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alpnclmbr1
Jun 2, 2004, 12:36 AM
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In reply to: 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
Sounds good to me.
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p_grandbois
Jun 2, 2004, 12:46 AM
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I think in the end Bigga would like to make the product he is making with a rating for the max force for a factor 2 fall, like a lot of pro. I am glad for one that he is doing this large amount of research, and asking questions about the KN's. Climbing may not be about math but gear production is(for a large part) It has to be able to hold up to the math to get certified. He has a great drive, and is taking the neccessary precautions.
Like I said from the start, make it as bomber as the math tells you too, then work your way down for specifics. Don't focus on the naysayers that just want to put their ethics into making gear. Math is needed for this, might as well make it right.
p.s I am majoring in Athletic Management, not math
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alpnclmbr1
Jun 2, 2004, 12:58 AM
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In reply to: 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.
You are offering problems but not any solutions. This is what happens when you offer theories that are "irrevelant outside of theory"
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rtc
Jun 2, 2004, 1:05 AM
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o.k. .........I'll take the pink one. :?
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jt512
Jun 2, 2004, 1:09 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?
I don't know. Not much, I suppose. Maybe it's a reason not to skip a gear placement high on a pitch.
-Jay
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bigga
Jun 2, 2004, 2:22 AM
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Philly, thanks for the good word...
This thread left my original question a few pages ago, though:)
Its been an interesting discussion all the same.
How goes the wires?
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vicum
Jun 2, 2004, 3:55 AM
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In reply to: 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.
Really????? I DID read the thread.
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alpnclmbr1
Jun 2, 2004, 4:17 AM
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In reply to: Really????? I DID read the thread.
oops
Then it is a case of my being unclear. I try.
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hugepedro
Jun 2, 2004, 4:32 AM
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The only thing I've learned from this thread is that I will never buy a piece of gear designed by bigga.
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ic2d
Jun 2, 2004, 5:17 AM
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Bigga,
Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope. By your reasoning, the load felt on the biner is then closer to 25 kN as that force must be applied on both sides of the rope. Methinks this isn't entirely accurate...after all, we're not talking about a statically loaded pully system (is statically even a real word?). Anyway, since the belay end of the rope is not falling, your belayer would have to weigh somewhere in the neighborhood of 2700 pounds (for a split second) to create an equal force on the other end of the rope. The more likely scenario is that the 12 kN force created by a falling climber lasts just long enough to pull the climber upwards (and quite far on a fall like this), without an equal balancing force on the opposite end of the rope, until the fall force is damped out by rope stretch and friction. If the forces were equal on both sides, the belayer wouldn't move...right? Assuming my understanding of what's going on is correct, the belayer side of the rope never pulls more than 1 kN (making a 13 kN total load on the biner) - for your average adult male climber, that is. Now if your belayer decides to bungee jump on his end of the rope while you're falling, then thats an entirely different story.
On a side note, I'm hoping no one else has made this same statement. I suppose its possible that I may have missed it somewhere in the last 8 pages of this thread (although I rarely, if ever, make mistakes).
Where'd everyone go?
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curt
Jun 2, 2004, 6:28 AM
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In reply to: Bigga, Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope.
No it won't. In fact, it will not exceed 9 kN for any rope I know of.
Curt
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alpnclmbr1
Jun 2, 2004, 7:13 AM
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Curt,
The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor.
This can translate to apx. 12kn for a full factor 2.
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curt
Jun 2, 2004, 7:19 AM
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In reply to: Curt, The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor. This can translate to apx. 12kn for a full factor 2.
I prefer to believe this, from another thread.
In reply to: ........... Since climbing ropes develop a maximum tension of 9 kN or less, girth-hitched spectra should be adequate for any protection situation.
Thanks though.
Curt
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beesty511
Jun 2, 2004, 7:26 AM
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In reply to: No it won't. In fact, it will not exceed 9 kN for any rope I know of.
lol. I see you quote that 9kN figure in post after post whether its on the climber, the gear, or the anchor. Is that some sort of gravitational constant you worship? You don't know of any ropes where a climber will feel more than 9kn in a fall? I could provide you links to quite a few. And, that 9kN is the max for every climber for every fall? I guess the climber's weight isn't a factor on planet curt nor the fall factor. Of course, in all the fall factor threads you post to you show your ignorance of that concept too. And, the effective fall factor can be higher than the theoretical fall factor. And....
