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SRENE anchors may go the way of the dinosaur

uwhp510

13-Mar-2006
3:45:07 PM

What are you testing?

10mmx178mmCarrotBolt

13-Mar-2006
3:54:39 PM

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On 13/03/2006 uwhp510 wrote:
>What are you testing?

...his post would seem to indicate he is testing the edibility of climbing gear ...


Phil Box

13-Mar-2006
3:59:40 PM

We are dynamically testing anchor setups with realtime feedback in graphic form with inputs of something like a thousand times a second which will help us catch the peak loads. This has never before been done. I can't say too much at this stage suffice to say that the system works and the load cell type apparatus that we have developed will be able to be placed in any climbing scenario out on the cliff. We will be testing 3 point anchors with data coming from all three points as well as the powerpoint.

We have concluded testing the sytem to verify that it resolves factual real time data for one load cell type of testing device. That has been an extremely fun thing to do. We snapped an old crap static rope at about 1100 kilos and got that on video. We also confirmed without a shadow of a doubt that sideways loads on carabiners is something to be avoided at all costs i/e loading a carabiner over an edge, don't do this. Carabiners in this configuration are about a hundred times weaker than if they are loaded along the spine i/e the way they are supposed to be loaded.

Ooh I can't wait for the next round of testing to be conducted. Fun fun fun. We now have access to our own Buster the crash test dummy. He's 80kgs and he can't wait to do some factor 2 falling, poor Buster. Poor me cos I'm gunna be the other dummy who will have to do the belaying in one scenario.


cruze

13-Mar-2006
4:01:07 PM

As with all this sort of stuff we should be careful not to confuse the relative (ie equalised vs non-equalised) with the absolute (both systems are more than adequate for the vast majority of situations - I will be sticking to redundancy over "true" equalisation)...

If I wanted to belay a bulldozer taking off on the second pitch of some poorly protected horror show, I don't think it would matter what system I used. Often we don't need to attain a state of "best practice" when "good practice" will suffice. That is why we don't use 50 bomber pieces equalised or not. We use one rope (or maybe two). We use one screwgate and one belay device to both belay and rap (well maybe 2 screwgates). Perhaps the rest is more academic? Or perhaps I am a little too naive for this debate...

I will reask Jono's question:

Could someone please relate their personal experiences of complete anchor failure?...


Phil Box

13-Mar-2006
4:01:41 PM

In other news pertinent to this thread.

Here is a very concise summary of the gargantuan thread on rc.com.


anthonyk

13-Mar-2006
4:03:56 PM

On 13/03/2006 Phil Box wrote:
>Don't use static anything in an anchor. The test results so far indicate
>that the use of nylon climbing rope is preferrable to anything else for
>anchor building.

thats an interesting comment considering static anchors are very much the standard, especially if people are not swinging leads & don't want to use the rope as an anchor.

the only available source for a properly dynamic cordelette is to make off cuts of an old climbing rope because its not generally available by the metre, which makes it impractical for a lot of people. also cordelettes are generally chosen in the ~7mm range (6? 8?), which is bulky enough, but even so much, much less bulky than using off cuts of most ropes, which are commonly 10mm+.

uwhp510

13-Mar-2006
4:39:40 PM

belaying the bulldozer on the horror show is the exact situation where you would think most carefully about what system you are using, to get the best chance of not dying if the bulldozer comes unstuck.

Otherwise I agree, 99% of the time it doesn't matter what you use.

I've only heard of anchor failure second hand (eg in the Warrambungles guide) but I reckon that i've been in enough situations (especially in alpine climbing, where the anchors are often crap, eg snow stakes/axe shafts where factor two falls are more likely than in usual rock situations) to have a bit of a think about these kind of things.


cruze

13-Mar-2006
4:52:19 PM

On 13/03/2006 uwhp510 wrote:
>belaying the bulldozer on the horror show is the exact situation where
>you would think most carefully about what system you are using, to get
>the best chance of not dying if the bulldozer comes unstuck.
>
>Otherwise I agree, 99% of the time it doesn't matter what you use.
>
>I've only heard of anchor failure second hand (eg in the Warrambungles
>guide) but I reckon that i've been in enough situations (especially in
>alpine climbing, where the anchors are often crap, eg snow stakes/axe shafts
>where factor two falls are more likely than in usual rock situations) to
>have a bit of a think about these kind of things.
>
Errr... maybe I didn't make my point clearly enough. No climbing system anchor known to exist will hold the fall from a multi-tonne (ie bulldozer) object. Hence whether you use a knot or not to tie off your anchor system you are majorly screwed... That is my whole point: is this discussion of anchors a process in academia or have we all been living that one micro Newton away from total anchor failure all these years?

uwhp510

13-Mar-2006
4:59:59 PM

No you didn't understand my point.

