Forums: Climbing Information: General:
How much force is actually put on your gear?
RSS FeedRSS Feeds for General

Premier Sponsor:

 


UpToTheOzone


Aug 15, 2012, 6:47 PM
Post #1 of 15 (2818 views)
Shortcut

Registered: Aug 28, 2011
Posts: 50

How much force is actually put on your gear?
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

A friend of mine who I'm introducing to climbing was asking if there is a calculation to find the amount of force being placed on a piece of gear when I leader takes a fall. I assume the answer is, it depends, how much rope is out, what is the max impact force of the rope, did the belayer give a soft catch, and so on.

Is there an equation or an answer to this? or is it just: It depends


zxcvbnm


Aug 15, 2012, 10:01 PM
Post #2 of 15 (2773 views)
Shortcut

Registered: Nov 12, 2011
Posts: 16

Re: [UpToTheOzone] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

I think that an equation that took all the factors of real life into account like friction of the rope through carabiners and over rock, the amount of belay device slippage and give in bodys and harnesses, would be rediculously complicated and hard to measure and apply.

In general normal real world falls (typical sport or trad falls) have been measured around around 2-7 kn at the top piece

A short low fall factor fall with a newish rope might give 2 or 3kn at the top piece where as a really hard fall with an old rope belayed with an autolocking device might even approach 8 or 9kn.

So it basically depends on the situation


moose_droppings


Aug 15, 2012, 10:23 PM
Post #3 of 15 (2764 views)
Shortcut

Registered: Jun 7, 2005
Posts: 3349

Re: [UpToTheOzone] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

UpToTheOzone wrote:
A friend of mine who I'm introducing to climbing was asking if there is a calculation to find the amount of force being placed on a piece of gear when I leader takes a fall. I assume the answer is, it depends, how much rope is out, what is the max impact force of the rope, did the belayer give a soft catch, and so on.

Is there an equation or an answer to this? or is it just: It depends

Try this.


jowybyo


Aug 16, 2012, 6:09 AM
Post #4 of 15 (2719 views)
Shortcut

Registered: Aug 6, 2012
Posts: 20

Re: [UpToTheOzone] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Normally in engineering problems, we are only concerned with worse case situations. This usually allows us to ignore things such as friction, soft catches, unknown variables, etc. Also, we utilize a safety factor to cover anything we missed (i.e. multiply the max load by 2 to be sure it's larger than any real world possible situation).

Check out these links for the basic physics and equations for calculating fall forces.

http://www.google.com/...I2vKxKEaK6dxEJkGiK_Q

http://www.google.com/...rkxPIGhp64Qxh54a0tRg

-Joe B.


USnavy


Aug 16, 2012, 3:46 PM
Post #5 of 15 (2634 views)
Shortcut

Registered: Nov 5, 2007
Posts: 2660

Re: [zxcvbnm] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (2 ratings)  
Can't Post

zxcvbnm wrote:
where as a really hard fall with an old rope belayed with an autolocking device might even approach 8 or 9kn.
The only way you are going to get forces that high is on a near factor two fall. I did some testing on lead falls awhile back, and with a very hard catch on a locking belay device, with a fall on the first bolt, using a rope with an impact force rating of over 10kN, I barely broke 4kN on the top piece.

Here is a link: http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2574722;search_string=lead%20fall%20analysis;#2574722

Also, those calculators seriously overestimate the impact force when compared to real-world falls. Real-world falls can produce half of what the calculator will predict. The problem is the calculator cannot account for very many variables, so it assumes the belay is completely static and it assumes the person is a steel weight. Well, an 80kg rigid mass will produce about as much force as a 100kg flexible mass, such as a person. Also, the belay style has a huge effect on the impact force on the top piece. As you will see in the link, the difference between a hard catch and a soft one amounted to +21% impact force, and a hard catch with a real belayer is still softer than a completely static catch.


(This post was edited by USnavy on Aug 16, 2012, 7:05 PM)


Partner rgold


Aug 16, 2012, 5:35 PM
Post #6 of 15 (2601 views)
Shortcut

Registered: Dec 3, 2002
Posts: 1800

Re: [jowybyo] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

jowybyo wrote:

Check out these links for the basic physics and equations for calculating fall forces.

http://www.google.com/...I2vKxKEaK6dxEJkGiK_Q

http://www.google.com/...rkxPIGhp64Qxh54a0tRg

-Joe B.
Readers might want to know that Curtis (ignoring years of exposition of this material and faiing to credit the innovators, Arnold and Wexler in 1946) uses his own non-standard definition of fall factor. The equation he gets is equivalent to the standard equation, but uses his useless fall factor instead of the correct one. (It is of some slight mathematical interest that the wrong fall factor can be used to obtain the same results one gets with the correct fall factor.)