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curt
Jun 2, 2004, 7:39 AM
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In reply to: In reply to: No it won't. In fact, it will not exceed 9 kN for any rope I know of. lol. I see you quote that 9kN figure in post after post whether its on the climber, the gear, or the anchor. Is that some sort of gravitational constant you worship? You don't know of any ropes where a climber will feel more than 9kn in a fall? I could provide you links to quite a few. And, you aren't aware of any climbers that will feel more than 9kN on your magic rope? I guess the climber's weight isn't a factor on planet curt nor the fall factor. Of course, in all the fall factor threads you post to you show your ignorance of that concept too. And, the effective fall factor can be higher than the theoretical fall factor. And....
Ah, Betsy. How nice of you to chime in to spray inaccuracies once again. I have never claimed the 9kN to be the maximum force felt by the gear--only by the falling climber. And, this is also the figure cited by rgold, as you can clearly see from my post above. Why? Because as rgold states, that is the maximum tension that will be developed in a modern climbing rope. But I am sure you know far more about these things than we do dear Betsy.
Do not pass Go and do not collect $200. Instead, go directly to Jail for being an idiot.
Curt
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papounet
Jun 2, 2004, 10:01 AM
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In reply to: Curt, The range for current ropes on the market is 9.2 kn to 10.5 kn. This is for a uiaa 1.78 Fall factor. This can translate to apx. 12kn for a full factor 2.
How do you "translate it" ?
The 9.2 kn to 10.5 kn is the force felt by the climber for the first fall. subsequent falls inflict progressively more and more force. The rope (in part, because of the 5mn interval between tests) does not recover all of its elasticity.
Please note that the UIAA test measure the force on the first drop. it then only test the rope till failure and reports the maximum number of falls.
I believe it is possible to extrapolate the maximum force inflicted to the dummy for a ff 2.0 either from the modulus of the rope given by the static elongation or from the modulus given by the test at ff1.78.
The issue: we get 2 different values,
Nonetheless, using the second formula, a rope that inflict 10 kn in a ff 1.78 can be predicted to inflict 10.5 kn in ff 2.0
(of course, a rope that has been used inflict harsher falls as demonstrated in various experiments, and then the maximum force could reach 12 kn)
I am here nit picking on this 12 kn value which is often quoted as a "magical golden number".
It has been said that the setup of the UIAA test is actually a bit harsher than the 1.78 factor woul suggest.
Some practitionners such as http://www.usmga.net/resourcesaskarchivedetails.cfm?RecordID=86 say
"The UIAA test is considered more severe than reality because it removes variables like belay devices, belayer's body, friction between the climber and the rock, etc. It is therefore hard to pinpoint exactly how much force will go onto the climber. "
In fact it doesn't take also into acount the deformation of the body of the climber which does absorb energy.
read also
http://www.usmga.net/guidelines/guidelinesropes.htm
this would make me think that in most case, the actual force seen by the climber is much lower than the value reported by the UIAA test
The UIAA tests are applied by several labs. A few years ago, there was some serious isues with the consistency of the measurments, in other wors, some labs were "nicer" than others and gave lower imapct force measures. The UIAA has, I believe, engaged in a re-certification of the labs and has tightened the standards fot the testing process.
RESEARCH at Padova and by rope makers, as well as the statistical evidence that NO well maintained rope has broken in the last 20 years would make me think that in most case, the actual ff seen by the hardware is much lower than the theoritical value
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papounet
Jun 2, 2004, 10:21 AM
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In reply to: Bigga, Seems to me your cam loading estimate is a little high, which seemed to be an important part of your original question. As has been stated, a factor 2 fall should produce about a 12 kN force on the climbers end of the rope. By your reasoning, the load felt on the biner is then closer to 25 kN as that force must be applied on both sides of the rope. .... ... Assuming my understanding of what's going on is correct, the belayer side of the rope never pulls more than 1 kN (making a 13 kN total load on the biner) - ... On a side note, I'm hoping no one else has made this same statement. I suppose its possible that I may have missed it somewhere in the last 8 pages of this thread (although I rarely, if ever, make mistakes). Where'd everyone go?
Missed several points:
1. a fall with ff 2.0 will not generate 12 kn , rather 10 kn with a modern rope in (very) good condition. the 12 kn is the maximum limit stated by the UIAA standard.
2. if you do not have any carabiner acting as a pulley in your system, the anchor onto which you have affixed the belay system will see the total force of the fall 10kn.