It is in the marginal situations where these things are worth taking notice of. Most people try to avoid marginal situations, but they do occasionally arise and when they do, you want the deck stacked as much as possible in your favour.

patto

13-Mar-2006
5:29:51 PM

On 13/03/2006 uwhp510 wrote:
>OK,
>
>The crux of the matter lies in the fact that stuff (nylon webbing, cord,
>spectra, steel cable...) stretches, and provided we don't exceed the elastic
>limit of our material, stretches in the manner;
>
> F = kx (where k is the spring constant, and x is the extension resulting
>from force F)
>
>If we ascribe a length of cord (equating to one of the arms of the cordalette)
>the spring constant k1, then the spring constant of the other arm (which
>is twice as long) is k2 = k1/2 (which can be determined by treating the
>arm as two equal springs, of the length of the shorter arm, in series ie.
>1/keq = 1/k1 + 1/k2).
>
>So now we have two springs in parallel, being the two arms of the cordalette,
>one with a spring constant k1 and the other with a spring constant k1/2.
> Springs in parallel add, so keq = k1 + k2 = 3/2k. So the extension in
>the whole system, x, is due to the load F, which is the load on the belay
>and F = 3/2k1x
>
>But the tension in each arm, which is each also extended by x, is given
>by T1 = k1x and T2 = k2x = k1/2x. Thus substituting for k1x, F = 3/2T1
>= 3T2, ie T1 = 2T2.
>
>The assumptions i've made are that
>a) the two arms are directly in line, so that once loaded the system can't
>swing to the side to compensate, but since we are talking about the most
>ideal case (with no angle between the anchors, and a perfect loading direction,
>I think this is unimportant)
>b) that we can treat nylon cord/webbing as a perfect spring. I think
>that this is at least a good approximation for my purposes.
>
>If it all doesn't make sense I can draw a picture I guess.

Your assumption a) is completely wrong and impossible. I agree with your physics of the springs but from a basic static force diagram you will see that what you are suggesting is impossible. (in physics speak) The horizontal components of the tensions vectors in each cord must cancel. (horizontal is perpendicular to the fall line).
{EDIT okay, i missed the bit where you said one-dimensional}

I am going to make a few blanket statements regarding a two piece anchor setup. These apply even if arms are different length. Please if you disagree or want explanation just ask.

1. Going back to 'perfect' equalisation. If you managed to perfectly equalise the anchor and the cord is completely static then the equalisation remains perfect. This is because the angles don't change therefore the equalisation can't change.

2. However in practice you cannot perfectly equalise an anchor and no cord is completely static. Stretch often will improve IMPROVE equalisation.

{This post has been edited to remove rash statements that were made. Don't you love edit! :) }

uwhp510

13-Mar-2006
6:03:42 PM

>But this is 100% false.
>
>Your assumption a) is completely wrong and impossible. I agree with your
>physics of the springs but from a basic static force diagram you will see
>that what you are suggesting is impossible. (in physics speak) The horizontal
>components of the tensions vectors in each cord must cancel. (horizontal
>is perpendicular to the fall line).

There are NO horizontal components, because I did the analysis in ONE dimension. Any angle between the pieces will increase the loading, but it will still be shared in the ratio I've implied.

>I am going to make a few blanket statements regarding a two piece anchor
>setup. These apply even if arms are different length. Please if you disagree
>or want explanation just ask.
>
>1. Going back to 'perfect' equalisation. If you managed to perfectly
>equalise the anchor and the cord is completely static then the equalisation
>remains perfect. This is because the angles don't change therefore the
>equalisation can't change.

I will say it again, there are no angles and no such thing as completely static cord.

>2. However in practice you cannot perfectly equalise an anchor and no
>cord is completely static. Any stretch that occurs in the cord will IMPROVE
>equalisation. A really stretchy cord will give better equalisation, likewise
>static cords offer less equalisation.

This is complete rubbish because both arms of the cordalette will stretch, and the one that will stretch the most is the one that is more springy, ie the longer one, which will transfer load to the shorter arm. Try it with rubber bands.

>3. The notion that unequal arms will introduce unequal loading is flawed.
> In fact it makes no difference. If it is equalised to begin with then
>it is equalised for all loads.

Its not a notion, its a proven fact. I'll give you the statics diagram, with a nice step by step explanation, stay tuned.

patto

13-Mar-2006
6:16:35 PM

>>3. The notion that unequal arms will introduce unequal loading is flawed.
>> In fact it makes no difference. If it is equalised to begin with then
>>it is equalised for all loads.
>
>Its not a notion, its a proven fact. I'll give you the statics diagram,
>with a nice step by step explanation, stay tuned.

You are correct. My statement was false. (OOPS) :)

Sorry I should have read your post more thoroughly. I didn't realise you were looking at a one-dimensional case.

uwhp510

13-Mar-2006
6:28:53 PM

Edit:
Its okay, you beat me to it. I am 99% sure that this will generalise to the full 3d case, but I haven't bothered to check.


cruze

13-Mar-2006
6:38:25 PM

On 13/03/2006 uwhp510 wrote:
>No you didn't understand my point.
>
>It is in the marginal situations where these things are worth taking notice
>of. Most people try to avoid marginal situations, but they do occasionally
>arise and when they do, you want the deck stacked as much as possible in
>your favour.

