No, but it's trivial to calculate the peak force. All we need to know is the UIAA impact force rating of the rope (which allows us to calculate the rope's modulus of elasticity), the weight of the climber, and the fall factor. If the rope has been clipped through an anchor, we can add in the "pulley effect" after adjusting for friction through the anchor. The result will be the maximum impact force assuming a static belay and no other frictional forces in the system.

If I remember right you use a retasked digital crane scale to get your force measurements? Not to be picky, but those won't work for measuring peak force during a fall and your results are most likely well under the true peak force.

Crane scales simply don't have a high enough scan rate on the force measurement (often only 10 samples/second) for this sort of thing and to do it properly you need something with a scan rate several orders of magnitude higher or an analog peak capture channel.

-aric.

EDIT- if you keep an eye on Ebay you can usually pick up a used Daytronic 4077 strain gage indicator for $250 or so and they're perfect for this sort of thing since they have a digital scan rate of 1000 samples/sec and an analog peak capture channel. Plus it will most likely work with the load cell you already have from the crane scale. They're a bit of work to get programmed for this kind of thing, but its not too bad once you read the manual a couple times. Heck, depending on what you want it to do I could just send a copy of my config that you could load onto it.

Try 2:

Real world forces will never approach the value calculated with the fall factor formula.

Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath.

-a.

I haven't looked at the paper Majid referenced. I suppose that in principle you could define fall factor either way, but I would think that defining it in terms of maximum stretch would complicate the derivation of the equation for maximum impact force from Hooke's Law.

Edit: Glancing at that paper, the author's expression for the maximum impact force, based on the total distance fallen (including maximum rope stretch) is actually simpler than the one based on the "free fall" distance.

Jay

Aric

This is unfair that I am always the black sheep in RC.Not my fault that a single page n00bee question turns in to full blast scientific hell but to add a little heat in to this stew, I am adding few photos.

[IMG]http://img254.imageshack.us/img254/6869/scan0002gfn.jpg[/IMG]

[IMG]http://img26.imageshack.us/img26/4138/scan0003y.jpg[/IMG]

[IMG]http://img26.imageshack.us/img26/4991/scan00041.jpg[/IMG]

[IMG]http://img21.imageshack.us/img21/295/scan00051.jpg[/IMG]


[IMG]http://img21.imageshack.us/img21/8718/scan00061.jpg[/IMG]


[IMG]http://img8.imageshack.us/img8/1286/scan0007c.jpg[/IMG]

[IMG]http://img8.imageshack.us/img8/8462/scan00081m.jpg[/IMG]

[IMG]http://img22.imageshack.us/img22/415/scan00091.jpg[/IMG]

Majid, you are the true master. I'm sorry for spoiling it, but 5 pages and counting... damn.

I'd call you out as a troll, but you seem to have a knack for picking topics that everyone thinks are common knowledge and then all hell breaks loose when people realize that not everyone thinks as they do. I'm still not 100% sure anyone actually benefits from the resulting arguments, but they sure are entertaining. And if you look past the arguments, quite informative.

I won't go so far as to tell people to back off as was requested by another user in S&F since you seem to bring a lot of this on yourself, but I will gladly sit back and enjoy the aftermath.

-a.

Not all strain gage indicators are made equal... some are intended for static loads and have low scan rates, which could explain the lack of discrepancy with the crane scale.

I'm going to be offline for the next couple days, but it boils down to the fact that reading an analog peak with digital equipment is suspect unless you get into extremely fast (expensive) scan rates. I don't know what gear you're using, but frankly I'm not happy with the 1000 samples/sec I get with my Daytronic gear and if you're less than that I don't have much faith in your results. Analog is where its at as far as this is concerned and without data proving digital is good enough I'm not convinced. Fortunately (for me) my gear gives both, hence the lack of faith in the digital.

-a.

So Jay, you are saying if this climber who was linked with a biner that was rated to lets say 5 KN and then his belayer was also was tied in to a fix anchor with 5 KN biner, the leader's biner has a higher chances of failure than belayer biner.

Now is this because the draw(B) is taking some of the load therefore, the bottom half of rope(belayer C) does not get the forces as equal as the other half ( leader side A)?

For efficiency, I won't remove the dots. However, I encourage everyone to hit "page down" or "page up" while looking at those photos. It's fun.

Well the one I have says it scans at 1000 cycles a second and the manufacturer said it’s an appropriate choice for capturing dynamic loads. Why are you not happy with your Daytronic strain gauge? Do you think 1k scans a second is not enough?

I may have been unclear Majid... I don't think you're a troll, rather that I suspect that you know far, far more than you let on and make your posts intentionally vague and confusing to get the discussion going about the point you're trying to make. I've been following your threads for years now and I'm convinced of this.

You take far more heat here on RC than you deserve and I'm hoping that everyone else finally figures out what's going on and backs off. (HINT HINT)

-a.

Well, my recollection of basic information theory is that you want your sampling rate greater (by at least 2 times?) than the time of the event you are trying to capture. So, what is the duration of the peak load?

It's instantaneous. I guess he's screwed.

Jay

So, that just means he needs something that reads twice as fast as 0.0000 seconds.

Seriously - the peak load must occupy some finite time. Otherwise not even analog measuring devices would accurately capture it. Also, in a fall, the greater the kinetic energy (larger mass, longer fall), the greater time over which the load occurs.

If the peak force is instantaneous (and I think it is), then you can't capture it. But if readings are taken 1000 times per second, then you can measure the force within 1/2000 of a second of the peak force, which, hopefully, is good enough.

Jay

Umm, within 1/500 th of a second.

No. If the time at which the maximum force occurs t is in the interval [0, .001s], then

max(min{t, .001s–t}) = .0005s.

That's 1/2000 of a second.

Jay

It's on like Donkey Kong!!!

If the peak force is instantaneous (and I think it is), then you can't capture it.