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Rope Impact Force and Gear Load

Original Post
rock-fencer · · Columbia, SC · Joined Dec 2009 · Points: 265

Has anyone looked at peak loads on gear in falls with respect to rope spec's of impact forces? i.e is their an actual force reduction with a lower impact force?

T

rock-fencer · · Columbia, SC · Joined Dec 2009 · Points: 265

yea i get that...im curious if peak loads on the top piece vary with ropes with different impact force specs. comparing the peak load on a bolt/piece with a rope witha 9 kN impact force vs 6kN impact force in a given fall situation.

would it have to reach the full impact force before any gains/losses are seen?

bearbreeder · · Unknown Hometown · Joined Mar 2009 · Points: 3,065

theres a reason why some ice climbers and mad brits prefer doubles on sketchy leads ... and it aint always because of wandering routes ;)

Jim Titt · · Germany · Joined Nov 2009 · Points: 490
rock_fencer wrote:yea i get that...im curious if peak loads on the top piece vary with ropes with different impact force specs. comparing the peak load on a bolt/piece with a rope witha 9 kN impact force vs 6kN impact force in a given fall situation. would it have to reach the full impact force before any gains/losses are seen?
This is something which I stopped discussing many years ago. The common belief (or assumption) is that a rope with a lower peak impact force will have the same charateristic through the entire load range and so a "soft" rope will give less force all the time. There is no real evidence whatsoever that this is so.
The belayer anyway has more influence on the impact force than the rope.
Tom Mulholland · · #1 Cheese Producing State! · Joined Apr 2010 · Points: 50
Jim Titt wrote: There is no real evidence whatsoever that this is so.
...which is really sad, because it'd be relatively easy and really fun to do. If somebody would give me a warehouse, 10 ropes, and a sensor, it'd be awesome to set up a really thorough statistical experiment.

  • edit: the warehouse is essential. There's no way I'm carrying 100 pounds of weights and a car battery up the trail again.
Raul P · · Unknown Hometown · Joined Feb 2013 · Points: 35

They talk about this a little in rock and ice

rockandice.com/lates-news/w…

The belay has way more of an impact:
Test Results

Static belay 1: 900 pounds force on the top piece of gear
Static belay 2: 900 pounds force
Static belay 3: 1,300 pounds force
Dynamic belay 1: 650 pounds force on the top piece of gear
Dynamic belay 2: 750 pounds force
Dynamic belay 3: 550 pounds force

bearbreeder · · Unknown Hometown · Joined Mar 2009 · Points: 3,065
Raul P wrote:They talk about this a little in rock and ice rockandice.com/lates-news/w… The belay has way more of an impact: Test Results Static belay 1: 900 pounds force on the top piece of gear Static belay 2: 900 pounds force Static belay 3: 1,300 pounds force Dynamic belay 1: 650 pounds force on the top piece of gear Dynamic belay 2: 750 pounds force Dynamic belay 3: 550 pounds force
careful with that one ... there are quite a few people here who are quite argumentative that dynamic belays do not reduce the impact force on gear ;)
todd w · · Unknown Hometown · Joined May 2008 · Points: 0

What I'm wondering is why they only did 3 trials of each.... Does it really take that long to rig up a weight and drop it? And no averages are calculated!

To a statistician, these values are considered "anecdotes" and are of very little value... hell, even the static belay jumped up 40% from one test to the next.

They should do it again, with 20 trials each. Calculate some averages and make a graph. Come on! They do that shit in 5th grade!!!

ZackBay · · Unknown Hometown · Joined Jan 2013 · Points: 10

Let me know if you can open this link it contains all math and physics equations you could possibly want for figuring out the impact forces. If the link doesn't work let me know I can send you a copy of it.
potomacmountainclub.org/ind…

rock-fencer · · Columbia, SC · Joined Dec 2009 · Points: 265
ZackBay wrote:Let me know if you can open this link it contains all math and physics equations you could possibly want for figuring out the impact forces. If the link doesn't work let me know I can send you a copy of it. potomacmountainclub.org/ind…
thanks Zack, the link works... i'll fiddle around and see what the math says.

nothing from rock and ice is exactly a reliable resource. I wonder if BD did some tests back when they were a Beal distributor

plugging some numbers in to excel this is what i got. Curious what real world difference might be...

Top Piece Tension IF FF
6.216647587 3.729988552 6.2 0.5
7.080482388 4.248289433 7.2 0.5
7.949406768 4.769644061 8.2 0.5
8.82165548 5.292993288 9.2 0.5
ZackBay · · Unknown Hometown · Joined Jan 2013 · Points: 10

No problem, glad I can help dude.

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,346
rock_fencer wrote:Has anyone looked at peak loads on gear in falls with respect to rope spec's of impact forces? i.e is their an actual force reduction with a lower impact force? T
Yes, I am conducting a quite long study on this actually. I started last year, but I had to stop my research for a couple of reasons. I am going to finish it this year. As far as I know, no one has conducted a truly detailed study of this phenomena in the field. Every detailed study related to fall dynamics that I have seen has involved a drop tower or something of the like. My study wont be amazing, but I do plan on testing a number of different ropes across many routes, many belay styles, many fall distances and fall factors and at least two climber weights. The ultimate purpose of my study will be to determine if the advantages of choosing a low-fall-factor rope over a high-fall-factor rope outweigh the disadvantages. The idea is to try to generalize the advantages and disadvantages by comparing impact force differences in reference to fall distance differences.
Matt N · · Unknown Hometown · Joined Oct 2010 · Points: 415
20 kN wrote: The idea is that a high-elongation rope will increase the chance of a piece of sketchy gear holding, but a low-elongation rope will increase the chance of you staying off the deck.
So, after each data point (leader fall), you switch ropes, clean and re-set the gear the exact same way it was placed before, making sure the rock or gear did not change in any way, and repeat the same fall dynamics in the same situation?

