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alpnclmbr1
May 31, 2004, 11:48 PM
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In reply to: In reply to: In reply to: In reply to: The time spans are irrevelant outside of theory... Your physics is fine. (I guess, I didn't check.) Your conclusion was absolutely incorrect. Your statement, quoted above, is wrong and, yes, dangerous to anyone who doesn't know any better. Peroxide is right and you are way wrong. Ted is right--so there. HaHa. Curt
I think and you seem to have agreed, that in the practical sense, there is nothing you can do about this factor. That seems to be a reasonable definition of "irrelevent outside of theory."
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curt
Jun 1, 2004, 12:12 AM
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In reply to: In reply to: In reply to: In reply to: In reply to: The time spans are irrevelant outside of theory... Your physics is fine. (I guess, I didn't check.) Your conclusion was absolutely incorrect. Your statement, quoted above, is wrong and, yes, dangerous to anyone who doesn't know any better. Peroxide is right and you are way wrong. Ted is right--so there. HaHa. Curt I think and you seem to have agreed, that in the practical sense, there is nothing you can do about this factor. That seems to be a reasonable definition of "irrelevent outside of theory."
When you are climbing, there is nothing you can do to mitigate this factor--as far as I know. I think it is important beyond theory though, in the sense that you should keep in mind that not all falls with the same fall factor are equal, with respect to the potential effects on your gear. Many people seem to think that they are.
Curt
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alpnclmbr1
Jun 1, 2004, 12:21 AM
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In reply to: I think it is important beyond theory though, in the sense that you should keep in mind that not all falls with the same fall factor are equal, with respect to the potential effects on your gear. Many people seem to think that they are. Curt
All right, lets turn this hijack in another direction.
I think that the significant (and actually measured) factor in varying forces for a given theoretical fall factor calculation is the intermediate points of friction in the belay chain.
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papounet
Jun 1, 2004, 10:09 AM
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dear
I suggest you read the tests of The Italian Commission for Material and Techniques (CMT) of the Italian Alpine Club (CAI)
http://www.caimateriali.org/Eventi/Torino/computermodel.html
and the documents of the UIAA (hint , check out the archive of 2000/3 magazine http://journal.uiaa.ch/download/20003.pdf
http://www.uiaa.ch/article.aspx?c=185&a=76)
you'll find a summary at
http://www.alpineclubofcanada.ca/services/safety/Notes%20on%20Belaying.doc.
Several points to note:
1. the notion of bomber is not scientific
many reports describe instances of gear that was though bomber and failed, as many describe manky gear that held.
"bomber" is a qualifier that is totally subjective
2. the actual force on a piece of protection is influenced by many variables, such as the type of belay, the proficiency of the belayer, the number of biners or the zig-zag of the rope,...
=> there could be so much friction in the system that the is a braking effect which does not happen at the uppermost piece
=> The actual fall factor is not a true measure of the forces involved, if there is the friction in the system.
I'll let you enjoy the mathematical model developped by the CMT
http://www.caimateriali.org/...puter_model/img5.jpg
http://www.caimateriali.org/...puter_model/img8.jpg
3. unless I am mistaken , the resistance of a piece of gear is not its holding power. A tiny cam may "friction" enough with the rock to "in theory" hold the force, but the small stem will break. A tiny nut may hold just to see the tiny cable break (check manufacturer site for the specs of the cable).
4. gear with low number such as 2kn for micro-nuts were never intended for free climbing, but as progression point for aid. A stopper guaranteed at 8kn may not be enough "in theory", but it may well be enough.
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tedc
Jun 1, 2004, 6:32 PM
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In reply to: Tedc: based on your IC scenario the only conclusion that I can come to is that you are advising running it out near the ground and sewing it up as you get further up the route. wtf
Based on your demonstrated lack of ability to reason logically, I don't find it hard to believe that you could draw such a conclusion from my scenario. Sorry. To anyone else who is having the same difficulty as alpnclmbr1 let me just state simply that the above conclusion is incorrect.
It would be correct to conclude,however,that while a placement may hold a 5' FF .5 fall (low on a pitch (obviously :wink: )). That same placement may NOT hold a 20' FF .5 fall higher in the pitch. This is the essence of my "IC scenario"; and while it is not entirely the essence of my argument, it clearly demonstrates the influence of duration of force in a common climbing scenario.
