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ambler
Nov 4, 2003, 8:21 PM
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In reply to: Ever notice, after a good hangdogging session, that when you rap off, the middle mark is off? The end of the rope you've been working stays longer for often as much as an hour...
So, what are the dynamic properties of a rope one second after it's been hit with a big fall? I'd be surprised if they're the same as an unstressed rope, but it seems we really need data here.
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curt
Nov 4, 2003, 8:27 PM
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Jay,
In reply to: The fact that the rope weakens with each successive UIAA test drop implies that even after five minutes, the rope has not fully recovered. How much will it have recovered in the tiny amount of time between the first piece blowing and the impact on the next piece?
Curt
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desertgranite
Nov 4, 2003, 8:29 PM
Post #78 of 91
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In reply to: The origonal question was this: "Is it just me, or does it seem that even lots of very experienced climbers have their pro zipper. I hear about it all the time; is it a matter of how it is placed, or gear failure, or...I don't seem to have a very clear picture on this yet. Any thoughts?" The correct answer is:...... it's just you sir. Zippered falls (zippers can move up or down, check your crotch to verify if in doubt about that) are uncommon, but tend not to be from experinced climbers when they occur. If you check out the stats from accidents of North am climbing: you will see there are many factors which cause death: lightning, exposure, stupidity, acts of nature like rockfall, and even falling. But statistically it is uncommon. Sorry to change the subject to the origonal question, I'm out for now. regards: Bill
lol
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jt512
Nov 5, 2003, 5:11 AM
Post #79 of 91
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In reply to: However, to whatever extent the rope does release its tension and "spring back," it does so very quickly. Curt
Can you document that substantial elasticity is not temporarily lost in the brief time that would elapse between two pieces of pro being impacted after the first one blew?
-Jay
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papounet
Nov 5, 2003, 5:29 PM
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In reply to: Jay, In reply to: The fact that the rope weakens with each successive UIAA test drop implies that even after five minutes, the rope has not fully recovered. How much will it have recovered in the tiny amount of time between the first piece blowing and the impact on the next piece? This is because some elasticity is permanently lost with each fall. In other words, a rope is not a perfectly elastic spring. After each UIAA fall, the rope is increasingly stretched. However, to whatever extent the rope does release its tension and "spring back," it does so very quickly. Curt
Same question here : which scientific data would make you think this ?
Over the years, I have read the UIAA magazine on equipment and tests, http://journal.uiaa.ch/download/20003.pdf,
http://www.uiaa.ch/commissions/links.asp?idobject=156
the manufacturer information (www.petzl.com simulator on fall factors )
some research paper
"an analysis of the loads in a typical climbing rope system subjected to a dynamic loading from a fall."
http://www.losalamos.org/climb/xRopes.pdf,
Italian Alpine Club test (both on tower lab and on real rock)
http://www.caimateriali.org/
or direct tests of rope strenghts :
http://www.xmission.com/~tmoyer/testing/
it seems clear to me that:
1. usage weakens rope (storage in good conditions doesn't, top-roping worse than rappelling, munther hitch worse than plate/tube systems,etc..),
2. the harder the fall factor, the more deformation to the rope (immediate and long lasting)
3. rope need time to recover after having dissipated energy (subjected to deformation take some time to recover).
4. 5 minutes is not enough for ropes tested under UIAA conditions (ff=1.78,etc...) to recover fully as shown by increasing energy transmitted to the climber during each additional fall, ending with ropes breaking up.
5. the fact that there appears to be a slight bounce of the rope after the maximal extension doesn't contradict this : the instant "spring back" you refer to does not indicate that the rope has gained back its energy-absorbion capability.
I suppose one could validate that with a simple setup :
ff= 2, 55 kg, half rope,
get a friend to help you set up a bench a 1 m and 1m50, 50 cm rope
now test to failure: install weight on higher board, make it fall, put it back as soon as weight stabilize, repeat and rinse
now redo the test, leaving 5 min between drops
now redo the test, leaving 10 min...
If you have access to a climbing gym, try two adjacent ropes (oneold/one new) when they change the ropes, and jump from the same place, and report back which rope absorb the most energy, which had lost its ability
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kyhangdog
Nov 5, 2003, 6:14 PM
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http://www.chockstone.org/Grampians/Members/NeilM/tower_fall_big.mpeg
Not zippered, but man place some gear. In my opinion if one is good, two is great.
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beaner_says_hi
Nov 6, 2003, 11:13 PM
Post #82 of 91
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How often do you guys replace your ropes, btw?
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cltclimber
Nov 7, 2003, 2:25 AM
Post #83 of 91
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In reply to: http://www.chockstone.org/Grampians/Members/NeilM/tower_fall_big.mpeg Not zippered, but man place some gear. In my opinion if one is good, two is great.
shooo....bad fall....that guy was really lucky. He stood up right away. No doubt he probaly injured his back pretty bad. But, it could have been much much worst
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curt
Nov 7, 2003, 2:47 AM
Post #84 of 91
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papounet,
In reply to: 4. 5 minutes is not enough for ropes tested under UIAA conditions (ff=1.78,etc...) to recover fully as shown by increasing energy transmitted to the climber during each additional fall, ending with ropes breaking up. 5. the fact that there appears to be a slight bounce of the rope after the maximal extension doesn't contradict this : the instant "spring back" you refer to does not indicate that the rope has gained back its energy-absorbion capability.
These points you make do not contradict what I posted. Rather, they reinforce my assertion.
