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

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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.
WBraun

climber
Aug 24, 2015 - 01:54pm PT
We have one of these bad boy portable Bluetooth beauties.


https://www.rockexotica.com/product/enforcer/
NutAgain!

Trad climber
South Pasadena, CA
Aug 24, 2015 - 02:01pm PT
Two days ago I was at the top of a pitch with a tied dyneema powerpoint between two bolts, and ATC in guide mode belaying up my follower. I did actually have a backup to that so the dyneema sling wouldn't be a single point of failure...

So what's the cliff notes version here?

Belaying at the top with ATC guide means no pulley effect doubling the force on the anchor. Is the force of a follower fall enough to jeopardize a tied dyneema sling?

Seems like it would be a bad idea to let the follower lead through and factor-2 before placing anything else- at least rig up the belay back off the harness for a more dynamic catch....


It would be good for the top rope tests to simulate real conditions with rope drag or inattentive belayer where there is a loop of slack out.

High Fructose Corn Spirit

Gym climber
Aug 24, 2015 - 03:41pm PT
Banquo, thanks for those details. It's all very interesting.

Werner, can I have it? :)



So say we moved away from (a) dynamic climbing rope and climber and belayer to (b) a ten foot static truckers rope and ten pound weightlifter's weight and dropped the weight from anchor with this load cell in place. Would this be too much for it in any regard? Apparently not in load as Werner's load cell load max is 20kn but how about speed / shock values? In above example OP's max load takes place on the order of half second. Max load in weight drop on trucker's rope is likely tenth second (100ms) or faster. Could it handle this speed? How about a 10lb drop on a steel wire where speed /shock might be 10ms at very high lbf value?

Will check into it more later.

Could it handle this speed?

I mean in regard to accurate measurement, graph data, on the order of milliseconds... 2ms, 20ms, 200ms, etc..
rgold

Trad climber
Poughkeepsie, NY
Aug 24, 2015 - 03:51pm PT
Banquo, care to speculate about how R&I did a very similar test (fall factors are 0.11 and 0.14) and got nearly double the readings? I don't think offhand that much increase is explained by having the belay device on a bolt rather than a human and by having a 200 lb faller rather than a 180 lb faller.
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 24, 2015 - 04:04pm 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?
//

When belaying directly off the anchor you do not have a a 2:1 pulley like you do when top roping, which unless there is a bunch of slack in the system or the climber is near the anchor, means the loads should be even lower when belaying right off the anchor on a multipitch climb.

//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.//


IT was backed up with a 4' sling, I just removed the sling to take the photo. Anyway, load cells are designed for overhead lifting and the one I was using was stronger than the biners attached to it.
CCT

Trad climber
Aug 24, 2015 - 04:21pm PT
When belaying directly off the anchor you do not have a a 2:1 pulley like you do when top roping, which unless there is a bunch of slack in the system or the climber is near the anchor, means the loads should be even lower when belaying right off the anchor on a multipitch climb.

Thanks for the info, 20_kN! Really great discussion here. Since it's not a pulley, does that mean that the maximum force would be closer to 3.5kN (ie half of 7kN)?

Also, does this have any bearing on the common practice of clipping the top-most piece in the anchor as a first piece of pro as the leader takes off? My understanding is that people do this to protect the belayer. I'm thinking that getting jerked towards the anchor with 7kN could be damaging too, or even rip the piece out (small cam, marginal placement).

20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 24, 2015 - 04:23pm PT
Banquo, thanks for those details. It's all very interesting.

Werner, can I have it? :)



So say we moved away from (a) dynamic climbing rope and climber and belayer to (b) a ten foot static truckers rope and ten pound weightlifter's weight and dropped the weight from anchor with this load cell in place. Would this be too much for it in any regard? Apparently not in load as Werner's load cell load max is 20kn but how about speed / shock values? In above example OP's max load takes place on the order of half second. Max load in weight drop on trucker's rope is likely tenth second (100ms) or faster. Could it handle this speed? How about a 10lb drop on a steel wire where speed /shock might be 10ms at very high lbf value?

Will check into it more later.

I have conducted static drop tests in a number of different types of material: dyneema, nylon, via ferrata lanyards, steel cable, and other items. In addition, this thread I created talks quite a bit about sample rates and load cells as well:

http://www.mountainproject.com/v/quick-study-involving-falls-on-static-materials/108262937

In short, it depends on your load cell and signal conditioner. Even cheap load cells can effectively respond down to about 0.5mS. Below that you'll need a better one. However, the limiting factor is usually the conditioner. In my case, 520Hz. is as fast as I can go. The Rock Exotica Enforcer pictured above can do 1,500Hz. but it can only log at 500Hz. I found 520Hz. to be more than fast enough to measure anything climbing related except drop tests on very static material, but even then I can still get fairly close. Further, it's easy to determine if the sample rate was fast enough or not once I look at the data.