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tedc
Jun 1, 2004, 6:34 PM
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alpnclmbr1 is right :shock: . There is nothing we can do to change the physics involved with a particular fall. His suggestion then is that is must be irrelevant. There is nothing we can do to change gravity either. Does that make it irrelevant. NO, If fact it is the things that we cannot change that we must understand so that we can design a protection system that actually protects us against such "givens". If you don't understand it or you consider it irrelevant than you are at it's mercy.
In reply to: All right, lets turn this hijack in another direction.
Translation: Sound the retreat.
It would be much more honorable (and informative to the rc.com population) if you would just say. "I was wrong. It is improtant to consider the extra energy (duration of force) in a longer fall."
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bigga
Jun 1, 2004, 6:53 PM
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Methinks you guys all agree with each other and just want the other to see your point. Your difference of opinion here is so subtle this could go on for ever...
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madmax
Jun 1, 2004, 8:19 PM
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This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. (3) Pulling a piece is bad.
Bottom line is that running it out is the culprit when it comes to generating enough kinetic energy to pull a piece, regardless of the fall factor?
Seems like something most trad climbers intuitively know, but perhaps can't articulate.
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alpnclmbr1
Jun 1, 2004, 8:34 PM
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In reply to: In reply to: All right, lets turn this hijack in another direction. Translation: Sound the retreat.
Actually the translation was: lets not try to embarrass Ted to much.
In reply to: It would be much more honorable (and informative to the rc.com population) if you would just say. "I was wrong. It is improtant to consider the extra energy (duration of force) in a longer fall."
Which is more honorable? Being open to new ideas and rational discussion, or being so stuck with being right that you bury your head in the sand?
Duration is effectively a meaningless concept because there are no steps that you can take that will affect it in any way.
For the last time, technically, Peroxide was right and you were wrong and if you do not believe me, ask Curt.
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alpnclmbr1
Jun 1, 2004, 8:37 PM
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In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull.
In most instances, this is completely wrong. Thanks ted.
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madmax
Jun 1, 2004, 8:41 PM
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In reply to: In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. In most instances, this is completely wrong. Thanks ted.
Okay, alpnclimbr1, and why...?
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bigga
Jun 1, 2004, 9:08 PM
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I may have missed some points in your discussion over there so my input may be way off...
If you guys are discussing the pros and cons of the length of time of impact then I'll add my two cents. correct me if I'm wrong.
A longer period of impact force would put the pro under strain for a longer period of time But... As the saying goes, its not the fall that kills you...its the sudden stop at the end that does it. The amount of force felt by any body arrested in its movement is entirely dependant on the amount of time it decelorates from its current velocity to zero. Force (felt when the rope arrests your fall) = Mass * Acceloration and acceloration is equal to the change in velocity over time (from the moment the rope began to slow you down till the moment you stopped) (this is just an average of force since deceloration is not constant). i.e the shorter the period of time you decelorate the larger the force you (and all your gear) feel. Even on a molecular level, an atom hitting a train going the other way would go through a slowing down period even before it made contact, but if it wouldn't and the deceloration period would be zero the force felt (by the train or the atom, you pick) would be infinite and so a fly could be able to break the train. ( Just an anology to show ho much period of impact influences the force felt)
So while a longer sustained force puts pressure on your gear for a longer period of time, wouldn't that be prefferable if it reduced the maximum force a piece felt, assumung a placed piece can hold up to a certain amount of force?
(I have a feeling I'm saying stuff you guys already know, if so, apologies)
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alpnclmbr1
Jun 1, 2004, 9:32 PM
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In reply to: In reply to: In reply to: This has been one of the better discussions I've read at rc.com. :D For us who are not as scientifically savvy as others here, let me see if I have drawn some of the right conclusions. (1) Running it out increases the duration of the force. (2) The duration of the force increases the likelyhood a piece will pull. In most instances, this is completely wrong. Thanks ted. Okay, alpnclimbr1, and why...?
Bigga pretty much covered it.
As far as (1) running it out increases the amount of energy in a fall. The main variable in the duration of that impact force is the elasticity of your rope. The main point is that duration and energy are not interchangable terms.
As far as (2) In most cases increasing the duration of an impact force is equivalent to lowering the force felt by a given piece of pro or anchor. This is why you use a dynamic rope instead of a static one. This is also how a dynamic belay works.
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vicum
Jun 1, 2004, 9:51 PM
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May I try to summarize?
Suppose in situation A, 10kn acts down on a piece for .001sec. In situation B, 10kn acts down on a piece for .01 sec.
Curt and Tedc think that situation has B greater chance for the piece to pull than situation A.
Alpnclmbr thinks each should hold equally well.