As to your point (4), 5 minutes is not enough time "to recover fully" because the rope will NEVER recover fully. I thought I made that clear.
Regarding your point (5), the instant springback indeed does not "indicate that the rope has gained back its energy-absorbion capability." However, it has gained back what portion of the energy absorbing capacity that it will get back.
Curt
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curt
Nov 7, 2003, 2:50 AM
Post #85 of 91
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In reply to: In reply to: However, to whatever extent the rope does release its tension and "spring back," it does so very quickly. Curt Can you document that substantial elasticity is not temporarily lost in the brief time that would elapse between two pieces of pro being impacted after the first one blew? -Jay
No. I am basing my opinion solely on my understanding of basic physics and materials science. Can you document that elasticity IS temporarily lost in the brief time that would elapse between two pieces of pro being impacted after the first one blew?
Curt
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jt512
Nov 7, 2003, 5:32 PM
Post #86 of 91
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In reply to: In reply to: In reply to: However, to whatever extent the rope does release its tension and "spring back," it does so very quickly. Curt Can you document that substantial elasticity is not temporarily lost in the brief time that would elapse between two pieces of pro being impacted after the first one blew? -Jay No. I am basing my opinion solely on my understanding of basic physics and materials science. Can you document that elasticity IS temporarily lost in the brief time that would elapse between two pieces of pro being impacted after the first one blew? Curt
UIAA drop tests show that the impact force increases with successive drops made 5 minutes apart, implying elasticity is lost. If the rope doesn't fully recover after 5 min, I don't see how it could fully recover in the instant between impacting two pieces after the first one blew.
-Jay
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curt
Nov 7, 2003, 7:04 PM
Post #87 of 91
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In reply to: UIAA drop tests show that the impact force increases with successive drops made 5 minutes apart, implying elasticity is lost. If the rope doesn't fully recover after 5 min, I don't see how it could fully recover in the instant between impacting two pieces after the first one blew.
1) The rope doesn't fully recover (in your UIAA scenario above) in 5 minutes--and it never will. There are two components to the rope stretching and subsequently contracting. The first part is permanent stretch or elongation to the rope. If you measured the length of the rope after each UIAA test drop--you would see that the rope is actually longer after each drop. Five minutes has nothing to do with this type of elongation. If the thing sits there forever, that stretch will remain.
2) The "elastic" or non-permanent portion of the rope stretch (that is: the extent to which the rope WILL spring back) is the part that happens quickly.
Curt
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hugepedro
Nov 7, 2003, 7:23 PM
Post #88 of 91
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While I believe that a rope loses some of its elasticity that will take some time to recover, I also believe that it recovers a significant amount of elasticity very quickly. Otherwise, we'd be hearing about a lot more broken pelvises and lower back injuries in falls where the top piece pulls but the next piece holds.
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jt512
Nov 7, 2003, 7:25 PM
Post #89 of 91
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In reply to: In reply to: UIAA drop tests show that the impact force increases with successive drops made 5 minutes apart, implying elasticity is lost. If the rope doesn't fully recover after 5 min, I don't see how it could fully recover in the instant between impacting two pieces after the first one blew. In spite of my best efforts, you are still interpreting what I am saying incorrectly. So, I will try again. 1) The rope doesn't fully recover (in your UIAA scenario above) in 5 minutes--and it never will. There are two components to the rope stretching and subsequently contracting. The first part is permanent stretch or elongation to the rope. If you measured the length of the rope after each UIAA test drop--you would see that the rope is actually longer after each drop. Five minutes has nothing to do with this type of elongation. If the thing sits there forever, that stretch will remain. 2) The "elastic" or non-permanent portion of the rope stretch (that is: the extent to which the rope WILL spring back) is the part that happens quickly. Curt
I see what you are saying, but we're back to where we started from. You have no evidence that the rope will recover quickly enough, and it seems plausible that recoil from the first impact could actually increase the impact force on the second piece. This needs to be tested in a lab.
-Jay
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david.yount
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Dec 17, 2003, 1:14 PM
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In reply to: http://www.chockstone.org/Grampians/Members/NeilM/tower_fall_big.mpeg Not zippered, but man place some gear. In my opinion if one is good, two is great.
I think I see two pieces. At the end I think he says "well, my two bomber pieces decided to pull out...."
Regardless. Rather than sport quickdraws, if he had used full single-length runners or double-length runners his pro may have held. Just watch while he passes his pro; he's creating all sorts of horizontal tugging on his placements.
--David.
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luke
Dec 18, 2003, 4:34 AM
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Ok, so I hate to add to such a long ongoing discussion, but there is one other significant factor about rope recovery that has been left out so far, and that is HEAT. The energy of the fall goes into two things: permanent physical deformation of the rope (already much discussed) and heat. This may surprise some people, but if so you should ask yourself one basic physics question: the rope absorbed a lot of energy, not all of it as permanent stretching (because it "sprang back" somewhat, though we don't know how fast), so where did the rest of the energy go? The answer can only be heat, and in fact if you do enough drop tests on a piece of rope it will start to get warm. This seems like a silly thing to mention, except that when the core strands fail, they do not so much break as sort of stretch and melt. I can't say for sure that this would be relevant in the scenario under discussion because I haven't done any tests, but it might be that the heat from several falls temporarily affects the ability of a rope to absorb a shock. This would take some time to dissipate, certainly more than the time to the next piece.
Of course all of this is nice theory, but I too would like to know the results of genuine tests. There are fiber experts at MIT and Cornell. Does anyone know one well enough to ask?
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