If I come around a bend at 80 km/h in my trusty magna and see a 20 tonne semi coming straight for me, no matter how much I click my heels and think of kansas I am totally cactus. My point.

If I stick to the recommended speed of 75 km/h then MAYBE I will have time to react differently. Your point.

patto

13-Mar-2006
6:49:43 PM

Thanks for effort the diagram. I apologise for my rash dissmissal of your first statement.

I hate when I start confusing myself, with opposing thoughts. I did have all this sorted out in my head last friday, however when I tried to work out an example it quickly got too complicated and I gave up.

I won't attempt again at a diagram or calculations in the 2D case (3D is uneccessary in a 2 anchor case). However I will say that depending on the angles involved the effect of the unequal arms changes. If there is a 90 degree angle between the arms then my 'instinct' tells me for a typical level of stretch ~5%, then then the effect of unequal arms is relatively small. I won't do calculations because it hurts my head.

Have a look at what would happen in a 2D case yourself. Weight does shift to the shorter arm however this is partially offset by the fact that it stretches a smaller distance than the longer arm. Equalibrium analysis could find the final answer but the calculations are non-trivial.

10mmx178mmCarrotBolt

13-Mar-2006
8:39:13 PM

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YAAAWWWWNNNN !!!

>the final answer...

... when in doubt, use a good 'ol fashion waist-belay...


Andrew_M

13-Mar-2006
8:48:42 PM

Well, if the RC.com thread stirs people up then manufacturers might make more dynamic cordalette material. At the moment it's easy enough to buy ice floss in the 7-7.5mm range, it's just a bit bloody expensive to chop a new one up for anchor material! How bad is 7mm perlon anyway in terms of 'staticness'? Surely it stretches at least a few percent? 'Static' canyoning and caving ropes stretch a heap and you just don't notice unless you've got a big enough drop, when it becomes really obvious.

I have taken a factor ~2 onto a nylon daisy without gear or bone breakage. I put it down to the small bit of stretch inherent in the nylon...Does anyone have any hard data on this, or even better...Phil are you planning on testing nylon vs spectra cordalettes under identical conditions?

Andrew

On 13/03/2006 anthonyk wrote:
>On 13/03/2006 Phil Box wrote:
>>Don't use static anything in an anchor. The test results so far indicate
>>that the use of nylon climbing rope is preferrable to anything else for
>>anchor building.
>
>thats an interesting comment considering static anchors are very much
>the standard, especially if people are not swinging leads & don't want
>to use the rope as an anchor.
>
>the only available source for a properly dynamic cordelette is to make
>off cuts of an old climbing rope because its not generally available by
>the metre, which makes it impractical for a lot of people. also cordelettes
>are generally chosen in the ~7mm range (6? 8?), which is bulky enough,
>but even so much, much less bulky than using off cuts of most ropes, which
>are commonly 10mm+.
>
>


Andrew_M

13-Mar-2006
8:56:16 PM

Hey Cruze, not a good analogy. Sometimes, hopefully only very rarely, you just get in that position without meaning to: marginal belay, with retreat not an option. That's when that extra 10% stacking of the deck could make a real difference.

And as for asking for people's personal experiences with anchor failure? Perhaps those folks who have had anchors fail aren't in a state to reply...

On 13/03/2006 cruze wrote:
>If I stick to the recommended speed of 75 km/h then MAYBE I will have
>time to react differently. Your point.

10mmx178mmCarrotBolt

13-Mar-2006
9:10:31 PM

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On 13/03/2006 Andrew_M wrote:
>And as for asking for people's personal experiences with anchor failure?
>Perhaps those folks who have had anchors fail aren't in a state to reply...

...Mikl has the ' personal experiences ' AND the scientific-academic background to sort most if not all of this fascinating.........dried dog sh#t...


cruze

14-Mar-2006
9:25:26 AM

On 13/03/2006 Andrew_M wrote:
>Hey Cruze, not a good analogy. Sometimes, hopefully only very rarely, you
>just get in that position without meaning to: marginal belay, with retreat
>not an option. That's when that extra 10% stacking of the deck could make
>a real difference.
>
>And as for asking for people's personal experiences with anchor failure?
>Perhaps those folks who have had anchors fail aren't in a state to reply...
>

Extra 10%? Count me in... Extra 0.1% gain in strength? I will stick to the unequalised equalised cordelette for redundancy and simplicity and throw another piece or five into the belay. My point about complete anchor failure is that there are probably a whole heap of other factors that led to that conclusion and that a SLIGHT increase in strength wouldn't have helped at all.

Also as for the "staticness" of a belay system, I can only assume that these tests are being conducted with a dynamic rope involved somewhere. Bungy jumping on high tensile wire isn't a good model for the real deal.

I really don't want to have my head in the sand on this one, but I don't want people going out there misrepresenting the reality of the situation under the heading of "science".

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