How do you add up an anchors KN?

eli poss wrote: when you fall, three thing take force: the falling climber, the belayer, who is tied into the anchor, and the top piece. because the top piece acts like a pulley, it takes the force on the climber + the force on the belayer, which adds up to be about, IIRC, an average of 1.6x the force on the climber. this means that the belayer takes about .6x the force of the fall on the climber. this info is just stuff off the top of my head, coming from the results of some testing, probably done by john long (i think thats the right name- the anchor guy who came up with the cordallete) or jim titt or somebody else. i'm sure bearbreeder or jim titt or somebody else could easily post those test results but i don't really remember where exactly that info came from. i also recall reading somewhere that when the human body is subject to around 8kn force, your organs start to disintegrate. so if your belayer is subject to ~4.8kn the climber is subject to ~8kn, which is lethal. and since this doesn't happen in reality, we can conclude that the belay anchor isn't subject to this force (4.8kn) unless you're taking high fall factor falls on the belay anchor, which will drastically increase impact force. somebody who is more knowledgeable, please step in and explain this better than i can, or correct me if i'm wrong

Way too much wrong to correct. Just scrap this. We can start over.

When you fall three things take the force? Um. No. Many things do, especially the rope.

Max force 8kN? Things start to disintegrate? Wow. Good stuff. Hello. Many ropes are rated higher than this. Max allowable by UIAA is 12 in UIAA test.

Oh god. I can't go on. Just delete your post. Too much bad info.

Greg D wrote: Way too much wrong to correct. Just scrap this. We can start over. When you fall three things take the force? Um. No. Many things do, especially the rope. Max force 8kN? Things start to disintegrate? Wow. Good stuff. Hello. Many ropes are rated higher than this. Max allowable by UIAA is 12 in UIAA test. Oh god. I can't go on. Just delete your post. Too much bad info.

can you provide a source that disproves what i posted or are you just pulling this out of your ass? and i'm sorry that i worded that shittly: yes more than three things take force in a fall. when we measure the force, though, we measure the force taken by 3 things: the falling climber, the belayer, and the top piece. and the reason ropes are allowed to have an impact force of 12kn is because this 12kn is not the force on the falling climber: it is the force on the top piece. a fall that puts 12kn on the top piece will put about 7.5kn on the falling climber.

ChrisCase wrote:Hello, I've searched and searched on this site, but can't seem to find my answer. When it comes to adding up the KN of an anchor, how do you add it? I thought you just added in the KN of the protection (cam, stopper, etc) but what about everything else? Do I add the biners, slings, cord, etc? Any help would be greatly appreciated. I've read two anchor books as well, but there's nothing in there on this topic. Chris

take the SINGLE strongest leg of your anchor ... and treat that as the "strength"

while we theres this fancy stuff called "equalization" ... self equalizing methods arent what they are all cracked up to be ... and the fixed equalization methods arent really "equal" with different length legs or a slight change in angle ...

so conservatively, your best piece is your "strength" ... the other pieces are just redundancy in case that piece blows out

if you want to do exacto-mundy fancy intrawebz calculations ... youll never be able to do it in real life on real rock, in a real climbing situation ... those fancy multi page "its this many KN" numbers are absolutely irrelevant in the real world as youll never be able to pull out yr TI-83 on a pitch and punch in the numbers, nor does the rock give a damn

what you CAN do is have some basic rules of thumb to maximize the "survivability" of your anchors .... again nothing involving fancy numbers

as someone above said ... unless yr using microgear, the gear itself wont fail, its the placement that will

;)

eli poss wrote: can you provide a source that disproves what i posted or are you just pulling this out of your ass? and i'm sorry that i worded that shittly: yes more than three things take force in a fall. when we measure the force, though, we measure the force taken by 3 things: the falling climber, the belayer, and the top piece. and the reason ropes are allowed to have an impact force of 12kn is because this 12kn is not the force on the falling climber: it is the force on the top piece. a fall that puts 12kn on the top piece will put about 7.5kn on the falling climber.

Wrong again. Stop it. You are still posting wrong info.

Sorry Eli, Greg is right, you've got a lot of things either confused or wrong.

How much the human body can take is, as it stands, so poorly posed a question as to have no answer. It depends on a host of factors, including for example the way the load is applied, its duration and direction, as well as what one considers to be the mechanism of injury (for example injuries caused by acceleration as opposed to injuries caused by blunt or sharp trauma).

The 12 kN number adopted by the UIAA apparently comes from tests performed by the US Army for parachutists, and is indeed represents a load applied to the body by a parachute harness and has nothing to do with climbing protection or how much force climbing protection might experience.

The closest thing to the climbing situation is industrial fall-arrest harnesses, which typically absorb fall energy via screamer-type stitch-ripping mechanisms. Industry standards seem to run at something more like 6 kN for an acceptably safe maximum impact load for a factor 2 fall.