Pretty neat trick.
Geir www.ToofastTopos.com · · Tucson/DMR · Joined Jun 2006 · Points: 2,751

Here are some numbers that might be helpful:

A friend and I measured the peak force on the top piece in four scenarios:

Average peak force on the top piece when taking 10 foot falls with 50 feet of rope out: 820 pounds with a GriGri, 435 pounds with an ATC.

Average peak force on the top piece when taking 10 foot falls with 30 feet of rope out: 1030 pounds with a GriGri, 900 pounds with an ATC.

These measurements were done with a 10.5mm dynamic line, the climber was 150 pounds, the belayer was 170 pounds. Of course this is not definitive but it helps corroborate some of the other figures people have presented here.

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,346
Matt N wrote: So, after each data point (leader fall), you switch ropes, clean and re-set the gear the exact same way it was placed before, making sure the rock or gear did not change in any way, and repeat the same fall dynamics in the same situation? Pretty neat trick.
I am trying to determine, under real field conditions, how much of a difference in impact force there is on the top piece when comparing ropes of different types--exactly what the OP is looking for. But it sill be awhile before I am done.
NC Rock Climber · · The Oven, AKA Phoenix · Joined Dec 2009 · Points: 60

The one thing I have not seen tested is a Mammut Smart. They claim that it is the best of both worlds; assisted locking and some slip to minimize impact force. It would be great to see some data to prove or disprove this... Geir? 20 kN? Anyone?

20 kN · · Unknown Hometown · Joined Feb 2009 · Points: 1,346
John Wilder wrote: How can you do that and say with any real confidence that you found something significant if you do not replicate the conditions for each fall across a variety of ropes and belay styles?
Well, I will replicate the conditions as best as I can. With earlier testing I found that I can generally lob multiple near-identical falls on the rope and get a somewhat repeatable result. The results are close enough that, over the course of weeks of falls, if there is a note-worthy difference between the ropes I should see it.

Here is some very early testing I did on lead falls:

rockclimbing.com/cgi-bin/fo…;search_string=lead%20fall%20analysis;#2574668

It was far from a real study, but some may find it interesting.
Greg D · · Here · Joined Apr 2006 · Points: 883
Jake Jones wrote:Your question is unclear. It sounds like you're asking about a comparison of a piece that holds the fall in relation to max impact force on the rope? Max impact force, if I am not mistaken, is the maximum amount of force that the rope will transfer to the climber. However, this is rarely accurate because this is measured in the factory, on the first fall of a brand new rope. An older rope, or a rope that has seen a fall before, or one that has recently been fallen on will most likely have a higher max impact force on the climber than what the UIAA specification on the rope states. The top piece, in comparison, will always see a greater amount of force than the "max impact force" of a rope, because it feels force from both sides of the rope, the belay and the climber. How much more depends on the type of belay, conditions, etc. Your normal variable factors.
No. not right. But its late.
Jim Titt · · Germany · Joined Nov 2009 · Points: 490

The standard model assumes the rope stretch follows Hooke´s Law but with the modern generation of ropes this may not be the case. We also don´t know precisely how this changes with older ropes except that the impact force generally increases with use (falls).

Testing to get anything more than a generalisation is going to be difficult, time consuming and expensive especially with smaller falls as the tie-in knot, belay device and belayer themselves are the dominant factor, not the rope.
One could (and most of this has been done to a greater or lesser extent) test each part individually but this is only of use to indentify each effect and it´s imortance but combining them is not so easy since they interact with each other.
Then one needs to know how used ropes effect the situation since a new high-impact rope may well be better than a part-used lower impact one. All we need to do is get a selection of new ropes and "use" them in a controlled way, for example one set with repeated very small falls, loads of hanging on the rope and lowering down to represent working sport routes. Another set with medium falls and another set with fewer large falls.
To do this alone would take weeks if not months, ten or twenty simple drop tests a day with the data processing is good going on a drop tower.
Start adding in a selection of belay devices, different belayers and the need for some kind of statistically relevant repeats and the problems in time and manpower would be enormous.

We already know how to reduce the loads to a (near)minimum by allowing the rope to slide through the belay device as a good competition belayer would but quantifying this in any meaningful way is probably futile.

Geir www.ToofastTopos.com · · Tucson/DMR · Joined Jun 2006 · Points: 2,751
NC Rock Climber wrote:The one thing I have not seen tested is a Mammut Smart. They claim that it is the best of both worlds; assisted locking and some slip to minimize impact force. It would be great to see some data to prove or disprove this... Geir? 20 kN? Anyone?
I would be interested in checking that out.
Jim Titt · · Germany · Joined Nov 2009 · Points: 490
Jake Jones wrote: It's ok Greg, I'm all for learning, and not much for pissing contests. What I typed is my general understanding of it. Correct me if I am incorrect. I'll be grateful.
He probably means this bit "The top piece, in comparison, will always see a greater amount of force than the "max impact force" of a rope, because it feels force from both sides of the rope, the belay and the climber. How much more depends on the type of belay, conditions, etc. Your normal variable factors." which is of course not correct. For the great majority of falls the top piece is never loaded to anything like the the impact force rating of the rope, only for reasonable substantial falls is this the case.
Guideline #1: Don't be a jerk.

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