ACR Anchor Method?

Jim Titt wrote: It may seem counterintuitive to you but it is however accurate and completely logical. We aren´t stupid enough to spend considerable amounts of time and money without knowing what we are testing so the various methods are compared for accuracy first and also because it is sometimes nescessary to use a different method anyway

I'm not attacking you, Jim, I'm asking the questions anyone would ask when thoroughly vetting an experiment. If I had a peer-reviewed paper in front of me, these are questions that the paper would have answered preemptively. Considering that I don't, I'm obliged to ask them. And I'll have more.

Eventually I'll update the document on the ACR. I won't include any information that I haven't been able to thoroughly evaluate.

I'd be asking these same questions if you were the ghost of Isaac Newton.

patto wrote: How do you figure that? How much strength are you wanting in you anchor arms and what are you pieces rated at? How about just using the damn climbing rope if you are so worried.

Hello Patto:

These big numbers all sound very theoretical until you consider the DMM results: They took dyneema and nylon slings, rigged them as if they were an anchor, attached an 80 kg mass (176 lb) , and then let the mass fall a *very* short distance - like 1/2 and 1 body length. Unknotted slings had no problem. The label says they won't fail until thousands of Newtons, and they don't. But if you KNOT the slings - FORGET IT. Dyneema breaks pretty much every time with any kind of knot. Nylon breaks some of the time, with any kind of knot. This is NOT putting a pickup truck on your anchor; it's the weight of a burly climber, or a small climber with a pack. THAT is what's so sobering. THAT is what should really make people think. Let's add to that the presence of sharp edges, the fact that all my slings are old and degraded, they can be degraded by wetness, etc. etc. So, if you're knotting your slings and you think you have an anchor that can stop a truck, you're badly mistaken. That's true ONLY if you have NO KNOTS.

You are correct, they compared climbing rope and no problems at all. This is why I'm thinking that a non-knotted device plus backup on the best piece with climb rope is a pretty good setup; no knots in slings, only one knot to remove in climb rope after, not too much length of rope used.

It's important that you view the right DMM videos, there are many of them.

More dramatic, with some exploration of “shock loading”

www.youtube.com/watch?v=Vrgadjo9niY&t=151s

Slower, more data:

dmmclimbing.com/knowledge/h…

Previously I referred to another poster's link, but that DMM video is the wrong one (it's mostly what happens to dyneema cord that is knotted, not knots in the usual sewn slings).

Brian L. wrote: Please link to your sources so we don't have to go hunting for them. .

Dear Brian: Actually, your request was really helpful here (someone linked to another DMM video that was not so relevant). Thanks. Here ya go:

More dramatic, with some exploration of “shock loading”

youtube.com/watch?v=Vrgadjo…;t=151s

Slower, more data:

dmmclimbing.com/knowledge/h…

Again, I must emphasize: Knots are much worse than most people think, they break under small falls with realistic masses. I thought my anchors could hold a truck. If you knot them, forget it. DMM tests show that an 80 kg (176 lb. or one burly climber or small climber with pack) mass in a fall of less than a body length breaks most slings if they're knotted in any way... doesn't break them if they aren't knotted, and will never break a climbing rope. As the video explains, this is more extreme than typical, but I climb with old slings with sand in them and water, there are sharp rocks for the slings to fall over, etc. etc. This is really something to think about and acknowledge.

I'm starting to like the idea of a knotless sling system, not dyneema, backed up by my lead rope on the strongest piece. gives redundancy and some load sharing. Only one knot on the rope to untie to leave.

thepirate1 wrote:This is NOT putting a pickup truck on your anchor; it's the weight of a burly climber, or a small climber with a pack. THAT is what's so sobering.

Wrong. The weight of a burly climber is 0.8kN. The force the knotted slings failed at were over 11kN aka the weight of a small car.

And like I said what are you expecting your gear to hold. What are your nuts and finger sized cams rater for?

thepirate1 wrote:Knots are much worse than most people think, they break under small falls with realistic masses.

Unrealistic falls though. Read about fall factors. A small fall like in the video with a HUMAN body would result in much lower forces.

