How much force can be generated in a sport fall

Regarding

Scott McMahon wrote:http://www.alpinedave.com/fall_machine.htm Fun stuff...

Greg D wrote:The fall distance is quite understated here. It merely doubles the distance above the last piece. This number will be larger due to amount of slack in system and stretch to mention a few.

Forget about errors in the fall height. The Alpine Dave fall machine is completely bogus. Stick with the Petzl calculator or learn how to do it yourself.

Thanks for the replies. Here is what I am trying to accomplish. I didn't give any specifics because I am wondering what the worst case scenario for a typical sport fall is. I am replacing a bunch of old crappy fixed draws in Rifle and I am wondering what size quicklinks I should buy. Most of what I have seen out there is 3/8 inch with about 2000 lb working load. Most of them are from the hardware store or an online dealer so I am not sure how accurate these numbers even are. So what do you think?

Jeremy H wrote:Thanks for the replies. Here is what I am trying to accomplish. I didn't give any specifics because I am wondering what the worst case scenario for a typical sport fall is. I am replacing a bunch of old crappy fixed draws in Rifle and I am wondering what size quicklinks I should buy. Most of what I have seen out there is 3/8 inch with about 2000 lb working load. Most of them are from the hardware store or an online dealer so I am not sure how accurate these numbers even are. So what do you think?

OHHHH! alrighty then!!!

go stainless to boot!!! its worth the extra $$$
but check it. that is awesome you are replacing stuff... but that will ahve to get replaced too eventually. rope grooves, and hanger grooves destroys either end of the draws/chains! i am doing some tests on ropes cutting over sharp edged rope grooves in biners.. stay tuned!

thanks!

Quick links have a safety margin built into their strength rating that is either 3:1 or 4:1, so that 3/8" quicklink is more like 6-8K.

Mark Nelson wrote: I'll offer the Petzl model is inadequate as well.

Inadequate in the sense that it is based on a simple model, but at least it correctly calculates the predictions of that model. The Alpine Dave model appears to be just plain wrong.

Alright so the questions come down to if I am going to buy 3/8" Quicklinks should I buy them online for $1, go to the hardware store and buy them for $2, or buy them from a climbing company for $4. I am trying to replace over a hundred draws so this will add up fast.

if you can find 1/2" on line for $1.50 or so, that would probably be a good option. like a few others said, that's great that you are motivated to do this. good luck and keep us posted.

3/8" links are huge. 1/2" are ridiculously big. 5/16" are the "normal" size.

If you're using chain you'll want to check with the locals - heavier chain and links are stronger, but give more rope drag. Often the lightest/smallest chain that is "safe" is what the locals will want.

Here is the site I was thinking about ordering from:

stageriggingonline.com/chai…

The 3/8" have a working load of 2200 lbs for $1
The 1/2" have a working load of 3300 lbs for $1.75

Jeremy H wrote:3/8" for $1

thats my vote.
bonus if you get donations from the 'locals'.

EDIT: those will outlast several iterations of dogbones on the draws, and even moreso than the biners that (never) get replaced...

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Dave force calc is actually good...he just put in the wrong elongation. Most dynamic ropes stretch about 33%. He recommends a near static rope elongation. His calculations aren't real-world, but it's not that far off.

The take home message is that the ropes do their job and keep the impact force at their stated values as long as you don't fall on the rope more than what is recommended, you won't have and surprises. Moral of the story...bolts are strongest.

Referring to the original thread, I've had 5/8" links pull apart in pull testing and drop testing. The mode of failure was the the threads didn't hold - a carabiner is a much better choice. I understand the dilemmas of permanent draws, but the quick links just aren't as strong. I've seen them come undone over time as well. I glue mine together in hopes that this won't happen, but I know it's just a facade.

Sport climbing falls don't produce that much impact force unless you're in a multip-pitch situation and fall past your belayer. But then we're also talking about sport climbing and that implies BOLTS. Bolts are way stronger than gear, ice screws, etc... Don't worry about it and you'll climb harder!

Marc Beverly wrote:Dave force calc is actually good...he just put in the wrong elongation. Most dynamic ropes stretch about 33%. He recommends a near static rope elongation. His calculations aren't real-world, but it's not that far off.

No, it is completely bogus.

First of all, if by elongation is meant the elongation experienced in stopping the fall, that elongation has to be part of the calculation, since it is different for different falls. You don't enter it. Knowing that elongation ahead of time is equivalent to knowing the maximum rope tension during the fall, in which case you don't need the calculator.

If you nonetheless try a UIAA standard fall with 33% elongation, the calculator will not return a value.

So it can't be the fall-arresting elongation that is supposed to be entered. And the calculator won't accept the maximum elongation under the UIAA drop test conditions either.

The only elongation that fits the range suggested is the value for elongation under body weight. This can in fact be used to calculate the rope modulus, but it is an inaccurate way to do it because the rope's behavior at small loads is a bit different.

In any case, the values returned by the calculator make it clear that the basic rope physics has not been derived from the elongation number. Falls with an 80 kg weight approaching fall factor 2 give tensions like 16 kN, somewhere around double the value for any real rope. The calculator simply gives incorrect values, and when you are off by as much as a factor of two, that does not qualify as "not far off."

Yes, totally bogus.

Hi marks to Geir for actually submitting real life empirical data. Has anyone proof tested or failure tested crag bolts? I'd like to test my own in-situ bolts (just so I can sleep easier). I think I know how I want to do it. If anyone can direct me to another thread or has experience I'd love to hear it.
Thanks,

One thing about the alpine Dave fall calculator is that 6-9% elongation is much closer to a static rope than a dynamic rope. Dynamic rope elongation is much closer to 30% or am I missing something?

Darren Mabe wrote:us enginerd types may need a little more information than that. length of fall? angle of rock face? weight of both climbers? kind of rope you are using? fall factor? kind of belay device? kind of belay style? etc. is said fall taking place on earth? moon? mars? EDIT: or if you are extremely bored check out: petzl fall simulator

These are questions every lead climber should be asking. It's the enginerds that actually come up with the answer. More timid climbers just put in another piece...

BrianH wrote: These are questions every lead climber should be asking. It's the enginerds that actually come up with the answer. More timid climbers just put in another piece...

It's sport climbing ie bolted face they can't put in another piece. Sooo the more timid climber stick clips the next bolt.

So the question is how much force in a top rope fall.

Fleetwood Matt wrote:Hi marks to Geir for actually submitting real life empirical data. Has anyone proof tested or failure tested crag bolts? I'd like to test my own in-situ bolts (just so I can sleep easier). I think I know how I want to do it. If anyone can direct me to another thread or has experience I'd love to hear it. Thanks,

In the Muir Valley in the RRG I have seen remnants of testing of in-situ bolts. I believe Mr. Weber uses a winch of some sort. I don't know a ton about it and would be interested in hearing from someone who does.

Jace Mullen wrote:One thing about the alpine Dave fall calculator is that 6-9% elongation is much closer to a static rope than a dynamic rope. Dynamic rope elongation is much closer to 30% or am I missing something?

You seem to be missing the posts explaining that the Alpine Dave Calculator is completely worthless.