Is that it?
Can any of you give a good qualitative explanation WHY either conclusion should be true? Personally, I cannot see why the force acting for a longer time should affect wheather the piece pulls, unless we are talking about the mere probability of random failure.
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alpnclmbr1
Jun 1, 2004, 10:25 PM
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In reply to: May I try to summarize? Suppose in situation A, 10kn acts down on a piece for .001sec. In situation B, 10kn acts down on a piece for .01 sec. Curt and Tedc think that situation has B greater chance for the piece to pull than situation A.
This is a fact.
Read the thread because you are not even close.
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paulraphael
Jun 1, 2004, 10:28 PM
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There's a whole lot of chest thumping going on here over nothing more than conjecture. If you can't produce some EVIDENCE that shows that duration of an equal force matters (or doesn't matter) then you shouldn't be shouting at each other--you should be asking questions, nicely.
My observations:
1) I have never encountered test results that correlate load duration with likelyhood of placement failure, so I don't know the answer.
2) My training in physics leads me to believe that load duration would not be a factor most of the time (or if it were a factor, it would be a minor one compared with the others)--but again, I don't know the answer with certainty.
3) The tests performed by the industry ignore the question, because they are static. By slowly pull testing pieces, they subject them to high forces for much longer durations than any fall.
4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here. I have not seen static tests or drop tests performed on actual rock placements. Rock is so variable that scientifically useful results would be VERY hard to produce. They still might be interesting, though.
Until we see some real evidence, there's no need to be screaming at each other about assumptions and guesses. Life is too short. Climb something.
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jt512
Jun 1, 2004, 10:45 PM
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My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this:
In reply to: 4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here.
Then the light bulb (dim as it may be) went off: Failure is not instantaneous. This is especially true (I would think) for the rock. Subjecting the rock to a given force can cause it to start to fail, but if the duration of the force is short enough, it may not fail completely.
Hopefully, I didn't just state something completely obvious and banal.
-Jay
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curt
Jun 1, 2004, 11:15 PM
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Jay,
I was also trying to make that same point a few pages back.
In reply to: I can think of other failures, besides Ted's example of a cam placement in sandstone that would be real concerns. For example, the bending of a small camming device axle or deformation of small aluminum cams would certainly be more likely by applying a high force for a longer duration of time, rather than over a very brief period of time.
Curt
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tedc
Jun 1, 2004, 11:31 PM
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Since most of the people replying have obviously not read the whole thread and thus not understanding what is being "discussed".
Here is my first comment; to which peroxide replied "bunch of physics....then... time (duration) is irrelevant." then alpnclmbr1 jumped in and agreed with peroxide.
In reply to: In reply to: peroxide, etc... thanks for all the info. however... i'm still having trouble understanding how a 4 foot factor 2 fall can generate the same force as a 50 foot factor 2 fall. Kevin Your confusion is understandable. And you hit upon the key to your puzzlement with the word time. While the FF does essentially determine the max force felt by the system, a longer fall with an equal FF will apply force to the system for a longer time than a shorter fall. For a given FF, the forces will max out (at about the same value) as the climber comes to a stop at the bottom of the rope stretch but the whole time the rope is stretching the force will be building and the rope stretches for a longer period in a longer fall. It an ideal case this time is not to important because if a cam will hold 10KN for .001 sec it should hold 10KN for .1 sec right? Maybe? Other issues like how far does the belayer get pulled up are MUCH more dependant on the amount of time a certain force is applied. How about a FF2 onto a poorly equalized (i.e. cordalette) 3 piece anchor. Forces applied for .001sec. (maybe a 3' FF2) may only be enough to rip the first crappy piece :shock: ; where forces applied for .1sec (maybe a 15' FF2) may be long enough to POP, POP, POP all three crappy pieces. Bye,Bye :cry: So, are all Factor X? falls the same? NO. But then again, didn't Sharma say "Climbing isn't about MATH." :?
I think this is pretty clear, and two EXAMPLES were given. When I still didn't get my point across I gave the third example of the cam sliding in the sandstone crack. This example was not intended to imply that any gear or placement is more likely to fail in a longer "same FF" fall. A piece (and placement) that will hold 10KN will not fail no matter how long you apply 8KN.
The cam in IC example was a special example (given because I have seen it). It shows that if a cam has about 5KN of holding power in the placement and you fall generating about 5KN it will pull if you apply the 5KN force long enough; and, it will slip (cut grooves) and stop if you apply the 5KN for a short enough period of time. I have seen this. I have personally left the grooves in the rock. I have fortunately never had the grooves be longer that the placement was deep.