3. if you have setup a draw on the anchor, by virtue of the friction on the biner, the force seen by the belayer side is ~= 60%, the force seen by the anchor is ( 100% +60% ) the force felt by the climber = 16 kn
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papounet
Jun 2, 2004, 10:52 AM
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In perfect rock, the duration of the force doesn't matter.
The cam holding power comes from the friction betwen the cam material and the rock. This is commanded by the angle of the cam.
To quote from the Wild Country cam book
"To go back to the friction test again, the same result would be obtained if
a block of alloy the size of a sugar cube or a block weighing two tons
were used. The angle at which the block will start to slip is independent
of the load applied. What this means in practice is that if you place a
Friend in a flare and pull on it, and it does not come out, (and so long as
you do not disturb the placement), the Friend will hold up to the limit of
the unit or the rock. "
placements fail when:
- irregularities in the rock prevent the piece from redistributing the force to the rock
- the stem is not aligned with the force (or the stopper is not aligned wiht the force)
- the rock fractures or crumbles
- the piece, due to above reason, moves out or extend beyond its range
- the cable breaks
A cam in standstone will leave groove as the rock "fails". As this failure is progressive, the shorter the duration the better (for a given force)
A cam in granite may flex a "spinter" one time too many.
Who knows the compression resistance for sandstone and granite ????
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rgold
Jun 2, 2004, 7:50 PM
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The most contentious issue in this thread has to do with the significance of the duration of forces during the arresting of a fall. Here are my opinions for the bonfire.
A number of posters have advanced the idea that the peak force acts for a longer time when there is more rope out but the fall factor is the same. This is not true; the peak force is an instantaneous event. The longer time spent arresting a longer fall (with same fall factor) means that it takes longer for the rope tension to build to the peak force, not that the peak force acts longer.
I think time variations are more properly viewed as a consequence of other processes rather than as the determining factor in fall arresting. As has been said and reiterated, the total potential energy of the leader's fall must somehow be "absorbed" by various kinds of work. The primary source of work is the work done in stretching the rope, but there is also the work done against frictional forces (which can be highly significant in the case of a dynamic belay), perhaps work done in elongating a screamer, and in the case of soft rock, the work done in dragging a piece through a yielding medium. The fall stops when the work done by the faller on various parts of the belay system adds up to the total potential energy, and time has no role in this summation.
This statement says nothing about the forces felt by faller and system, however. Assuming a successful catch, those forces are a result of the maximum tension developed in the rope, and this tension is proportional to the percentage elongation of the rope. It is this dependence on percentage elongation that ultimately accounts for the role of the H/L ratio as determining the maximum rope tension for a fall. Two falls with the same H/L ratio will stretch the rope by the same percentage and so will produce the same level of tension in the rope.
There were comments about bigger falls involving more potential energy. This is true, but longer lengths of rope allow the falling leader to do more work, because the work done depends on the actual elongation and not just the percentage elongation. This means that the bigger actual elongation corresponding to the same percentage stretch for a longer piece of rope allows the peak force to be the same, even though the fall is bigger, because more work can be done in stretching the rope.
Time variations correlate with but are not the determining factor in the peak tension achieved. The longer arresting times correspond to the fact that more distance is involved when a longer rope undergoes the same percentage elongation. However, if you stretch a rope by, say, 20%, the tension will be the same regardless of whether the stretching happened in a second or an hour.
As for gear failures in soft rock involving tracking, I don't think that the longer time involved in bigger falls with the same fall factor is an issue, because my understanding of the tracking phenomena is different, and I do know that, as mentioned, there is no peak force acting longer.
Here's what I think happens with tracking. There is a tracking threshold for the placement, i.e. the force at which tracking begins. I am going to assume for simplicity that this force remains approximately constant once tracking has begun. So what happens in a tracking failure is that the rope elongates until the tension creates a force on the piece equal to the tracking threshold. Once tracking begins, there is no further rope elongation; the rope tension remains at the level needed to initiate tracking. Energy absorbtion changes from rope elongation to the work needed to track the cam through the rock, a straight (force) X (distance) calculation if the tracking threshold is really constant. What you have, in effect, is a screamer, with tracking resistance replacing stitch ripping. Whether or not the piece fails depends on whether or not the work done in dragging it to the lip of the crack, when added to the energy absorbed by rope stretching up to the tracking threshold elongation, equals the potential energy of the fall.