There's some information and references here hse.gov.uk/research/hsl_pdf… .

eli poss wrote: and the reason ropes are allowed to have an impact force of 12kn is because this 12kn is not the force on the falling climber: it is the force on the top piece. a fall that puts 12kn on the top piece will put about 7.5kn on the falling climber.

The UIAA fall test force is the force on the climber, not the top piece. See UIAA 101 (Ropes) in theuiaa.org/safety-standard…

I second getting the Long/Gaines book "Climbing Anchors" to get a handle on more of the theory. You'll get a sense from reading it that anchor-building really is an art in that when faced with building one that your life depends on, having the ability to assess and improvise based on theory but not owned by it is where you probably want to be. As has been stated, it's the quality of the placements that's most important - in Climbing Anchors they ran tests showing that certain types of anchors equalize better than others, but as long as the placements are sound almost all the anchor types tested were "good enough" (i.e. we don't die).

If it's numbers you want however, there is a nice little quantitative exercise I found on the interwebs from a British climbing instructor that I have been using to double check my three-piece anchor placements. She recommends rating each individual placement on a 1-5 scale, 1 being totally sketch to 5 being completely bomber, no worries. You rate each placement 1-5 and if the three individual ratings add up to a total of 10 it's good to go. Of course the weakness of this approach is you have to know what a good placement looks like in the first place, but again Climbing Anchors (and a mentor/instructor) can help with this. Start at RDCS (Running Dogs Chase Squirrels) for nut placements and go from there. Hope that helps.

Dylan B. wrote: To the OP: the short answer is that the "strength of your anchor," is the strength of your weakest piece times the number of pieces.

You are assuming then that the total strength is (at least) the sum of the strengths of the individual pieces, and this is the assumption of perfect equalization, which we know is generally far from achievable.

As I said before, there is probably no one who can set up an anchor and (even with their TI 83 at hand) say anything consistently numerically accurate about the load it can take. And as I also said, even the judgements that are made, say things like bombproof, good, fair sketchy, have, never been subjected to actual objective testing. People learn by having someone else who has never had their judgements tested evaluate their anchors---its all done with visual cues and "common sense."

The engineering response to the practical level of ignorance we have is redundancy, hence the standard three-piece anchor which, when we judge the individual pieces to be good or better than good, we hope will be up to all possible tasks. This assumption is so rarely tested by a worst-case scenario load (in my experience, we hear about a total anchor failure in the field about once every ten years) that we have little idea whether even it is practically effective.

The almost complete absence of decisive practical experience being what it is, the role of theory, properly interpreted and not viewed as realistically infallible, is actually more important, not less important, than it might be otherwise. Cams are the perfect example of this. You can plug 'em in and clip 'em without knowing a cosine from a stop sign, and you can heap scorn on anyone who refers to such esoterica (actually just high school math) in their posts, but cams exist and work only because someone (Ray Jardine I suppose) knew enough engineering math to deduce the appropriate cam shape.

rgold wrote: And as I also said, even the judgements that are made, say things like bombproof, good, fair sketchy, have, never been subjected to actual objective testing. People learn by having someone else who has never had their judgements tested evaluate their anchors---its all done with visual cues and "common sense."

An Experimental Methodology for_the Assessment of Climbing Devices Actual Strength

An Experimental Methodology for_the Assessment of Climbing Devices Actual Strength

An Experimental Methodology for_the Assessment of Climbing Devices Actual Strength

the caveat is that those "estimators" were experienced ...

theres additional literature somewhere that shows that experienced folks are quite decent at evaluating gear "strength" while new folks arent so good ...

im going climbing soon, so ill leave finding that documentation up to da MP brigade today

;)

eli poss wrote: ... and the reason ropes are allowed to have an impact force of 12kn is because this 12kn is not the force on the falling climber: it is the force on the top piece. a fall that puts 12kn on the top piece will put about 7.5kn on the falling climber.

"The impact force of a rope is the force transmitted by the rope to a mass in the standard test. The measurement is made at the falling mass, climber side."
petzl.com/en/Sport/What-is-…

"Impact force
This rather evocative term means the force transmitted to the climber at the moment a fall is arrested."
thebmc.co.uk/rope-markings-…

eli poss wrote:and at around 8Kn the climbers organs start to disintegrate.

Absolute rubbish.

eli poss wrote:at around 8Kn the climbers organs start to disintegrate.

Jim Titt wrote: Absolute rubbish.

Lol!

Well if someone put 1600 pounds onto my sensitive organ(s) then I'm not sure how it would cope! ;-)

But of course when we talk about forces it is all about how and where they are applied. When it comes to to distributed forces and high acceleration then Colonel Stapp experienced much higher forces and accelerations.
(No doubt Jim is already aware of this.)

That said I would expect bruising from a fall that reaches anywhere near 6kN.

My three cents:

An anchor is only as strong as its shittiest component.

An anchor is only as strong as the mind of the one who built it.

An anchor should never have to withstand 25 kN of force, I'm pretty sure that would kill everyone attached to it even if it did hold.

