Field Analysis: How Much Force Does a Top Rope Fall Produce?

Search
Go

Discussion Topic

Return to Forum List
This thread has been locked
Messages 1 - 20 of total 42 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
20_kN

Sport climber
20 kN Land
Topic Author's Original Post - Aug 23, 2015 - 08:03pm PT
Background

Earlier this week Rock and Ice published an article involving forces in a TR fall (1). They claimed they were able to reach forces as high as 7kN in their analysis. I did some testing on TR falls a few years back (2), but lieu of the article, I decided to revisit the topic once more.

Setup and Testing Procedures
The objective in this test is quite simple—determine how much force a typical TR fall produces under typical conditions. I conducted three series of tests:

(1) 160 lbs climber takes three TR falls w/ 180 lbs belayer; no twists in the rope at the anchor.

(2) Same as series one, but with two twists in the rope at the anchor.

(3) 180 lbs climber takes three TR falls w/ 160 lbs belayer; no twists in the rope at the anchor.

All three series of tests have the following common properties:

 The route was a 5.10c sport climb with five bolts, it was approximately 45’ tall and it was dead-vertical.

 Each of the three series incorporated three falls—one about 1/4th of the way up the route, the next ½ the way up, and the last at about ¾ of the way up.

 The belayer used a locking belay device; the belayer was not anchored to anything; the belayer did not jump or pull in slack mid-fall to manipulate the catch style.

 The load cell was placed on the anchor so as to measure the peak force on the anchor.

 The rope used was a Maxim Pinnacle 9.5mm, which has the highest impact force rating of any dynamic rope on the market (10.3kN, 31% dynamic elongation, 5% static elongation). This simulates a worst-case scenario with regard to rope choice, unless the climber is TRing on static rope.

 The belayer always maintained 0.5 – 2 feet of slack in the rope. Never was the climber weighting the rope, nor was there a loop of slack hanging down at the belayer or climber.

Setup Photo

Equipment
Measurements were taken with a 3000lbf load cell with a conditioner scanning at 520 Hz. The load cell was properly calibrated, and its accuracy was verified against three other load cells.
Results

Series One – 160 lbs climber, 180 lbs belayer, no twists in rope at anchor
 Fall 1 - 525.7 lbf / 2.33 kN
 Fall 2 - 515.6 lbf / 2.29 kN
 Fall 3 - 465 lbf / 2.07 kN

Series Two—160 lbs climber, 180 lbs belayer, two twists in rope at anchor
 Fall 1 - 462.8 lbf / 2.06 kN
 Fall 2 - 421.6 lbf / 1.88 kN
 Fall 3 - 426.8 lbf / 1.90 kN

Series Three—180 lbs climber, 160 lbs belayer, no twists in rope at anchor
 Fall 1 - 555.6 lbf / 2.47 kN
 Fall 2 - 570.3 lbf / 2.54 kN
 Fall 3 - 600.1 lbf / 2.67 kN

In the spirit of trying to replicate the results R&I got, both my partner and I climbed to the top of the route, pulled out two huge handfuls of slack (about 6-7’), and jumped off to simulate an inattentive belayer. The results were:

160 lbs climber, 180 lbs belayer - 766.3 lbf / 3.41 kN
180 lbs climber, 160 lbs belayer - 728.7 lbf / 3.24 kN

For fun, here is a graph showing the 766.3 lbf / 3.41 mentioned immediately above:


While I do not have a video of series one and two, I have a video of series three:

https://youtu.be/f_hRE9isHx4

Summary
Out of nine falls, six by a 160 lbs climber and three by a 180 lbs climber, the average impact force presented to the top anchor was 522 lbf / 2.32 kN. The maximum impact force presented in any of the nine falls analogous of a typical TR setup with an attentive belayer was 600 lbf / 2.67 kN with the 180 lbs climber and 526 lbf / 2.33 kN with the 160 lbs climber.

When the test was expanded to include TR falls with free-fall drops simulating a large amount of slack in the rope, the maximum impact force I recorded was still only 766 lbf with the 160 lbs climber and 729 lbf with the 180 lbs climber. Also, keep in mind this entire test set was done with the single hardest-catching dynamic rope currently manufactured.

Reference
(1) http://www.rockandice.com/lates-news/Climb-Safe-top-roping-is-not-so-safe?page=2

(2) https://www.mountainproject.com/v/top-rope-fall-analysis-w-strain-gauge-analyzer/107510973#a_107512177
donini

Trad climber
Ouray, Colorado
Aug 23, 2015 - 08:10pm PT
Not enough to break a rope.
Big Mike

Trad climber
BC
Aug 23, 2015 - 08:13pm PT
(We used a belay device clipped directly to a belay bolt—certainly not a recommended use of the device nor a good belay style because it doesn’t allow for dynamic load absorption, but one that allowed us to remove most of the variables from the belay setup.)

This is how they got such large forces. A static belay was used.
apogee

climber
Technically expert, safe belayer, can lead if easy
Aug 23, 2015 - 08:44pm PT
"Not enough to break a rope."

But enough to make lots of people click on the link!
rlf

Trad climber
Josh, CA
Aug 23, 2015 - 08:45pm PT
Only as much as your belayer allows...
the Fet

climber
Tu-Tok-A-Nu-La
Aug 23, 2015 - 08:47pm PT
Thanks for sharing this. Interesting, useful, info.
Spider Savage

Mountain climber
The shaggy fringe of Los Angeles
Aug 23, 2015 - 08:54pm PT
Good to know. Thanks for the work.

