Is Shock loading a myth?

Forgive the titles, it's a youtube thing.  But for real, extension isn't always a problem.  I see people set up top rope anchors with limiter knots and they have A LOT of dynamic rope in the system.  Also, when we pull on clove or girth master points or limiter knots in dyneema stuff slips.  Anywhere from 2 to 10kn it slips and then it all falls apart.  Quad anchors we have tested (video coming soon) and those are rad but sometimes sliding Xs are super good enough.  Whatcha think!?

The thought process with the X is with a persons  bodyweight on a static tether. 

Rob WardenSpaceLizard wrote: The thought process with the X is with a persons  bodyweight on a static tether. 

If you watch the video he does a drop connected directly to the anchor point with dynos as a static tether 

Really interested in seeing your testing on clove and girth hitch master points.

Done any testing on 60cm runners as a sliding x? Seems the shock loading would be less.

Ben Podborski wrote: Really interested in seeing your testing on clove and girth hitch master points.

Coming very very soon.  Maybe in about a week.

what are your thoughts on pulling a P shaped glue-in in shear, but perpendicular to the P lip so it would torque the bolt against the glue, if that makes sense? i came across somebody on reddit who was convinced this would meaningfully weaken a glue in if you were climbing far off to one side of it. i didn't think it would be produce meaningful forces in a climbing scenario but couldn't find any data to back it up.

Uhhh, the video doesn’t look at shock loading at all. All they did was measure peak impact force at several points of interest. They missed the time over which that force was applied....

You need to look at force vs. time to really understand what could be considered a shock load.

This video should be titled “max forces at various points in rope system”

chris blatchley wrote: what are your thoughts on pulling a P shaped glue-in in shear, but perpendicular to the P lip so it would torque the bolt against the glue, if that makes sense? i came across somebody on reddit who was convinced this would meaningfully weaken a glue in if you were climbing far off to one side of it. i didn't think it would be produce meaningful forces in a climbing scenario but couldn't find any data to back it up.

Yeah, someone on reddit........

curt86iroc wrote: Uhhh, the video doesn’t look at shock loading at all. All they did was measure peak impact force at several points of interest. They missed the time over which that force was applied....

You need to look at force vs. time to really understand what could be considered a shock load.

This video should be titled “max forces at various points in rope system”

The force required to arrest a fall, to first order, is 9.8*M*L/D newtons, where M is the mass of the climber in kilograms, L is the length of the fall and D is the length of stretch in your rope/sling/body, both in meters. To higher order, the peak force is the maximum of some function that needs to integrate over the length of the arrest to the total work done by the fall, 9.8*M*L. This function will in reality be roughly constant - the force will be spread out evenly during the duration of the arrest, assuming the rope and person behave as springs, which they mostly do.

So, yeah, the video is indeed measuring the shock load.

curt86iroc wrote: Uhhh, the video doesn’t look at shock loading at all. All they did was measure peak impact force at several points of interest. They missed the time over which that force was applied....

You need to look at force vs. time to really understand what could be considered a shock load.

This video should be titled “max forces at various points in rope system”

The maximum force is all that is relevant in this case. The speed at which a force is applied IS important to materials scientists and engineers and is called the rate of strain, the strength of materials varies with the rate of strain. Some get stronger as the strain rate increases, some weaker and some do both, there are curves available for most materials. Because polymers usually flow they usually get "stronger" the faster the force is applied and this is the case for nylon 6.6. We are talking about milliseconds though so nothing of interest to us, the researchers stop measuring at rates of over 5000/s.

Interesting Video. Quite a while ago we did some tests for the german alpine club simulating a factor 2 fall with a tire + sand for weight into a sliding X with a failing point (used a 3 mm cord with a single fishermans knot which breaks rather easy).. In our experiments we did measure a quite high peak force due to shock loading. Also more recently the austrian mountain guides did some tests with runners as lanyards and showed, that even "small" static falls into those runners (with and without knots) could generate enogh force to break them ( youtube.com/watch?v=qXN4uxI… ).. IMO this shows that shock loading is a problem we need to be aware of.
And if you think about it: the anchor will most likely not fail while you just sit on it, so to be really realistic you would need to to whip onto the belay to find out..

Even more exciting is when the lead climbet takes a FF2  straight onto the belayer and then the belay fails, the combined effect of the belay force on the leader and the increased force on the belayer as they are accelerated downwards breaks everything. I've done hundreds of drop tests on all the possibilities with sliding anchor systems and there are plenty of interesting scenarios to explore. The sliding X is junk.

I think for short falls like in the video the squishyness of the body is probably not modeled well by a solid weight.  As the fall length get longer the model is more realistic.