Dylan B wrote: ...the formula I provided is the shorthand that his guide was using, and that was the question. I included the caveats to cover all that you added here.

What you said is

Dylan B wrote:...the short answer is that the "strength of your anchor," is the strength of your weakest piece times the number of pieces.

This is wrong, to put it a little less gently. If the point of your caveats is that this rule of thumb is wrong, then fine. But why would you deliberately post something that is wrong and then take it back? Wouldn't it make more sense not to say it at all?

Bearbreeder gave a much better rule of thumb, if such things are required and useful.

bearbreeder wrote: the caveat is that those "estimators" were experienced ... theres additional literature somewhere that shows that experienced folks are quite decent at evaluating gear "strength" while new folks arent so good ... im going climbing soon, so ill leave finding that documentation up to da MP brigade today ;)

this is very interesting to me. do you have a link to the original source? i'd like to read more about this test.

patto wrote: Lol! Well if someone put 1600 pounds onto my sensitive organ(s) then I'm not sure how it would cope! ;-) But of course when we talk about forces it is all about how and where they are applied. When it comes to to distributed forces and high acceleration then Colonel Stapp experienced much higher forces and accelerations. (No doubt Jim is already aware of this.) That said I would expect bruising from a fall that reaches anywhere near 6kN.

Car seat belts (depending on type) have to withstand around 26kN, commercial aircraft seats 16g, F1 racing car shells 80g and so on which tells us what other industries think are survivable forces.
There are a number of data-logged accidents where race drivers have survived impacts in the 50 to 75g region and the two records are a calculated 179g for Dave Purley (F1) and Kenny Brack with a logged 214g.
I know a climber who managed an impact of 27g (he broke a quickdraw in the process) and walked away cursing.

eli poss wrote: this is very interesting to me. do you have a link to the original source? i'd like to read more about this test.

http://www.caimateriali.org/fileadmin/user_upload/pdf_marra/An_Experimental_Methodology_for_the_Assessment_of_Climbing_Devices_Actual_Strength.pdf

I'd seen this test and, at the time had discounted it as perhaps not addressing the real judgement question. The authors themselves suggest this more than once. My thinking at the time was that the placements themselves seem to have been excellent, so what the climbers were estimating was the load at which the gear would break, something a reasonably knowledgeable person could be expected to be much better at than judging placement failures loads. (In the case of cams, it is true that at least one type of cam pulled out of the placement rather than breaking, however.)

Even in this case studied, although experienced climbers look pretty good as a group at this (I would say) restricted task, the range of their guesses, for example in the case of cams, is more than double the actual range of failure values. It would have been nice to include a scatter plot and correlation data to get a better sense of how good climbers were at estimating.

I've mentioned that I've heard of the catastrophic failure of a belay anchor about once every ten years. As far as I can recall, none of these failures involved broken gear.

This concept of [n x the weakest piece] is wrong, and here's why:

Imagine I have a dead-vertical, perfect .75 Camalot crack in solid granite.

If I place 3 .75 C4's (14KN) and equalize with a cordelette and a BFK - using the heuristic in question I have a 42 KN anchor - or stupid-bomber-gnar-gnar awesome in normal parlance.

Now imagine I add a 4th piece equalized into the system, except this time it's a .75 X4 (9 KN) - using the heuristic in question I would lower my strength to 36 KN - which of course is silly to think.

At least that's my two cents.

Dylan B. wrote:C'mon guys, this is a good question for a beginner to ask. OP: I recommend John Long's book Climbing Anchors. What you'll see is that the amount of force transmitted to each leg of the anchor is related to the angle between the legs. If each leg is within a narrow angle of the others and they're well equalized, then each piece takes only 1/3 of the force of the fall (read the book, it'll explain the physics). Then the maximum rating for the anchor is 3x the strength of the weakest piece. (If you have an 8kn nut, a 12kn cam and a 10 kn cam, a 24kn force would cause that nut to fail). This is obviously very simplistic. Real-world systems require that you factor in a lot more. But that's the basic theory that your guide was following to "calculate the strength" of the anchor. This is also not something you're really going to do in the real world in your own climbing. You're going to find the 2-4 best pieces you can get and equalize them appropriately, tie your master point and go. If your pieces are sketchy, you're going to find other placements. You will almost certainly find yourself building anchors where the weakest piece of three is only 6 kN, but you're confident in the bomber #3 that's beside it.

I have read the books, but still don't see anything on how to add up the KN. It does say that for safety standards we make our anchors 4 to 5 times stronger than needed, and that a 3 piece anchor could hold more than 40kn. So how are they adding that all up? Is there any guides out there that can shed some light for me?

For a 25kN anchor.... add up the three weakest isolated points. Suppose you have a nut, and two finger sized cams. See each arm of the anchor as independent and look for the weakest point... the cam or nut should be. Add those together, and you can get in the general region of what the sort of fall it could withstand. Where the math gets complicated. The angles between each piece and the master point can act as multipliers for impact force. Mostly that aspect is ignored for this calculation. Most of us guesstimate.