total distance 21 feet?
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oldsalt
Apr 5, 2004, 2:05 PM
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I understood that 12 kn is likely a fatal strain on the human body. As noted in a previous post, you could be describing the effects of a static rope. Dynamic rope stretch makes all the difference.
Good intent in the post, clarification needed.
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aklimerguy
Apr 5, 2004, 2:21 PM
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Reedcrr said :
"The biner is normally the weakest link in most climbing setups because most trad protection properly placed will hold 28 - 30+ Kn. and a 3/8 in. x 4in. Stainless rawl bolt properly placed will also hold around 30 Kn before shearing under load. "
Trad pieces range between 8 and 15 kN and your rope at the knot, 12 to 14 kN. Which would make the biner the strongest link, except maybe if you're clipped onto a bolt in granite rock. Or if the biner gate opens at the moment of the fall. Hail to wiregates!
You also forgot to talk about the fall factor (length of the fall/length of the rope between leader and belayer) which is in my point of view, the most important point to consider.
You did however do a great job explaining what a kiloNewton was, which I think was your main objective.
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ben87
Apr 5, 2004, 2:33 PM
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Interesting. I think the basic calculations of force above are all correct -- the effect of a dynamic rope is very important, obviously. I'd also like to see a close examination of the forces on the top piece, especially the carabiner -- which in many leading situations is a non-locking biner, even a wiregate. it seems to me that this is the point in the system where the most force is generated....?
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aklimerguy
Apr 5, 2004, 2:37 PM
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Ben wrote :
"I'd also like to see a close examination of the forces on the top piece, especially the carabiner -- which in many leading situations is a non-locking biner, even a wiregate. it seems to me that this is the point in the system where the most force is generated....?"
I agree, totally!
Does someone out there know of some "field" tests which would of been conducted?
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rockprodigy
Apr 5, 2004, 3:18 PM
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Just goes to show that anyone can post anything they want on the inernet.
Whether it's true or not!
I don't have time to correct this entire post, but I would like to mention that a pound is not a measure of mass, it is a measure of force. A "slug" is a measure of mass.
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quickclips
Apr 5, 2004, 6:10 PM
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I haven't checked the numbers, but I think these calcs didn't take in to consideration as most people have pointed out the dynamic properties of the rope. Being that a rope stretches say 7%, it increased the total distance the force is being applied for, thereby lowering acceleration and reducing the force. So how much rope that is out is a huge factor to the fall.
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fargoan
Apr 5, 2004, 6:24 PM
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In reply to: Ben wrote : "I'd also like to see a close examination of the forces on the top piece, especially the carabiner -- which in many leading situations is a non-locking biner, even a wiregate. it seems to me that this is the point in the system where the most force is generated....?" I agree, totally! Does someone out there know of some "field" tests which would of been conducted?
hey guys, good timing! check out last month's rock & ice (with the taquitz photo on the cover). they are doing a 3-issue series on fall forces using actual falls to get some "field data."
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robmcc
Apr 5, 2004, 6:29 PM
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Jeebus. That's not a good post at all, it's total misinformation and misunderstanding. That's not describing the impact force on a static rope, dynamic rope, or anything at all. It's just completely wrong. You simply cannot determine the force generated in the fall without taking into account the deceleration time, which is absolutely ignored in the post.
In reply to: 1 Kn = 224.8 Lbs./force (this is a force measurement, not weight)
What is lbs/force, exactly?!?
In reply to: Well our climber coming to a stop after falling 21 Feet is going to generate around 1230 Dekanewtons (DaN) of force.
Explain this, please. You have no idea how much force will be required to arrest the climber, you only know how much kinetic energy he possesses.
In reply to: 1230 DaN = 2765 Lbs./force (Or 12.29 Kn!)
It should be a warning sign to you that your calculations are coming up with numbers comparable to or greater than those generated in UIAA 1.8whatever fall factor tests, and your FF is apparently less than 1.
In reply to: The biner is normally the weakest link in most climbing setups because most trad protection properly placed will hold 28 - 30+ Kn. and a 3/8 in. x 4in. Stainless rawl bolt properly placed will also hold around 30 Kn before shearing under load. (Depending on the PSI of the rock)
Source, please? I don't think I own any pro rated to 30Kn. Harnesses, for that matter, are typically rated to 15 or so. I'm sure as hell not rated for 30Kn. I don't even think my hexes are rated to 30kn.