The DMM test videos involve forces that are virtually impossible to occur in climbing.

thepirate1 wrote: www.youtube.com/watch?v=Vrgadjo9niY&t=151s Slower, more data: dmmclimbing.com/knowledge/h… Again, I must emphasize: Knots are much worse than most people think, they break under small falls with realistic masses. I thought my anchors could hold a truck. If you knot them, forget it. DMM tests show that an 80 kg (176 lb. or one burly climber or small climber with pack) mass in a fall of less than a body length breaks most slings if they're knotted in any way... doesn't break them if they aren't knotted, and will never break a climbing rope. As the video explains, this is more extreme than typical, but I climb with old slings with sand in them and water, there are sharp rocks for the slings to fall over, etc. etc. This is really something to think about and acknowledge. I'm starting to like the idea of a knotless sling system, not dyneema, backed up by my lead rope on the strongest piece. gives redundancy and some load sharing. Only one knot on the rope to untie to leave.

The best argument against an extending anchor is in the data from your first video. The extending, sliding X anchor see's at least twice the peak load of of the non extending anchor. In the case of the dyneema sling it's about three times the load.

But, you're missing the point of this testing. The conclusions to draw isn't "knots are bad, don't use them". In fact, the correct conclusions are spoken by the presenter at the end of the video.

1) The rope is the best anchor material for load mitigation
2) If you want to use slings, don't clip in directly, but use the rope to connect to the anchor. (again, load mitigation)
3) If you do clip in directly to the sling anchor, don't allow slack to develop, don't climb above the anchor, etc (again, load mitigation advise)
4) If you do climb above you gear, the consequence is pain/injury (because of the high loads generated by falling onto an inelastic material).

On the 2nd video, again this is looking at fall directly onto a sling. In this case it's a single sling.

The specific situation this video is looking at is using a sling as a tether. And from this it basically concludes the same thing as above.

1) Tether with the rope
2) If tether with a sling, don't have slack in it.
3) Don't climb above your tether.

So in relation to anchors, you might predict that this represents a single arm of your anchor. So you have at least 2, and usually three of these arms in an anchor. The lowest load a sling broke at was 10.2 kN (or about 2300lbs). So, in order for your anchor to completely fail, the load on the climber would have to be enormous. Realistically the peak load a climber might see in an absolute worst case scenario would be around 10Kn-11kN (for example the UIAA peak load rating of my rope is 8.9kN - UIAA tests at fall factor 1.77). IF all that load was concentrated on one leg you MIGHT bust that leg (but realistically you'd probably pull the gear out before the material failed), but there's redundancy for this reason.

So the lesson here is really: don't statically fall onto your anchor. Always have a dynamic element (the rope) between you an your anchor. The first video also highlights the pitfall of extension.

thepirate1 wrote: Again, I must emphasize: Knots are much worse than most people think, they break under small falls with realistic masses

One reason I like using 7mm nylon for rigging anchors is its knotted strength. When we first started experimenting with the ACR we were concerned about the extension limiting knot (we used a parallel overhand knot, which is fast to tie but looks dubious).

We asked Jim Ewing at Sterling Ropes to test it for us, and he found that the knot held 12kN even when sloppily tied. Which meant that the knotted strand all by itself could hold a factor-2 fall.

Ewing got the same results with 6mm Technora, a material I have no experience with. We don't know about Spectra/Dyneema or any of the other fibers or blends.

BTW, anyone who is interested, here is a good paper detailing the difference between a human load, and a load of steel plates (in the context of understanding/validating the use of a human analog mannequin for rescue testing purposes).

itrsonline.org/PapersFolder…

The conclusions are very interesting. Basically a steel plate is appropriate if testing to understand strength, OR if a system is significantly dynamic that the impact of the dynamics of a human body are insignificant compared to that of the system itself (in which case it produces conservatively high results).

It is not appropriate for determining if a particular scenario does break a system, or to determine realistic estimates of the forces generated by specific scenarios

So in regard to the video's here, you can't use the result to judge the realistic performance of the system (if it breaks in the real world when a person of the same weight falls like the mass in the video) because it is a static system, and the primary energy absorber is the load itself (your body in the real world).

For instance, in the above paper they performed a 8" drop onto a 66" length of steel cable. The load the human produced was about 650lbs(2.9kN). The load of the steel weight was about 2300lbs (10.2kN). BIG difference.

So, I would conclude that your statements about:

thepirate1 wrote:DMM tests show that an 80 kg (176 lb. or one burly climber or small climber with pack) mass in a fall of less than a body length breaks most slings if they're knotted in any way

ignores the fact that the mass reacts very differently than a human body, and produces MUCH higher loads in this loading scenario. The video's do show us the limits of these systems, but again, in terms of using them for an anchor, the strength is still sufficient, especially keeping in mind the points in my earlier post.