Here is a test in which I compared 10Hz. vs 520Hz. on a dynamic load on the same event. You can see the results are not that different, although there is a bit of a difference.


Here is an example in which the sample rate was not quite fast enough:

High Fructose Corn Spirit

Gym climber
Aug 24, 2015 - 05:16pm PT
Thanks 20kn, I'll be checking it out.

a "gibbon butt bounce," hmmm :)
Banquo

climber
Amerricka
Aug 24, 2015 - 05:50pm PT
Banquo, care to speculate about how R&I did a very similar test (fall factors are 0.11 and 0.14) and got nearly double the readings?

Different ropes will have different stiffness, even lead ropes. A fat rope might be stiffer than a skinny. Also, isn't 20_kN's test a fall factor 1 while the R&I sounds like it is close to 2? Lifting the belayer will certainly reduce the force. However, the lower load readings could be in part due to filtering in the instrument. If it was designed for static weighing, it might be heavily filtered. Many scales have filtering because if the truck or whatever you are weighing is bouncing or something you want to filter that out. I have a cheap platform scale in the garage that is very accurate weighing boxes but cannot weigh me no matter how still I try to stand - it probably doesn't have filtering.

Werner's tool is very cool with bluetooth and all but I tried to look up the specs and couldn't find anything about frequency response. It seems to have two sample rates which is different. Since it is purpose specific, it probably has high enough frequency response but I'd want to know before I bought one. I guess I wouldn't buy one anyway since I have a box of load cells in the garage already.

I have some signal conditioners in the garage (CALEX Model 162MK Bridgesensor) that you can vary the cutoff filter from 10Hz to 1000Hz by changing dip switch settings. I always want specifics on filtering if something dynamic is being measured. I usually filter less, sample faster and then filter the resulting data by smoothing or FFT. I like to sample at least 4x the maximum frequency I am interested in. Low sample rates without filtering results in aliasing and your data is junk. Best solution is to filter to some reasonable frequency and sample 4x that frequency. So, for a climbing rope drop test I might analog filter to 100Hz and sample at 400 Hz.

If the signal conditioner gives flat response to 520Hz, it is plenty fast enough. I'd still be interested in manufacturer and model number for the equipment. Just because it samples at 500Hz doesn't mean there isn't filtering to something lower. Calibration is probably right because the static load at the end of the test appears to be the combined weight of the climber and belayer.
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 24, 2015 - 06:08pm PT
However, the lower load readings could be in part due to filtering in the instrument.

Werner's tool is very cool with bluetooth and all but I tried to look up the specs and couldn't find anything about frequency response. It seems to have two sample rates which is different. Since it is purpose specific, it probably has high enough frequency response but I'd want to know before I bought one. I guess I wouldn't buy one anyway since I have a box of load cells in the garage already.

I have some signal conditioners in the garage (CALEX Model 162MK Bridgesensor) that you can vary the cutoff filter from 10Hz to 1000Hz by changing dip switch settings. I always want specifics on filtering if something dynamic is being measured. I usually filter less, sample faster and then filter the resulting data by smoothing or FFT. I like to sample at least 4x the maximum frequency I am interested in. Low sample rates without filtering results in aliasing and your data is junk. Best solution is to filter to some reasonable frequency and sample 4x that frequency. So, for a climbing rope drop test I might analog filter to 100Hz and sample at 400 Hz.

If the signal conditioner gives flat response to 520Hz, it is plenty fast enough. I'd still be interested in manufacturer and model number for the equipment. Just because it samples at 500Hz doesn't mean there isn't filtering to something lower. Calibration is probably right because the static load at the end of the test appears to be the combined weight of the climber and belayer.

There is no filtering enabled. I always keep filtering disabled. I am not using some crane scale or truck scale of sorts. I am using a conditioner designed for R&D analysis.

The conditioner is VERY user programmable. You can write your own filter, choosing cut-off frequencies, a range of freqs, or specific freqs, and you can set the steps per division filtering level as well, or in my case completely disable it. You can also set dynamic filtering where you write a custom filter to suit your needs, and have the device momentarily disable filtering if the load spiked above a value of your choosing over a duration of your choosing (e.g. to measure a dynamic load when measuring something that is normally static). I always keep filtering disabled because the resolution of the conditioner is good enough that even at 500 Hz. the readings are still quite stable thus rendering the filtering quite unnecessary unless I am going to try to weigh a 100 lb object with a 50,000 lb load cell or something silly like that.

The unit also allows for temperature calibration linearization, sensitivity linearization across 8 steps/ readings, as well as a number of other linearization features if you want to use them.