Some who have not read the entire thread assumed that the discussion was entirely about whether duration has an effect on a piece pulling. That is not entirely true. Duration does have an effect on the performance of some placements.
The first two examples are also relevant and and indicate the relevance of time in more common (for folks who don't climb sandstone cracks) climbing situations.
Anyone ever held a short (5') FF 1.5 off a hanging bealy? Pretty good jolt but not a lot of movement right?
Anyone ever held the same FF1.5 but now 15'. SERIOUS. Belayer gets jerked up several feet. (Possibly loading the anchor in the upwards direction.
If you were belaying off nuts and didn't use a lower piece then I think you might have just found deadly evidence that the difference in duration of force caused by the longer fall IS relevant.
The three piece anchor example is left as an exercise for the reader (My fingers are getting tired and I have to climb tonight.)
Oh. one more thing. Ask mtngeo if duration of force can lead to anchor failure. If he had removed the load after KB #1 or #2 pulled he wouldn't have cratered. Longer timeframe (granted) but I'm sure you all can do the necessary interpolation to apply this to your own anchors and your own falls(loads).
So yes I was yelling; because I gave the evidence and no one read or listened or understood. And I would have given up a long time ago if so many new people weren't interested enough to keep posting. I don't care about convincing a couple people that I'm right, but if lots of folks are reading they deserve to hear the WHOLE story.
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jt512
Jun 1, 2004, 11:33 PM
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In reply to: Now back to the begining... My hole question was... based on this how can a cam rated 8KN or lower be considered a bomber piece. And as most people have told me so far it isn't. Obviously the piece can peform above its specs, and hold a larger force than its intended to, but its not a given that it will. In theory a cam should hold an infinite force, but its axle has a limit (quite a high one) and so does the rock that its placed in. So... wheres the booboo in my reasoning? Something a little more helpfull than "you're lost" would be nice.
Not every fall generates the maximum impact force. Most falls generate a small fraction of that. Climbers don't rely on a single small cam when the potential impact force would exceed the strength of the cam in that placement. When the possibility of a factor-2 fall exists, the minimum anchor is three equalized pieces. If the pieces are marginal, then more.
-Jay
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alpnclmbr1
Jun 1, 2004, 11:43 PM
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In reply to: My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this:
Not you to.
If the above were true nobody would use a dynamic belay. Also when placing sketchy gear you would be better off belaying with a grigri instead of an atc.
In reply to: In reply to: 4) However, static pull tests show breaking strengths very much in line with breaking strengths during drop tests. This suggests little significant difference based on duration. However, the nature of rock is an important variable that is not taken into account here. Then the light bulb (dim as it may be) went off: Failure is not instantaneous. This is especially true (I would think) for the rock. Subjecting the rock to a given force can cause it to start to fail, but if the duration of the force is short enough, it may not fail completely.
Once again there is no way to affect the balance between the duration and the force except by using a higher impact rope.
Are you guys seriously suggesting that we start using higher impact force ropes in order to address this issue.
Petition the uiaa, I am sure they would be very interested in addressing this new important issue. This has already been covered and current theory hold that exchanging a longer duration for a lower impact force is the way to go.
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alpnclmbr1
Jun 1, 2004, 11:48 PM
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Rgold your input on this would be helpful.
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jt512
Jun 2, 2004, 12:13 AM
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In reply to: In reply to: My intuition has been telling me that increasing the duration of the force increases the probablility of failure, but I hadn't been able to figure out why until paulraphael posted this: Not you to. If the above were true nobody would use a dynamic belay. Also when placing sketchy gear you would be better off belaying with a grigri instead of an atc.
Hardly. We use a dynamic belay to increase the duration of the force in order to reduce the maximum impact force. Obviously, this is a favorable trade-off. But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure.
-Jay
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alpnclmbr1
Jun 2, 2004, 12:19 AM
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In reply to: But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure.
Is that really a question? Of course it does.
Now what are you going to do with that information?
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curt
Jun 2, 2004, 12:29 AM
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In reply to: In reply to: But the question at issue is: for a given maximum impact force (ie, fall factor), does the duration of force (ie, length of fall) increase the probability of failure. Is that really a question? Of course it does. Now what are you going to do with that information?
Hopefully, when evaluating whether a gear placement is adequate or not, you are going to take into account more than just the fall factor alone. That, I think, is the lesson to be learned here.
Curt
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