20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 23, 2015 - 11:32pm PT
Now if only I can get ahold of R&I to hear their side of the story...
Big Mike

Trad climber
BC
Aug 23, 2015 - 11:39pm PT
^^^^

Read the article. I picked out the quote above.

The belay device was clipped to a bolt.
Dingus McGee

Social climber
Where Safety trumps Leaving No Trace
Aug 24, 2015 - 04:18am PT
The load cell was properly calibrated, and its accuracy was verified against three other load cells.

How does one properly calibrate a load cell for dynamic loading?
fear

Ice climber
hartford, ct
Aug 24, 2015 - 06:35am PT
Not that I'm much of a safety freak but wouldn't it be a good idea to back up that load cell in the anchor with another, loose, QD/sling?

Nice test btw...

Be interesting to see a "static" line test as well.
phylp

Trad climber
Upland, CA
Aug 24, 2015 - 08:21am PT
Very nicely done! Thanks for the report.
CCT

Trad climber
Aug 24, 2015 - 12:04pm PT
Good to think about when using a "guide-style" anchor while belaying a second up to your belay spot. That would be pretty similar to belaying off a bolt, no?

darkmagus

Mountain climber
San Diego, CA
Aug 24, 2015 - 12:07pm PT
Super cool. Thanks for posting!
JimT

climber
Munich
Aug 24, 2015 - 12:26pm PT
Not that I'm much of a safety freak but wouldn't it be a good idea to back up that load cell in the anchor with another, loose, QD/sling?

A 3000lb load cell will have a safe overload of 250% so 7500lbs and the actual breaking strength is way beyond that, typically 8 tons or whatever the eyes are rated at. They are certified for use in lifting applications like cranes.
High Fructose Corn Spirit

Gym climber
Aug 24, 2015 - 12:36pm PT
Interesting: this load cell.

Never heard the term before.

Years ago, as an adventure sport engineering type, used a rented mechanical dynamometer over the course of a week's time to research / test the breaking strands of some climbing rope.

Interesting that the load cell appears to have very fast measuring abilities, to test shock wave frequencies, etc. as fast as ms under load.

How does this work? Are these electronic? Were I to research, what brand should I check out (go-to source?) or are they so generic they are everywhere and I've just been out of the loop here?

Tfpu. Cool research.

(I suppose later today I could just google "load cell" eh? lol)
i'm gumby dammit

Sport climber
da ow
Aug 24, 2015 - 12:59pm PT
Good to think about when using a "guide-style" anchor while belaying a second up to your belay spot. That would be pretty similar to belaying off a bolt, no?
Wouldn't the anchor have a cordellette or other dynamic rope involved?
Banquo

climber
Amerricka
Aug 24, 2015 - 01:38pm PT
Most load cells work with multiple resistance type strain gauges wired in a Wheatstone bridge. The load cell is basically inert with no moving parts and has response time related to how fast electrons go and shock waves move through steel. The instrumentation is where the variables of interest lie. The signal conditioner supplies a regulated voltage (AC or DC types available) to the load cell. The signal conditioner also amplifies the low voltage (a few millivolts) signal coming back from the load cell, varying this amplification (think op amps) is how it is calibrated. The output from both the load cell and the signal conditioner is a voltage in proportion to the force. Signal conditioners have inherent frequency response characteristics and may have analog filters built in to remove high frequency noise. For example, 60 Hz noise is common and undesirable if the shielding of the wires and strain gauges isn't adequate.

It would be of interest to know what electronics were used but it doesn't much matter because the impulse being measured is a very low frequency - looks like about 2 Hertz from the plot. Above 5 or 10 Hz there isn't anything of interest in this type of test so most any signal conditioner will do. The human body probably doesn't respond to frequencies much above that and it is unusual to find signal conditioners with low pass filters below 2 Hertz. Above 10 Hz, long term exposure might be an issue with things like nerve damage from using a palm sander (often 60 Hz). Good signal conditioners without filters usually work well up to about 10 kHz.

If my memory is any good (no), I think the natural frequency of a person sitting down is around 10 Hz which is a problem in vehicles and aircraft because people respond to the vibration and it becomes hard to see. Maybe that has more to do with the response frequency of the muscles controlling the eyes and/or head. I forget.

Listen to this frequency generator to get an idea of what 10 Hz to 10 kHz is:
http://onlinetonegenerator.com/
If you have good speakers, you can feel 10 Hz.

The second most common type of load cell is piezoelectric. These are used for dynamic forces only and cannot measure static forces. Used for impact measurement. If you were investigating the force applied to a piton by a hammer a piezoelectric load cell would be the way to go.

There are other types of load cells but they are not common.

electric resistance strain gauges:
http://danquo.blogspot.com/2012/02/strain-gages-and-strain-gauges-of.html

PS:
If the signal conditioner used has a built in low pass 2 Hz filter, the data in the plot is junk.
'Pass the Pitons' Pete

Big Wall climber
like Ontario, Canada, eh?
Aug 24, 2015 - 01:39pm PT
Would like to see this done with static rope, too! [minus any intentional slack]
CCT

Trad climber
Aug 24, 2015 - 01:45pm PT
Wouldn't the anchor have a cordellette or other dynamic rope involved?

Not necessarily. A lot of people build anchors out of nylon or dyneema slings. I don't know how well dyneema can absorb impulse forces, but I thought it wasn't very good.
Messages 1 - 20 of total 42 in this topic << First  |  < Previous  |  Show All  |  Next >  |  Last >>
Return to Forum List
 
Our Guidebooks
Check 'em out!
SuperTopo Guidebooks


Try a free sample topo!

 
SuperTopo Videos

Recent Route Beta