If you want a conditioner with a TON of features and a ton of user customization for a reasonable price, it’s a great option. The drawback is because it’s so customizable, it’s not that user friendly if you do not understand how signal conditioners work, and you need a very basic understanding of how command prompts work in Hyper Terminal or Putty if you want to unlock the most advanced features. But for those who want all the advanced features and are willing to put in the work to learn, this conditioner is a great buy for the money.


This is the conditioner if you want to look it over: http://www.mantracourt.com/products/signal-converters/usb-load-cell-converter

As far as the sample rate of the Enforcer, it runs at 1500 Hz. if put on peak hold or 500 Hz when logging. So if you want to log you're limited to 500Hz. The Enforcer is a good option for something simple and compact that you can take in the field, but if you are "really" into test and analysis, my conditioner offers far more features at the cost of being less compact and requiring a laptop to run.
Banquo

climber
Amerricka
Aug 24, 2015 - 06:59pm PT
That's a cool signal conditioner. Things sure have changed in instrumentation during the past 35 years. I'm an Analog type guy so I don't know much about recursive filters and should probably study up. When I google recursive filter and look at images, I see some interesting data plots. But, if you have left the filter inactive, it probably isn't a factor.

Anyway, I'm not dissing what you've done since I doubt there is anything happening above 2 Hz which is pretty much static in the instrumentation world. Two sacks of meat hanging on the ends of an elastic rope are not going to be a high frequency system. Your results seem entirely reasonable to me.

Out of idle curiosity I'd be interested in what data your system produces for a high frequency impact. It would be fun to see what you get with a hammer and funkness device or something like that. Even more fun to see what the recursive filter does to it. I know I can generate 10 kips with a hammer on a solid surface. No need to do this, it's just what I'd do if I was goofing off.

Like I think you are, I am suspicious of the R&I data and we know nothing about their equipment. I don't read or get R&I so don't really know what the article says. The last issue on my shelf after I dropped my subscription is November 2002.
Paul Martzen

Trad climber
Fresno
Aug 24, 2015 - 07:09pm PT
Nice report.

Would be interesting to see the results of a direct replication. Attaching the belay device directly to a static bolt. Seems odd that the forces would jump from 2 KN all the way to 10 KN.
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 24, 2015 - 07:10pm PT
That's a cool signal conditioner. Things sure have changed in instrumentation during the past 35 years. I'm an Analog type guy so I don't know much about recursive filters and should probably study up. When I google recursive filter and look at images, I see some interesting data plots. But, if you have left the filter inactive, it probably isn't a factor.

Anyway, I'm not dissing what you've done since I doubt there is anything happening above 2 Hz which is pretty much static in the instrumentation world. Two sacks of meat hanging on the ends of an elastic rope are not going to be a high frequency system. Your results seem entirely reasonable to me.

Out of idle curiosity I'd be interested in what data your system produces for a high frequency impact. It would be fun to see what you get with a hammer and funkness device or something like that. Even more fun to see what the recursive filter does to it. I know I can generate 10 kips with a hammer on a solid surface. No need to do this, it's just what I'd do if I was goofing off.

Like I think you are, I am suspicious of the R&I data and we know nothing about their equipment. I don't read or get R&I so don't really know what the article says. The last issue on my shelf after I dropped my subscription is November 2002.

I included a link to a copy of the article in my study under the reference section. The conditioner is not fast enough to measure the peak force of a funkiness device. You would probably want a minimum of 3,000Hz. for something like that, although 10,000 would be better.
mikllaw-Oz

Sport climber
tempe Australia
Aug 24, 2015 - 09:04pm PT
Backing up (but not guaranteeing) the accuracy of this is the fact that the graph showing the 766.3 lbf / 3.41 kN goes to 340 lbs at the end, which is the combined weight of the 160 and 180 lb climbers.

rgold

Trad climber
Poughkeepsie, NY
Aug 24, 2015 - 10:18pm PT
Different ropes will have different stiffness, even lead ropes. A fat rope might be stiffer than a skinny.

Yes, but 20 kN was using one of the stiffest dynamic ropes around.

Also, isn't 20_kN's test a fall factor 1 while the R&I sounds like it is close to 2?


OMG no---they were using real people! According to 20 kN's numbers, his falls had fall factors about 0.13, whereas the R&I fall factor was about 0.10. So 20kN's climbers were a bit lighter than the R&I guy, but not enough to halve the maximum tension!

Lifting the belayer will certainly reduce the force. However, the lower load readings could be in part due to filtering in the instrument.

Yes for lifting. But 20 kN had no filtering implemented for the tests.