This is all covered in a rather nicely cheap book on multipitch climbing. Just one click away on Amazon. The video covers half the truth, and as this can be obtained by logic the testing was a bit pointless (much of their testing videos are great - if only they were shorter). It covered a tool, the sliding X, but didn't put it into a system - a climber being belayed, so like a video on crevasse rescue with no weight on the line, less use than one think. So here goes. 1. One cam blowing and the anchor extending by 60cm is no different to a 60cm fall. All that matters is the amount of rope in the system. If your back and anchor can't take a 60cm fall on 10m of rope, then we would all be worried. 2. I thought he was going to do some FF2 falls when clipped in via a sling. Now that would have been interesting. Maybe I skipped through too quickly? 3. This is an example of why "having the tools in the tool box" is such a shit way of teaching. It is about the systems. So, a sliding X with rope in the system and a clove is just a much better idea than a sliding X and then clipping in with a daisy. This is the only demo that was needed. 4.  There was no belayer!!!!! If there had been, her weight would have also fallen 60cm. So the test they needed to do was a FF 2 i.e. the guy moving above the belay whilst clipped in with a sling or daisy, and the belayer clipped to the power point with a sling or daisy. This might give a FF3 equivalent and 60cm might be important. 5. It needed a discussion of the difference between slacklining and climbing. With slacklining the forces are always massive, with climbing only if someone falls are there forces much above body weight. Hence in slacklining knots I guess become a problem, as undoing them must be a pain. In climbing few of us fall onto the anchor, so an overhand is not really a problem. 6. One bolt just blew. This means there is a higher than normal chance of the second one blowing (same age, same bad glue......), hence minimising force on the remaining bolt a good idea. 7. Extension. Would the chances of the belayer letting go increase if she was dropped 60cm. I would say YES, big time. If you find yourself plummeting off a belay for no reason, you might panic. So again systems count: Guide mode solves this, but only for bringing up the second; a grigri for leading - but uncommon with many climbers on multipitch outside the USA. 8. If they had had the belayer in play, then although the climber is on say 10m of rope, she isn't and takes a FF1 kind of fall. 8. now for the math bit. Why use a sliding X? It is quick. However, it leaves no place for the second to clip into, and don't forget the reverso is in guide mode on the same X, so things are getting crowded and potentially trapped. This is fine on easy ground as the belayer can unwieght and a second locker be slid in, but not on steep stuff. And on easy ground the fall forces are normally small. Various rescue stuff becomes harder too without a powerpoint. Some might argue it helps equalise the forces. But for that to be useful, the following has to be true (if I had a quid for every time I've typed this; Jim was the person who explained it to me): (a) by itself neither piece can hold the forces (or no need to equalise); (b) both pieces can take at least half the force (or one piece will blow). If (a) is not true, an overhand would be as good. If (b) is not true, you would be better off with an overhand, as this offers less extension and hence the belayer might hold the rope, and forces are minimised. This leaves a very narrow window when a sliding X can be of benefit. Because of this, sliding X's have no real advantage (except a very slight speed advantage(5 seconds?) if the second if leading through and you are indirect belaying all the time) and the big downside that the belayer might drop you. If you are worried about not being able to untie the over hand knot if you create a powerpoint, use an butterfly, fig9 or tiger clip.

David Coley wrote:
This is all covered in a rather nicely cheap book on multipitch climbing. Just one click away on Amazon. The video covers half the truth, and as this can be obtained by logic the testing was a bit pointless (much of their testing videos are great - if only they were shorter). It covered a tool, the sliding X, but didn't put it into a system - a climber being belayed, so like a video on crevasse rescue with no weight on the line, less use than one think. So here goes. 1. One cam blowing and the anchor extending by 60cm is no different to a 60cm fall. All that matters is the amount of rope in the system. If your back and anchor can't take a 60cm fall on 10m of rope, then we would all be worried. 2. I thought he was going to do some FF2 falls when clipped in via a sling. Now that would have been interesting. Maybe I skipped through too quickly? 3. This is an example of why "having the tools in the tool box" is such a shit way of teaching. It is about the systems. So, a sliding X with rope in the system and a clove is just a much better idea than a sliding X and then clipping in with a daisy. This is the only demo that was needed. 4.  There was no belayer!!!!! If there had been, her weight would have also fallen 60cm. So the test they needed to do was a FF 2 i.e. the guy moving above the belay whilst clipped in with a sling or daisy, and the belayer clipped to the power point with a sling or daisy. This might give a FF3 equivalent and 60cm might be important. 5. It needed a discussion of the difference between slacklining and climbing. With slacklining the forces are always massive, with climbing only if someone falls are there forces much above body weight. Hence in slacklining knots I guess become a problem, as undoing them must be a pain. In climbing few of us fall onto the anchor, so an overhand is not really a problem. 6. One bolt just blew. This means there is a higher than normal chance of the second one blowing (same age, same bad glue......), hence minimising force on the remaining bolt a good idea. 7. Extension. Would the chances of the belayer letting go increase if she was dropped 60cm. I would say YES, big time. If you find yourself plummeting off a belay for no reason, you might panic. So again systems count: Guide mode solves this, but only for bringing up the second; a grigri for leading - but uncommon with many climbers on multipitch outside the USA. 8. If they had had the belayer in play, then although the climber is on say 10m of rope, she isn't and takes a FF1 kind of fall. 8. now for the math bit. Why use a sliding X? It is quick. However, it leaves no place for the second to clip into, and don't forget the reverso is in guide mode on the same X, so things are getting crowded and potentially trapped. This is fine on easy ground as the belayer can unwieght and a second locker be slid in, but not on steep stuff. And on easy ground the fall forces are normally small. Various rescue stuff becomes harder too without a powerpoint. Some might argue it helps equalise the forces. But for that to be useful, the following has to be true (if I had a quid for every time I've typed this; Jim was the person who explained it to me): (a) by itself neither piece can hold the forces (or no need to equalise); (b) both pieces can take at least half the force (or one piece will blow). If (a) is not true, an overhand would be as good. If (b) is not true, you would be better off with an overhand, as this offers less extension and hence the belayer might hold the rope, and forces are minimised. This leaves a very narrow window when a sliding X can be of benefit. Because of this, sliding X's have no real advantage (except a very slight speed advantage(5 seconds?) if the second if leading through and you are indirect belaying all the time) and the big downside that the belayer might drop you. If you are worried about not being able to untie the over hand knot if you create a powerpoint, use an butterfly, fig9 or tiger clip.