The reason the Curtis fall factor is worthless is that it includes rope stretch, whereas the classical fall factor does not. Including rope stretch means that it is impossible to know from the position of the leader relative the the protection and the belayer what the fall factor is, since the Curtis Fall Factor requires knowledge of the maximum rope stretch, something that could only be determined under sophisticated laboratory conditions.

if you want to learn the derivation of the standard equation, the links provided above are not the way to do it, since no one else in the universe means what Curtis means when he speaks of the fall factor. I suggest my account, available from this site at http://www.rockclimbing.com/...ment;postatt_id=746) and JT512's account, which adds the effect of friction, at http://jt512.dyndns.org/impact-force-rev1.pdf

The standard equation is just the first step in a process of obtaining more complex equations that account for more of the factors found in the field.


(This post was edited by rgold on Aug 16, 2012, 5:38 PM)


zxcvbnm


Aug 16, 2012, 5:41 PM
Post #7 of 15 (2595 views)
Shortcut

Registered: Nov 12, 2011
Posts: 16

Re: [USnavy] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

What condition was your rope in that test? Some of my old ropes have been almost painful to take significant falls on.

I shouldn't have described that situation so specifically or limited it to what i said. (I did say "might even approach" and "really hard fall" aka "near factor two fall")

Imagine climbing on a beat up not so stretchy rope and being belayed by a grigri off the anchor, then taking a 1+ factor fall or something. Or even being belayed conventionally on the same rope and having the rope run over a rock volume or something just before the top piece and having a massive amount of friction at that point. 7-8ish kn might be really rare but I bet it happens.


USnavy


Aug 16, 2012, 7:10 PM
Post #8 of 15 (2569 views)
Shortcut

Registered: Nov 5, 2007
Posts: 2660

Re: [zxcvbnm] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (1 rating)  
Can't Post

zxcvbnm wrote:
What condition was your rope in that test? Some of my old ropes have been almost painful to take significant falls on.

I shouldn't have described that situation so specifically or limited it to what i said. (I did say "might even approach" and "really hard fall" aka "near factor two fall")

Imagine climbing on a beat up not so stretchy rope and being belayed by a grigri off the anchor, then taking a 1+ factor fall or something. Or even being belayed conventionally on the same rope and having the rope run over a rock volume or something just before the top piece and having a massive amount of friction at that point. 7-8ish kn might be really rare but I bet it happens.
Well I recently retired a rope that was about ten years old, it had caught over 500 lead falls and 1000+ TR falls. I also used it to rap and ascend. It was rated as a 10.5mm rope, but my caliper put it at about 13mm right before I retired it. I think it is safe to say it was overused and well in need of retirement. None the less, falling on it was no worse than falling on the rope I quoted in my last post. Indeed it was worse than it was when it was new, but the rope I used has one of the highest impact forces of any rope on the market, so it would be hard for any other rope to keep up. Anyway, even with a very used rope, I think it would be very hard to achieve forces that hard on a single pitch climb. I think the only way you are going to get that is if you fall past the belay, or you weigh 200 lb+ and take a fall on the first bolt with a hard catch.

But indeed, as you said, 8-9kN can happen, and I am sure it has. But as far as craging at your local sport crag and taking a whipper that will produce that much force - I do not think it is going to happen.


zxcvbnm


Aug 16, 2012, 10:31 PM
Post #9 of 15 (2528 views)
Shortcut

Registered: Nov 12, 2011
Posts: 16

Re: [USnavy] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

So was the rope in your test fairly new?

I agree that 8-9kn won't be something you see at the sport crag or maybe even single pitch.

From my experiences I strongly suspect that some ropes lose their stretch a lot more than others. I recall jt512 saying that was one of reasons he prefers beal.


USnavy


Aug 16, 2012, 11:12 PM
Post #10 of 15 (2521 views)
Shortcut

Registered: Nov 5, 2007
Posts: 2660

Re: [zxcvbnm] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (2 ratings)  
Can't Post

zxcvbnm wrote:
So was the rope in your test fairly new?

I agree that 8-9kn won't be something you see at the sport crag or maybe even single pitch.

From my experiences I strongly suspect that some ropes lose their stretch a lot more than others. I recall jt512 saying that was one of reasons he prefers beal.
Well, whether the crag is sport or trad is irrelevant, a fall of a certain fall factor on a piece of trad gear will not be noticeably different than one on a bolt unless the piece slips.

As far as the rope goes, it was reasonably new, it probably had about 40 lead falls on it.

As far as rope stretch with time goes, it seems ropes stretch more with time, not less. Or at least their static elongation increases. I own something like 14 ropes. Some are brand new, others are in poor condition. One thing I have noticed with all of them is as time goes by and they get used more and more, falls on TR become longer, not shorter.