So it remains mysterious: a slightly heavier faller with a slightly smaller fall factor and a more static belay nearly doubles the maximum impact force?
i'm gumby dammit

Sport climber
da ow
Aug 25, 2015 - 01:12am PT
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.
You are correct that some do. They shouldn't for exactly the reason you are worried about. I use to to lead solo by clipping longish dyneema slings to bolts or gear and then unclip the low one as i moved up until the error of my ways was pointed out to me. I still had the dynamic absorption of my harness but that may have not been enough. I rarely do it these days (got a girlfriend) but when I do I use 10' segments of dynamic rope double fishermaned into 4' loops with loosely tied figure 8 bights on each end so I get a softer catch from the dynamic rope, harness, and the tightening of the bights. Now I'm slightly less likely to experience the 'yer gonna die' syndrome if i fall.
CCT

Trad climber
Aug 25, 2015 - 09:44am PT
I wonder about a guide belay onto a cam anchor via a dyneema sling (knotted or not).

I also wonder about clipping an anchor piece as the first piece of gear using a dyneema sling in case of an early fall.

These two scenarios are very common, and you don't really hear of accidents related to them. But from the numbers alone, it feels like they can't be very safe.

Anyone understand the physics better than me and can set my worries to rest?
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 25, 2015 - 05:09pm PT
I wonder about a guide belay onto a cam anchor via a dyneema sling (knotted or not).

I also wonder about clipping an anchor piece as the first piece of gear using a dyneema sling in case of an early fall.

When a dynamic rope is in the system, there is little consequence between using a dyneema or nylon sling. The sling is not the primary energy absorbing element, the rope is, and it will have little to no measurable effect in the field. In the case of the second falling on TR with a dyneema-made anchor vs nylon-made, there would be absolutely zero measurable difference. With regard to taking a fall directly into the belay on a dyneema sling vs a nylon, there would also be little difference. BD tested this quite awhile ago and found about a 2-5% lower impact force with a nylon sling vs dyneema.

However, they used a rigid weight, static belay and a drop tower. In the field, with a flexible mass and movable belayer, the differences would drop even more.
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 26, 2015 - 10:33pm PT
http://blackdiamondequipment.com/en/qc-lab-to-screamer-or-not-to-screamer.html
i'm gumby dammit

Sport climber
da ow
Aug 27, 2015 - 01:27am PT
I wonder about a guide belay onto a cam anchor via a dyneema sling (knotted or not).
There is a huge difference between knotted and knot with Dyneema. Watch this video.
http://dmmclimbing.com/knowledge/slings-at-anchors/
As you can see here the dyneema should be ok at 7kN, but I wouldn't be overly comfortable with the margin since the overhand knotted dyneema failed at 10.4 kN in the example. Although a 10kN fall is likely gonna have you pretty messed up even if you don't deck.
20_kN

Sport climber
20 kN Land
Topic Author's Reply - Aug 27, 2015 - 02:10am PT
There is a huge difference between knotted and knot with Dyneema. Watch this video.
http://dmmclimbing.com/knowledge/slings-at-anchors/
As you can see here the dyneema should be ok at 7kN, but I wouldn't be overly comfortable with the margin since the overhand knotted dyneema failed at 10.4 kN in the example. Although a 10kN fall is likely gonna have you pretty messed up even if you don't deck.


While true, it's also worth noting the test used a 2-piece anchor. If you are building a cam nest with an 8' Dyneema sling, you may have more than one run of Dyneema in the mater point, which if you do will increase the strength.

Also worth noting is that they used a rigid mass in a scenario with no dynamic element. Adding a dynamic element (i.e. a human and dynamic rope) would very likely increase the strength of the knotted Dyneema relative to the video's results.

The problem is that Dyneema has a very low melting temperature (about 290F). Dyneema starts to lose strength with exposure to any level of heat, which means the mere fact that the sling was shockloaded so quickly, and not more gradually such as with a dynamic rope, very likely increased the temperature of the Dyneema enough that it affected the strength of the sling.

DSM, the manufacturers of Dyneema, in their own literature, openly claim that SK-75 Dyneema has a 22% strength loss just by the time it hits 140F. In addition, DMM found that frozen Dyneema slings with knots in them were substantially stronger than ones at room temperature for this very reason.

http://dmmclimbing.com/knowledge/knotting-dyneema-vid/

But probably most imporant is DMM's own research. In the same video I just linked DMM did a static pull test of a knotted Dyneema sling and then they did a FF2 drop on it. In the static test, the sling held 18kN. On the FF2 it only held 12kN and it failed.

overwatch

climber
Aug 27, 2015 - 07:55am PT
you guys must be a riot at a party. This forum constantly impresses me with the level of intelligence and caliber of thinking, especially to a door kicker like me. Thanks for the info
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