I think you misunderstood the video.  He was basically simulating a belayer clipped into the anchor with a static PAS and one anchor piece blowing.  This is a realistic scenario for rapping a route.  No rope was in the system and yet the forces on the remaining piece were always fairly moderate; not nearly the forces generally thought to occur by the shock loading crowd.

EDIT:  Sorry, I am suffering from a corona virus induced grumpiness.   You are right, the rope is the dominating factor in most of the test.  The last series where Ryan had the load cell connected to his harness then to the sling without a rope are the only tests I was really interested in and forgot about the rest as they were pretty much what I expected.   

If Ryan could stop talking so much it might be easier to watch.

climber pat wrote:

I think you misunderstood the video.  He was basically simulating a belayer clipped into the anchor with a static PAS and one anchor piece blowing.  This is a realistic scenario for rapping a route.  No rope was in the system and yet the forces on the remaining piece were always fairly moderate; not nearly the forces generally thought to occur by the shock loading crowd.

Or you are misunderstanding something! If one of your pieces blows at half bodyweight and the other is capable of holding the 2.8kN (or whatever it was) the sliding was doing nothing anyway EXCEPT increasing the force on the remaining piece, an overhand or whatever is safer.

Jim Titt wrote:

Or you are misunderstanding something! If one of your pieces blows at half bodyweight and the other is capable of holding the 2.8kN (or whatever it was) the sliding was doing nothing anyway EXCEPT increasing the force on the remaining piece, an overhand or whatever is safer.

I remember a statement of yours along the lines that climbers should place good pieces and connect them together to create a anchor.    I believe the all is lost if your pieces are crap in the first place.  In my opinion a 2.8 kN placement is a crap piece for an anchor piece.  I also agree that limiting extension is a good idea.

Hson P wrote:

The force required to arrest a fall, to first order, is 9.8*M*L/D newtons, where M is the mass of the climber in kilograms, L is the length of the fall and D is the length of stretch in your rope/sling/body, both in meters. To higher order, the peak force is the maximum of some function that needs to integrate over the length of the arrest to the total work done by the fall, 9.8*M*L. This function will in reality be roughly constant - the force will be spread out evenly during the duration of the arrest, assuming the rope and person behave as springs, which they mostly do.

So, yeah, the video is indeed measuring the shock load.

the force required to arrest a fall and a shock load are not the same thing. a shock load is defined as an impulse, which is a function of force and time (ex. the area under the force/time curve). 

so yea, the video does not show an impulse (which has the units of newton*sec). it shows measured loads, which is not the same thing...

Jim Titt wrote:
The maximum force is all that is relevant in this case. The speed at which a force is applied IS important to materials scientists and engineers and is called the rate of strain, the strength of materials varies with the rate of strain. Some get stronger as the strain rate increases, some weaker and some do both, there are curves available for most materials. Because polymers usually flow they usually get "stronger" the faster the force is applied and this is the case for nylon 6.6. We are talking about milliseconds though so nothing of interest to us, the researchers stop measuring at rates of over 5000/s.

jim, i agree that the maximum force is all that is relevant. my point was, don't call the maximum force a shock load, because they are not the same thing (see my explanation to Hson above). its more semantics than anything but are important distinctions to understand.

I really like your work, Ryan. Just continue to be you, dont listen to the critics. You're doing the community a huge service, especially considering you're not getting a million views and royalty checks. You're safe, you use nice reliable gear for testing numbers, you spend your time and money doing things we all wish we could test, and you're having fun. If someone is so ungrateful for your productions that they cant skip ahead 10 seconds at a time, then dont worry about them. I'd rather you give us more than less, so keep doing what you're doing. Thanks for all the hard work and money spent to feed our curiousities.