In reply to: I know this was a long post but hopefully it is informative...
Nope, quite misinformative, in fact. Thou shalt understand physics before trying to explan it to others.
Rob
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curt
Apr 5, 2004, 7:14 PM
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robmcc already pointed out a few good points. In addition to robmcc's comments, reedcrr failed to point out that the maximum force felt by the climber will be equal to the peak tension in the rope, during the time that the climber's fall is being arrested. The highest force on the top piece will be twice this figure, minus friction. The greatest negative acceleration experienced by the falling climber is also inversely proportional to the distance over which the falling climber is brought to a stop. This is why knowing something about the fall factor and rope elasticity is required to properly calculate the actual force experienced. rgold has posted elsewhere how to calculate this.
Curt
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drunkencabanaboy
Apr 5, 2004, 7:26 PM
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ROFL OMG - this thread is a cluster... a moderator should just delete it ROFL... its really pointless.
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billcoe_
Apr 5, 2004, 7:37 PM
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Well, I was going to thank him for his efforts to share with us. Awwww, I'm gong to do it anyway. Point is, you can break a cross-loaded or open biner with a leader fall. The pull on the belayer should be less than on the lead biner due to the friction and runig through the lead biner should it not?
Thanks anyway, not that I understand the math:
Bill
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andypro
Apr 5, 2004, 8:31 PM
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In reply to: The highest force on the top piece will be twice this figure, minus friction.
According to testing done by Petzl (I read it in a two page blurb kinda thing in climbing magazine a long time ago...I could porbably dig through my old ones and find it to be sure if anyones interested) Says that friction is responsible for up to 40% loss in the actual force on the topmost piece. So instead of 200% your lookin at more like 160% or so. They also went on to describe the same effects with a static rope, and then a via feratta setup. I dont remember those numbers though, I do remember that the via feratta one was rediculously high and almost certainly lethal. :shock:
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robmcc
Apr 5, 2004, 9:00 PM
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In reply to: You lost me when you got to dekanewtons. I get 165 pounds * 21 feet * 4.45 Newtons per pound foot = 15.4 kNewtons.
It might be worth saying again that foot pounds is a measure of energy while newtons is a measure of force. You can't convert one to the other any more than you can convert pounds to seconds. They measure different things.
Rob
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reedcrr
Apr 5, 2004, 10:23 PM
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I quoted:
"The biner is normally the weakest link in most climbing setups because most trad protection properly placed will hold 28 - 30+ Kn. and a 3/8 in. x 4in. Stainless rawl bolt properly placed will also hold around 30 Kn before shearing under load. (Depending on the PSI of the rock)"
I retract that statement, most of you spotted this and were correct in the fact that most pro will not hold that much, my mistake in not checking what I was writing. And the calc on the bolt was for a 1/2 x 4 bolt. A 3/8 X 4 bolt will shear at 4500 PSI not 6900 PSI...Sorry for this incorrect information. I did however go over the math used in the calc and it is correct.
As far as a pound not being a measurement of mass? Come on...
And to the question what is Lbf. or pound-force it is this:
It is a unit of force equal to the mass of 1 pound with an acceceration of free fall. (Or 32 ft/sec/sec) Unrestrained mass falling with gravity pulling.
I doubt very seriously that any of you are going to figure out fall factors before tying in and climbing. Also I doubt that before coming off the wall you are going to run calculations on how many Kn you are going to exert on the equipment you have. That is not the point of this thread...
In my first post I ommitted all of the calculations that would send most people in to tailspins, such as the dynamic elongation of the rope and the calculation getting to the final number of 12.29 Kn. Omitted on purpose... Yes a static rope will apply more energy into the equation and a belayer jumping at the right time colud lessen the impact by absorbing energy...so many factors to considered... so for the point of this thread I stuck with a basic pulley system and known forces applied within that system.
As a climber you must understand that there are many factors relating to the possible failure of your equipment, such as weight, force, heat, acceleration and deacceleration and so on and the main reason they print that warning on the side of most equipment is to give you an indication as to what that peice can take before possible failure.
