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?

Sure about that?

*facepalm*

Pretty sure. We're talking plain vanilla Hooke's Law. No dampening.

Jay

For the climber at the instant he came to rest, the force would be:

-kx = mg

How do you get 2xthe climbers (I assume you meant mass?) "weight" out of that?

Were you thinking about the load the anchor would see? I could understand that, I think.

I don't know about Jay, but I am, FF = distance of fall (before the rope starts to catch you)/amount of rope (before the rope starts to stretch), so if there is 0 slack, and 0 tension, and a full 200 ft of rope out, the FF will be 0/200 = 0, but the rope will certainly stretch quite a bit before you come to a stop.

For the climber at the instant he came to rest, the force would be:

-kx = mg

Nor where to stop, unfortunately for you.


No friction? I think you need to think that through a little more.


Is that your best pirate voice? At least it's better than your physics.

Jay

It's easy enough to calculate. If the climber falls a distance x the potential energy is mgx. This has to equal the potential energy of the rope which is 1/2*k*x^2. Solve for x and you have x=2mg/k. So, F=kx=2mg.

The three figure shows the peak at about 40, 22, and 11, respectively. Can you clarify what the units of the horizontal axes are in each of the figures, and explain why peak occurs at different values?

Jay

In the future, like Jay points out, your figures need a bit of work. Label all axes for each figure - that little bit of time spent helps to strengthen all of the time spent previously generating data to populate the figures.

I'm curious about consistency, though. Have you tried taking the same fall with the same style catch multiple times and plotting the results? I wonder what kind of variance you might find.

Next time you run some tests, could you measure the peak load from a fall factor=zero fall on a top rope?
Thanks. I look forward to further test results.

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 hope that wasn't all you got, because you need something left for skurdeykat.

Jay

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.

Very happy people like you enjoy this stuff, it means I will never have to. Instead, I can spend all those hours climbing.

Eman

Ironically, though Widgeteers are well-versed in the intricacies of load distribution, impact force, and lobe geometry, they rarely have as keen a grasp of the physiological techniques of climbing itself.

Those units were chosen for me by Excel and I cant figure out how to change them. Anyway, they are row numbers. Because the strain gauge conditioner software creates a new row every 10mS, those units also represent time. Specifically, they are the duration multiplied by ten. So if you are looking at the waveform and notice a particular point starts out at say 30 and ends at say 60, that means it covered 300mS total. The reason why the peaks are at different intervals is because Excel uses the starting row number from the dataset I selected as one, not the start of the entire dataset. The entire dataset has over 150,000 points, so scroll through the data to the dataset that’s relevant to the fall I want to view, and I graph just the points I want. So for example, the data I want may land in rows 120,000 – 121,000. So when I chart out the rows in 120k - 121k, the graph shows 1 - 1,000 instead of 120k-121k because I only selected 1,000 rows. This is an example of the dataset that exists in the .csv file generated by my strain gauge conditioner software:

730321 347.9256
730331 350.5929
730341 355.9004
730351 365.2213
730361 374.1467
730371 377.9456
730381 380.442
730391 383.4596
730401 388.9277
730411 394.7827
730421 401.5505
730431 407.5202
730441 414.8244
730451 422.0302
730461 425.8789
730471 428.9844
730481 433.2427
730491 434.0447
730501 438.4572

The number on the left indicate the time stamp, in mS, generated by the strain gauge software. The numbers on the right are the readings, in lbs. The rows are not listed above. What I am trying to get Excel to do is list the time stamps on the X axis and the load values on the Y axis, but I cant figure out how to get Excel to do this. It wont let me change the X axis values, it forces me to use the row numbers.

[T]he FA just wanted to make a playground for the kids to play on, sorta speak.

Yes. I'll never understand the obession with gear, though if you're into it, more power to you. I'm just thinking of this line, however, in an article that's been going around about different climbing types, in which it describes the "Widgeteer":

Ironically, though Widgeteers are well-versed in the intricacies of load distribution, impact force, and lobe geometry, they rarely have as keen a grasp of the physiological techniques of climbing itself.

Does anybody know how to air-pop popcorn?

I can do that, as long as it doesn't involve math or excel spreadsheets.

Josh

I am amazed this was made a sticky. Really, is RC.com getting desperate. Really should let this get buried before people think the OP actually knows what his doing and talking about.

good work commando,( assuming you really did this yourself and did not fool someone else to do it for you). next time you are in the valley, stop by and I'll get you a free coffee at the lodge.

what brand was the load cell and the receiver ( does it offer serial or USB output )?