True enough but until we get some human cadaver testing we will never know exactly how much the body reduces the impact forces though there is work which suggests it is only to a limited effect since our "squashiness" has limits.
On the other hand I´ve seen forces 32X the original weight on one leg of an anchor doing leg-failure testing on three-point systems and that was not including a falling climber in the scenario, just the belayer weight. Add a climber taking a FF2 onto the system and I´d guess you could be looking at doubling that easily.
Both McKently and myself abandoned further testing as the slings themselves broke but there are convincing arguments that the forces could be far higher in the wrong circumstances. Both of us were working with extensions of less then 12" though he used a higher weight than I did as he was concerned with rescue loads.
The interesting thing is you cannot predict which of the remaining peices takes the highest force (they don´t "equalise" naturally enough) as the karabiner from the failed leg jams into the centre point and appears to either lock one strand or the other.

rgold wrote: Here is a method for tying in with the rope that is somewhat standardized and works for many situations. But there are times when some ingenuity and creativity are the best tools for adapting to what is available.

RGold, Thanks for the the picture of your rope anchor...can you elaborate where you say:

"Free strand must be clipped to 'power point' with another biner in order to distribute load for belay escape"?

I'm trying to visualize how clipping the free strand to the powerpoint does anything, presuming I'm belaying the leader from my belay loop, and the leader has fallen, and is either hanging off gear above me or worst-case--hanging off my belay loop below me? Or is that the point of clipping it into the powerpoint, so that the rope is redirecting through it if the leader falls before placing anything?

Jim: as usual, a lot of data here that I just can't square away with other published tests. That you should get a high multiplication factor for the forces of just the belayer going from a simple static hanging to falling on the full extension of an anchor made of static cordage is hardly surprising. In the same vein, the McKently tests, concerned solely with rescue loads, were done on 100% static systems (including static rope), which greatly magnifies any load multiplication.

However, extrapolating that to say that adding the leader's FF2 on a dynamic rope to the mix and you could easily double those already-high multiplication factors does not make sense to me. As you indicated yourself, the DAV tests showed 40% higher load overall when one leg of a sliding X blows with no extension limitation and with both the leader's offset/swinging FF2 (on a dynamic rope) and the belayer's fall (on the static webbing anchor in a 100% hanging belay situation). That's a multiplication factor of 1.4 in pretty extreme circumstances. With the belayer properly stanced and braced on even a small ledge or a couple of decent footholds and with extension limitations that make it very unlikely that the blown arm would launch him into free fall, the multiplication factor would be much less.

ebmudder wrote: RGold, Thanks for the the picture of your rope anchor...can you elaborate where you say: "Free strand must be clipped to 'power point' with another biner in order to distribute load for belay escape"? I'm trying to visualize how clipping the free strand to the powerpoint does anything, presuming I'm belaying the leader from my belay loop, and the leader has fallen, and is either hanging off gear above me or worst-case--hanging off my belay loop below me? Or is that the point of clipping it into the powerpoint, so that the rope is redirecting through it if the leader falls before placing anything?

During the course of a belay escape, you might have to transfer the loaded rope from your belay device to a strand of rope coming off the anchor. In the photo I posted, the strand "coming off the anchor" only loads the right-hand piece. Clipping this strand back to the power point and then loading it means that the load will be distributed to the entire anchor.

jktinst wrote: With the belayer properly stanced and braced on even a small ledge or a couple of decent footholds and with extension limitations that make it very unlikely that the blown arm would launch him into free fall, the multiplication factor would be much less.

You are already departing from a worst possible case to selective one, you might as well might have a 200kg weightlifter wedged behind a huge boulder and say the belay was never loaded at all.
In the climbing industry we have to look at worst cases because sure as sh*t somewhere, sometime they are going to happen. At best we can make the equipment so it will withstand a worst-case scenario OR we can warn that the equipment will not cope.
One scenario that you could look at is a FF2 lead fall directly onto the belayer who locks off and one leg of the anchor failing.

Jim Titt wrote: ...One scenario that you could look at is a FF2 lead fall directly onto the belayer who locks off and one leg of the anchor failing.

That's precisely the DAV test conditions and even there, the "shockload" was "only" a 40% increase in the load , right? I know that's not nothing but it's a far cry from "many times more".

Hi everyone,
does anyone know if this thing about knots in dyneema slings reducing the strength by 40% or more still holds true for old, used, slings?
Thanks

jktinst wrote: That's precisely the DAV test conditions and even there, the "shockload" was "only" a 40% increase in the load , right? I know that's not nothing but it's a far cry from "many times more".

Well no, the DAV test was with the HMS on the belay and the belayer hanging below, if the belay device is actually attatched to the belayer and they are directly attatched to the master point things are different. In fact the "belayer" weight was attatched to the belay by a length of rope and the real belayer standing on the ground well out of the way.