However, their impact force increases as well. It is kind of contrary to see a rope increase in both elongation and impact force, but it is possible. Basically, it seems as when a rope gets older and stretches more, when you first load the rope it stretches a lot but it does not really carry much of the load. As the rope stretches more and more the elasticity, or stress strain curve, suddenly changes and the rope carries a larger sum of the load without stretching much more. That is how it is possible for a rope to stretch a lot but still have a high impact force.

Granted, that is just my thoughts on the issue, it is not necessarily fact, I haven't tested it. But one thing I am positive of is that all of the ropes I have retired had a much higher static elongation right before retirement time than they did when they were new.


(This post was edited by USnavy on Aug 17, 2012, 8:13 PM)


jowybyo


Aug 17, 2012, 5:56 AM
Post #11 of 15 (2486 views)
Shortcut

Registered: Aug 6, 2012
Posts: 20

Re: [rgold] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Thank you for pointing that out. Your references, particularly the paper you wrote, are fantastic.

I would encourage the rest of the us to read the papers posted by rgold so we can all understand the physics and consequences of a leader fall.

Thanks rgold. I wish I had you as a math professor in college. If you have any other papers detailing math related to climbing, I would enjoy the reading.

-Joe B.


Partner cracklover


Aug 17, 2012, 8:35 AM
Post #12 of 15 (2455 views)
Shortcut

Registered: Nov 14, 2002
Posts: 9999

Re: [moose_droppings] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

moose_droppings wrote:
UpToTheOzone wrote:
A friend of mine who I'm introducing to climbing was asking if there is a calculation to find the amount of force being placed on a piece of gear when I leader takes a fall. I assume the answer is, it depends, how much rope is out, what is the max impact force of the rope, did the belayer give a soft catch, and so on.

Is there an equation or an answer to this? or is it just: It depends

Try this.

The above link is excellent, and is the best tool for a first approximation.

In the field, there are typically two things that will cause a significant variance from the results shown in JT512's calculator:

1 - Dynamic belaying. This is an advanced belay technique, in which either some rope is allowed to slip through the device as the force comes on it, or the belayer jumps as the force comes on her. This will somewhat lower the peak forces.

2 - Rope friction. When the rope runs diagonally between pieces of gear, or runs around an overhang, this can add significant friction to the system. This lowers the peak force on the belayer, but raises the peak forces on both the climber and the gear that holds the fall.

One force that can also have a small effect, but one that can potentially be significant is knot tightening. In a fall, the climber's knot tightens, "absorbing" some energy. While the amount of energy "absorbed" in this way is fairly small, it can be enough to make a small but significant change to the peak force felt in a short fall. This is because the amount of total energy in the system in a short fall is relatively small, so the amount of energy "absorbed" by the knot tightening is a small but significant ratio of the energy in the system.

As you can see, some of these things will raise the forces felt on your gear relative to what the calculator shows, while others will lower it. So on the whole, for an average fall, the calculator will give forces that are similar to what you would see in the real world.

As it happens, it also agrees with all of the calibrated tests I've seen documented in the real world.

GO


zxcvbnm


Aug 17, 2012, 7:07 PM
Post #13 of 15 (2397 views)
Shortcut

Registered: Nov 12, 2011
Posts: 16

Re: [USnavy] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (0 ratings)  
Can't Post

Sorry, I meant to imply "at the crag" obviously there wouldn't be much of a difference between sport and trad. By loss of stretch I did mean higher impact force and less comfy falls, not just elongating more.

Did you ever do anymore testing with your strain gauge? I always find real world forces interesting.


http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=408931;search_string=how%20many%20lead%20falls%20can%20a%20rope%20take;#408931

In this thread (near the bottom of the page) it seems the rope's impact force only increased by 1 kn or so in the middle where the wear could mostly be lowering and rappelling. What do you suppose the impact force would've been on the end section (that was getting the abuse from lead falls) if it would've survived a drop and not broken at 7.45 kn?


USnavy


Aug 17, 2012, 11:55 PM
Post #14 of 15 (2370 views)
Shortcut

Registered: Nov 5, 2007
Posts: 2660

Re: [zxcvbnm] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (2 ratings)  
Can't Post

zxcvbnm wrote:
Sorry, I meant to imply "at the crag" obviously there wouldn't be much of a difference between sport and trad. By loss of stretch I did mean higher impact force and less comfy falls, not just elongating more.

Did you ever do anymore testing with your strain gauge? I always find real world forces interesting.


http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=408931;search_string=how%20many%20lead%20falls%20can%20a%20rope%20take;#408931

In this thread (near the bottom of the page) it seems the rope's impact force only increased by 1 kn or so in the middle where the wear could mostly be lowering and rappelling. What do you suppose the impact force would've been on the end section (that was getting the abuse from lead falls) if it would've survived a drop and not broken at 7.45 kn?

