MAXIMUM FORCE

Post by **ynot** » Fri Dec 12, 2003 3:14 am

I would think your harness would come apart before the rope snaped in 2.

Post by **Legion** » Fri Dec 12, 2003 4:37 am

You are probably right. I don't know what the standard is for harnesses off the top of my head. I think it is around 16 kN (not much sense in making a harness that will hold more than that since we already know what happens past that point....) maybe 16kN is for belay loops.

Post by **lordjim_2001** » Fri Dec 12, 2003 5:05 am

Don't know if it is standard but the Metolius Safe Tech Harness is rated at:

Rear haul loop 16kn
leg loop straps 6.6kn
belay loop 16kn
gear loops 10kn

from their 2003 cataloge

Post by **jeffers_mz** » Fri Dec 12, 2003 7:39 am

The problem with the engineer's data is the figure he uses for rope stretch. Very few ropes give figures for dynamic elongation, and the few I've seen that do give a figure for a factor 1.7 fall, the standard UIAA 80 kg fall. If you play with the equations, you find that dynamic elongation varies with the fall factor, in not entirely predictable ways. The rope is not a perfect spring, and near the extremes of its springlike behavior, dynamic elongation probably reaches an exponential variance with fall factor. Probably because right around here is where it will part.

I've come up with 12+ G being imposed on a climber in a factor two fall (using the dynamic elongation for a 1.7 fall factor fall) and 14+ G in falls with a fall factor over two (using the same figure). Given the nature of dynamic elongation's relationship with fall factor, the actual value will mitigate these forces somewhat, but the only way I know of to accurately calculate the forces involved is to test an individual rope.

The figure given when you buy nearly all ropes on the market currently is the static elongation, the percentage a rope will stretch with a dead weight hanging from it. It stretches a lot more when you fall on it than when you just hang. Dynamic elongation figures I've seen are about 31% for a factor 1.7 fall.

Post by **tomdarch** » Fri Dec 12, 2003 6:33 pm

Hmmm... Somewhere here in the stuff on my desk is the info from the Climbing Wall Industry group. They have info on what kind of load you need to design for when you design a climbing wall (or the building that the climbing structure is hanging off of). I don't remember the numbers, but I do remember that they were surprisingly small. Two or three thousand pounds is small potatoes in building design.

Also, we've been talking about gear failing at its rated strength. The rated strength has a type of safety factor built in. BD rates their biners with a '3 sigma' system. For a given batch of biners, the pull a sample group and test them to failure. You get a 'bell curve' of failure strengths, and they do some statistical analysis to come up with a mean (median?) failure strength and the standard deviation (sigma). They take three standard deviations down from the mean and that's the rated strength. The end result is that something like 99.99% of the biners from that batch will fail at a higher load - and the vast majority will fail at a much, much higher load.

Post by **captain static** » Fri Dec 12, 2003 6:53 pm

I know three people who have taken 150' falls. Two decked and the third hit the rope. I witnessed one of the falls. In that fall the person hit some tree branches on the way down, decked in a cloud of dust, and was staggering around but un-hurt when the dust cleared. The second person was climbing with a pack, had their helmet in the pack, and landed on their back. That person had eight broken ribs and a punctured lung, got up, walked out, got to the emergency room, & was climbing again within several months. The person who fell onto the rope had serious injuries and a prolonged recovery. I don't know if that person has ever climbed again since. So I guess if you are going to take the big screamer, it would be better to deck? At least the impact would potentially be spread out over more surface area.

Post by **Legion** » Fri Dec 12, 2003 8:08 pm

I fail to see your logic there. What caused the person who fell onto the rope to have injuries? Impact force? What was their fall factor? Were they using modern dynamic ropes and a seat harness?
Dan-O repeatedly took falls of that size and even bigger without injury. There are aid climbers out there who have zippered pitches as well and been unscathed.
I know that I would rather take 150' into space and bounce on the end of my dynamic rope then take 150' and hit the deck.

Post by **captain static** » Sat Dec 13, 2003 6:47 pm

The point is there is no logic to it. There are many factors other than the mechanics of the situation. Whether you survive such a fall or not may depend on dumb luck. I wish I knew more about the fall on the rope. I am positive the person was wearing a good harness and had a good rope. I don't know if they hit anything on the way down or at the end of the fall?

Post by **young'n climber** » Sat Dec 13, 2003 7:23 pm

What About Dan Osman? didnt he take big falls on ropes and other dangerous crap like that, how come his rope didn't snap (Yes Yes, i know his rope eventually did snap) but in his previous attepts his rope didn't snap and his body didn't break apart or any thing else along those lines

Post by **Yasmeen** » Sat Dec 13, 2003 7:26 pm

Legion wrote:Dan-O repeatedly took falls of that size and even bigger without injury.

That's who Legion was referring to, young'n. Same guy.