I recently purchased a 500Hz. strain gauge analyzer and 5000 lbs load cell that I can use in the field with my laptop, so I decided to do some testing on TR falls today. This is just some quick non-scientific testing to familiarize myself with the equipment, so don’t take anything in here too seriously. I took six falls of varying length and catch method (i.e. hard catch, soft catch, ect.). The graphs below represent the most serious of the six falls. Basically I wanted to determine what would be the highest impact force I could produce on the anchor while top roping without doing something extremely dumb, like taking a huge TR whipper on static rope.

Here are the specs:

-160 lb climber
-175 lb belayer
-Mechanically locking belay device
-9.9mm Maxim Glider, 9.5 kN impact force rating, 29% dynamic elongation, 5% static elongation
-Hard catch (the belayer just stood there and locked off)
-50 feet of rope out, 12 foot free fall, 20 foot total fall distance (approximate, not measured)

To start with, some really crappy pictures of the set up:
[img]http://img209.imageshack.us/img209/5091/1001093b.jpg[/img]
[img]http://img696.imageshack.us/img696/5688/1001096h.jpg[/img]
Next, the fall graphed out:

[img]http://img338.imageshack.us/img338/8853/totalg.jpg[/img]

This next graph represents the loading that was in the upper 50% of the fall range. The peak load was just shy of 700 lbs. so this graph shows the loading above 350 lbs. The numbers on the X axis represent the duration in milliseconds multiplied by ten.

[img]http://img3.imageshack.us/img3/5476/53675516.jpg[/img]

This last graph captures what I am going to call the “high” or “mean peak” meaning it shows how long the force stayed in the upper 10% range of the fall range, or above 600 lbs. This graph would be useful to compare different falls of the same fall factor, but different fall lengths, because it shows how long the anchor experiences the peak force of the fall. As you can see the loading on the anchor was only in the top 10% for 160mS.

[img]http://img52.imageshack.us/img52/2038/peek10.jpg[/img]

So the maximum impact force on the anchor with a 12 foot free fall on TR was 3.09 kN. Keep in mind, I pulled out a fair amount of slack before I let go and my belayer gave me an intentionally hard catch. So your average TR fall will likely produce less of an impact force on the anchor, unless you weight a lot more than me.

Can you measure the force exerted by the climbers fist on the belayers face after a 20ft toprope fall?

Skurdey

FF=0 is equal to static loading.

As a matter of fact, if one examines the Force vs time over longer period, the one with force oscillation, observation that the loading settles around 300lb is quite obvious, with swings to above ~325 and below 250. Why 300lb, and not 320lb?

Adding rope over the couple of carabiners friction doesn't change the final static loading on the anchor . . .

Hope this helps

FF=0 is equal to static loading.
It is a bit easier to understand this if there is no friction on the system.

Climber rope pulls down with M*g
Belayer rope pulls down with M*g - remember, no frictional losses. Why are these two forces equal? If they were not equal, according to Newton's Laws, something would have to be moving, and we are talking about a static load.

Climber rope pulls down with M*g, belayer rope pulls down with M*g, anchor pulls up with 2*M*g. Why 2*M*g - nothing is moving, forces have to be cancel out, two M*g down, the one going up must be equal to the sum.

As a matter of fact, if one examines the Force vs time over longer period, the one with force oscillation, observation that the loading settles around 300lb is quite obvious, with swings to above ~325 and below 250. Why 300lb, and not 320lb? - possible explanations - additional friction somewhere, i.e. climber touching something, rope rubbing against the rock, instrument not calibrated/erroneous. BTW, I am not implying calibration or erroneous reading issues, the possibility is just listed

Adding rope over the couple of carabiners friction doesn't change the final static loading on the anchor, but the forces get too complicated for the verbal analysis

Hope this helps

...Hooke's Law predicts that the maximum impact force on the climber will be two times his weight.

Why do climbing engineers have hunched shoulders, and sloping foreheads?

When you ask one to describe the real forces on a TR anchor, he'll hunch his shoulders and say "I don't know".

When you show him USN's experiment, he'll slap his forehead and say "I knew it!"

Good lord. There isn't a single post is this thread that is completely accurate, except perhaps the OP, and the one linking to rgold. I don't know where to start.

Hanging without bouncing on toprope, the force on the ANCHOR is the sum of the weight of the belayer, the climber, the rope and if you want to be really picky, the masterpoint biner(s). There is no friction, rope elongation, pulley effect, nothing else to consider. If the climber or belayer is touching the rock or ground, the force will be less.

aargh, you folks scare me.

Good lord. There isn't a single post is this thread that is completely accurate, except perhaps the OP, and the one linking to rgold. I don't know where to start.

Hanging without bouncing on toprope, the force on the ANCHOR is the sum of the weight of the belayer, the climber, the rope and if you want to be really picky, the masterpoint biner(s). There is no friction, rope elongation, pulley effect, nothing else to consider.

aargh, you folks scare me.

I find it a bit hard to believe there isn't decent pro to be had below or to the left of both these bolts.

I'm just curious - why would you want to embarrass yourself by putting this in print?

Good lord. There isn't a single post is this thread that is completely accurate,

Hanging without bouncing on toprope, the force on the ANCHOR is the sum of the weight of the belayer, the climber, the rope and if you want to be really picky, the masterpoint biner(s).

No, it isn't. A fall factor of 0 is a fall. It occurs when you fall on a rope with no slack and no initial tension—for example, an idealized top rope fall. Hooke's Law predicts that the maximum impact force on the climber will be two times his weight.


Jay

Sure about that?