I do not know how much the impact force would be if the rope did not break, no one does. But I dont think it would be any big shocker number, maybe 9 kN tops. I find this article very interesting because it is directly contrary to an article that the UIAA produced awhile back. The UIAA wrote an article that said something along the lines of it being impossible for a rope to fail on a single UIAA drop. They said they tested countless used and old ropes, one as old as 20 year, and in all cases the ropes held at least one UIAA fall. The UIAA may be interested in reading this BD article if that rope did fail on the first drop.

I have done lots of other testing with my load cell, some of which I published, a lot of which I have not. I plan to do much more in depth testing on lead falls in the real world later. I want to compare high and low impact force ropes and hard and soft catches in the real world to determine how much of an influence they have on the force subjected to the top piece. I suspect that having a high elongation rope wont lower the impact force on the top piece as much as most people think, especially when a soft catch is given. But we will see.

cracklover wrote:
moose_droppings wrote:
UpToTheOzone wrote:
A friend of mine who I'm introducing to climbing was asking if there is a calculation to find the amount of force being placed on a piece of gear when I leader takes a fall. I assume the answer is, it depends, how much rope is out, what is the max impact force of the rope, did the belayer give a soft catch, and so on.

Is there an equation or an answer to this? or is it just: It depends

Try this.


So on the whole, for an average fall, the calculator will give forces that are similar to what you would see in the real world.

As it happens, it also agrees with all of the calibrated tests I've seen documented in the real world.

GO
No it does not, I just got done proving it. That calculator will predict the maximum possible impact force in the system, not the average. It assumes a completely static belay, and I believe it assumes a rigid mass sliding down a completely straight path that is absolutely parallel with the top piece. None of those three predictions are realistic of a standard lead fall in the real world.

As far as the calibrated real world tests you are referencing, I would really like to see them because as far as I know, they dont exist, at least not many do. That is the entire reason why I bought my strain gauge analyzer. I wanted to conduct real world lead fall tests. I searched Google high and low looking for real world tests and I dident find any. I found tons of tests from BD and others conducting so called "real world" replica tests. But they were in a drop tower, using a static belay and a rigid mass - not even remotely real world. Real world means a person for the belayer and the climber, and a crag to fall at. Drop towers cannot replicate real world results. Most people who conduct lead fall testing do it in a drop tower because having a static mass and fixed belay is imperative for repeatability which is necessary to properly compare two different scenarios in most cases.

That calculator is giving me predictions in excess of 7 kN for falls that produced less than 4 kN when I tested them at the crag with me as a weight and another climber as a belayer. In fact, to completely be sure that my data was accurate and the calculator was not (not accurate for real world applications), I used a load limiter on the bolt. I took a piece of thin cordlette and tied it to the bolt. I repeatedly pull tested replica samples using the exact same biners I used in the real test and I came up with an average failure strength of just under 5 kN. So had the calculator been right and my load cell been wrong, the cordlette would have failed, but it dident, not in any of my tests.

The calculator seems to be accurate when comparing falls conducted in drop towers. I would expect it would be as that is what it is modeled off of. But real world falls at the crag are just too different to be comparing with drop tower tests.


(This post was edited by USnavy on Aug 18, 2012, 12:06 AM)


JimTitt


Aug 18, 2012, 1:18 AM
Post #15 of 15 (2359 views)
Shortcut

Registered: Aug 7, 2008
Posts: 977

Re: [USnavy] How much force is actually put on your gear? [In reply to]
Report this Post
Average: avg_1 avg_2 avg_3 avg_4 avg_5 (2 ratings)  
Can't Post

The big question is why?
Why do you want to know a possible value for a possible scenario that may or may not occur and probably could never be accurately quantified anyway?

Your "real world" is not mine since I weigh considerably more than you and I know even heavier climbers still, even ones that carry rucksacks full of gear as well. My real world also includes on the odd occassion being 40m out from my last piece, something I doubt you are going to test. The UIAA wisely realise that the "real world" can be a big place, not just slumping on a bolt and designed the standards back then to cater for the largest realistic climber weight and the worst possible case and this is the correct approach.

The factors which may increase or decrease the load on a (marginal) piece of gear are well established and one can merely hope one has applied these correctly and the placement was up to expectations, no knowledge of the magnitude of the forces involved helps in any way.

You say "Drop towers cannot replicate real world results." but of course they do, as accurately as possible replicating the worst case for one senario which has historically been proven to give safe ropes. Conversely real world testing cannot replicate drop tower tests as willing volounteers are somewhat rare.

There are instrumented "at the crag" tests but Google won´t find them, not everything in this world is on the internet, in English or published for general consumption (or Google may decide not to show you them as they are hosted on a competitors server and block their advertising).


Forums : Climbing Information : General

 


Search for (options)

Log In:

Username:
Password: Remember me:

Go Register
Go Lost Password?



Follow us on Twiter Become a Fan on Facebook