Although I don't find validity in the time argument, I do agree, from the perspective of the analysis just given, that a big fall with a given fall factor is more likely to cause a tracking failure than a small fall with the same fall factor. This is because rope elongation up to the tracking threshold plus work done in tracking represents a fixed quantity of energy absorbed, whereas the bigger fall (with same fall factor) does have more potential energy to be absorbed. (The fact that there is more rope to absorb this additional energy does not intervene here because energy absorbtion has been switched to the tracking mechanism before the rope could do its job.) Thus the fall does not end with the tracking inside the crack and the piece blows. Note that the longer elongation time for the rope occurs before tracking begins and so has nothing to do with the ultimate failure of the piece.
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rgold
Jun 2, 2004, 8:22 PM
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The original question has to do with whether small cams are bombproof. Various replies suggest that there are a lot of definitions of "bombproof" in use. Some of these boil down to "it didn't fail when I/my friend/this guy I heard about fell on it." The fact that the same size cam did fail in similar falls doesn't seem to be part of this definition.
I propose that "bombproof" ought to mean "highly unlikely to fail under any conditions achievable in normal climbing circumstances."
I don't think this is an unreasonable definition, but it has as a consequence that bombproof placements are uncommon and
No small cam is bombproof.
Get used to it. This is life (and possibly death) in the real world. Climb accordingly.
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lambone
Jun 2, 2004, 8:27 PM
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In reply to: In reply to: Now I could be wrong here, but it looks to me that in this situation, you're rope is bomber, your biner is bomber, harness, sling... all bomber... but your cam is still not bomber.. Yeah, which is why I said: "if you're finding yourself exposed to possible factor 2 falls on a single micro cam, you might want to rethink what you're doing." Why would you ever take a fall approaching factor 2 on a single micro cam? P.S. check out the kn rating on a #3 wired nut. 5kn.
It is very possible. For instance, lets say you are aid climbing on some C3 pitch, and you take a daisy fall onto the tiny cam below you. Thiscould easily happen if you are not super carefull, and even if you are super carefull.
I think most of those very small pieces with low ratings are intended to be used primarily for bodyweight aid climbing placements. And many come with warnings that say something to that effect.
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alpnclmbr1
Jun 2, 2004, 8:31 PM
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Thanks Richard, a most informative post, as usual.
You have a talent for speaking of complex issues in laymans terms.
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tedc
Jun 2, 2004, 8:40 PM
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In reply to: Thanks Richard, a most informative post, as usual. You have a talent for speaking of complex issues in laymans terms.
Agreed.
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tedc
Jun 2, 2004, 9:05 PM
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In reply to: The most contentious issue in this thread has to do with the significance of the duration of forces during the arresting of a fall. Here are my opinions for the bonfire. A number of posters have advanced the idea that the peak force acts for a longer time when there is more rope out but the fall factor is the same. This is not true; the peak force is an instantaneous event.
Clarification: I don't think anyone, especially myself said that the "peak" force acts for a longer time. This is trivial but to say that would indicate a gross misunderstanding of the behavior of the forces in a fall. What was actually "advanced" was that the force will stay above an arbitraty threshold for a longer amount of time in a longer fall. i.e. if the max impact force for a ff 1 fall is 5KN then the force will be between 4 and 5KN for a longer amount of time in a longer fall. (same FF). I am not sure there was any confusion on this detail but just making sure.
rgold. I'll buy the explaination of the tracking cam acting just like a screamer.
Could you please apply your analysis to the case where the belayer is "peter pan'ed" higher off the belay due to a longer fall of same FF.
Also, how would you say a longer fall applies to the sequencial ripping of pieces in a 3 (or more) piece semi-equalized (cordalette) anchor. (Or does it?)
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curt
Jun 2, 2004, 9:35 PM
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In reply to: Clarification: I don't think anyone, especially myself said that the "peak" force acts for a longer time. This is trivial but to say that would indicate a gross misunderstanding of the behavior of the forces in a fall. What was actually "advanced" was that the force will stay above an arbitraty threshold for a longer amount of time in a longer fall. i.e. if the max impact force for a ff 1 fall is 5KN then the force will be between 4 and 5KN for a longer amount of time in a longer fall. (same FF). I am not sure there was any confusion on this detail but just making sure.
Ted, I did actually use the term "peak force" acting over a longer period of time several pages back, but I intended this to mean the same thing you are saying, as I thought would have been clear by my examples of potential failures that could occur in such scenarios. I guess I'll have to be a bit more careful with my choice of words. :wink:
Curt
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