In my post I used a 165 lb. person with a common fall from 8.25 feet above the last piece of protection and the final fall of 21 feet, again fairly common. With this simple example it shows that an average person taking an average fall is applying enough force on a biner to possibly cause serious failure if the screwgate is not locked or the biner has been cross-loaded, simple as that.
If you want to contest the applied physics PM and we will have fun...but the calcs used in my first post are close enough not to warrent a retraction on my part...except the paragraph that I have already retracted above.
So to all of my naysayers out there... pick it apart. The main point was to explain what a Kn is and I think I have done so...
By the way foot-pound is a measurement against gravity and pound-force is a measurement with gravity...just a note...
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jt512
Apr 5, 2004, 10:58 PM
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In reply to: I quoted: "The biner is normally the weakest link in most climbing setups because most trad protection properly placed will hold 28 - 30+ Kn. and a 3/8 in. x 4in. Stainless rawl bolt properly placed will also hold around 30 Kn before shearing under load. (Depending on the PSI of the rock)" I retract that statement, most of you spotted this and were correct...
Your first post was such a mess, I didn't know where to start correcting it. Fortunately for me, a few other knowledgeable people posted up.
In reply to: As far as a pound not being a measurement of mass? Come on...
The pound is both a unit of mass and a unit of force, though the latter is the more common usage.
In reply to: I doubt very seriously that any of you are going to figure out fall factors before tying in and climbing.
You damn well better understand the basic principle behind fall factors before you tie in. If you don't you're a double fatality waiting to happen.
In reply to: Also I doubt that before coming off the wall you are going to run calculations on how many Kn you are going to exert on the equipment you have. That is not the point of this thread...
What the point of your first post was was not clear. You stated that it was about understanding what a kilonewton is. I can explain what kN is in one sentence: 1 kN is equal to 225 pounds of force. What the rest of your post had to do with what a kilonewton is, I have no idea.
In reply to: In my first post I ommitted all of the calculations that would send most people in to tailspins, such as the dynamic elongation of the rope and the calculation getting to the final number of 12.29 Kn.
You should have realized that your result was too high, and rechecked your calculations. You did something wrong!
In reply to: The main point was to explain what a Kn is and I think I have done so...
1 kN = 225 lb.
So did I, using half a line.
-Jay
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trenchdigger
Apr 5, 2004, 11:09 PM
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In reply to: By the way foot-pound is a measurement against gravity and pound-force is a measurement with gravity...just a note...
Foot-Pound is a unit or torque in the english system.
The Pound (or Pound-Force if you like) is a measure of force. Toward gravity, against gravity, in a weightless environ - it doesn't matter. A Pound is a unit of force, period.
I appreciate your point, but I beg to differ on your application of pyhsics. I'm not a professor though and don't have the time or inclination to try to explain.
Relating kilonewtons and pounds is simple since both are units of force.
1 kilonewton = 225 pounds.
Nuf said.
The force exerted by a fall on a dynamic rope is complex and can be roughly calculated by a formula you should be able to find by sifting through posts on this site about that subject. However it's hardly and exact science. See the attached link for more info about pounds, kilonewtons, and gear strength.
http://home.vicnet.net.au/...%205%20Equipment.pdf
~Adam~
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jason1
Apr 5, 2004, 11:12 PM
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Force(N)= Mass(Kg)xAcceleration(M/s2) or F=ma
N=kg(m/s2)
kilo- prefix meaing 1000
acceleration of gravity=9.81 m/s2
Impulse= force/time (N/s) impulse is a force applied over a time... to soften a fall you add more time in dynamics to reduce the impulse... or a large force applied over a long time can be just as hard as a small force applied over short time...
i believe the slug is the english unit of mass
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jt512
Apr 5, 2004, 11:23 PM
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In reply to: In reply to: By the way foot-pound is a measurement against gravity and pound-force is a measurement with gravity...just a note... Huh? Foot-Pound is a unit or torque in the english system.
The foot-pound is commonly confused with foot-mouth-pound, which measures the amount of force required to remove one's foot from one's mouth, a high figure in reedcrr's case, apparently.
-Jay
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