Derek W wrote: I use a standard OP ring and it works fine. I would rather something a little larger, but it'll do.

You can pick up all sizes of rings from your local rigging supply shop. I've got a 4" one

rgold wrote: During the course of a belay escape, you might have to transfer the loaded rope from your belay device to a strand of rope coming off the anchor. In the photo I posted, the strand "coming off the anchor" only loads the right-hand piece. Clipping this strand back to the power point and then loading it means that the load will be distributed to the entire anchor.

Thanks for that clarification!

David Coley wrote:Hi everyone, does anyone know if this thing about knots in dyneema slings reducing the strength by 40% or more still holds true for old, used, slings? Thanks

In theory, the strength reduction is an uneven distribution of forces throughout the material, so shouldn't change the reduction amount for old slings. What will change, however, is the effective strength, because old used won't be as strong as new slings. Depending on the wear and tear on the sling, a 40% reduction may or may not put the strength at lower than acceptable levels. If your sling is so worn it only has 25% of the original strength, 5.5kn, then a 40% reduction puts it in the realm of aid gear strength.

Jim Titt wrote: Well no, the DAV test was with the HMS on the belay and the belayer hanging below, if the belay device is actually attatched to the belayer and they are directly attatched to the master point things are different. In fact the "belayer" weight was attatched to the belay by a length of rope and the real belayer standing on the ground well out of the way.

In a lead fall + hanging belayer + blown-leg test, sure, it makes sense that with the belayer's weight clipped directly to the anchor's central point, you'd get a higher load multiplication than if it was tethered through a dynamic tether. Basically, this makes the case for always tethering with a dynamic tether, be it the rope, a Béal dynaconnexion, a Petzl Connect, a length of dynamic rope with a Kong Slyde, etc. (which is what I do and which has been discussed elsewhere on this thread).

I also still feel that it confuses the issue to use as your reference point for load multiplication in a blown-leg scenario the simple static weight of the hanging belayer. From what I understand, Ioad multiplication as a result of anchor extension usually means the multiplication factor between the fall getting arrested on the full/intact anchor and the same fall arrested with one anchor leg blowing.

Talking about worst case scenarios: how about comparing a quad, a cordelette and a statically-equalized dynamic rope anchor (à la rgold) on a 2-leg anchor with legs of significantly different lengths and a 5kN fuse on each leg (with the anchor pre-equalized for a straight-down load, not pre-equalized in a direction other than down)? We're not talking about manufacturing gizmos that may fail or be misused here. Just having useful information to help understand in what circumstances some types of anchors might be safer than others.

Finally, the main reason I started posting on this thread (despite determinedly abstaining from it when it first started) is because I am still trying to understand why your load distribution results (no blown leg) for the simple two-leg sliding X are different from the DAV's. Several years back, you reported a 1:3.7 distribution ratio for the sliding X pre-equalized in a direction other than down and tested on a drop tower with the weight on a track, which I found mind-bogglingly uneven. Could it have been a typo? On this thread, your numbers are more reasonable: 1:1.7 or 1:1.9, depending on the post, and you're also reporting (for the first time, as far as I know) a comparison between different equalization testing methods. With the DAV tests, from what I can see without understanding German, it seems that they got a 1:1.3 distribution when the weight mimicking the leader was dropped from 3m up and 1m to the left of the sliding X's central point (edited to add: again, with the weight mimicking the belayer hanging statically from the anchor) .

Any discussion of the possible reasons for the differences would be most welcome. So would details of the 4 different methods you compared for the two-leg sliding X.

PS: I think I've seen your "3-leg sliding X" referred to as a "sliding W" before. Has anyone else?

jktinst wrote: I also still feel that it confuses the issue to use as your reference point for load multiplication in a blown-leg scenario the simple static weight of the hanging belayer. From what I understand, Ioad multiplication as a result of anchor extension usually means the multiplication factor between the fall getting arrested on the full/intact anchor and the same fall arrested with one anchor leg blowing.

Reasonable people can disagree about what to test, but if the belayer is hanging to begin with and a leg blows, then entirely forgetting about the peak load generated by the falling climber, you've got climber plus belayer (so a 160 kg "entity") taking what might be high fall-factor fall onto what remains of the anchor. (The fall factor in this case is the anchor extension divided by the length of the belayer's tie-in.)

The original point of such observations was to point out that relatively small anchor extensions could still lead to substantial anchor loads if the belayer is tied in short and pulled off.