How do you add up an anchors KN?
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Hello, |
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I'm not quite sure I understand the question. As I understand, you're asking "How do I calculate the breaking strength of my anchor?" |
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Nobody really knows the formula. It involves calculus, trig, statistical probability, and alcoholic consumption. |
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This all came about after a guided trip. The guide was required to build a 25 kn anchor at the minimum and that got me thinking about how to add that up? |
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johnnyrig wrote:Nobody really knows the formula. It involves calculus, trig, statistical probability, and alcoholic consumption. alcohol consumption is the real kicker here. very important to the equation. Nobody really knows but I believe the ratio is exponential and starts off around 1 drink : -1 kn. |
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They likely were just referring to the kn rating of each piece added together. I.E. 2 cams at 12kn each plus a small nut at 6kn would equal 30kn. Of course the anchor probably wouldn't actually hold 30kn due to the reasons listed above, but thankfully we don't need it to! Just sounds like a general guideline. |
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My anchors have one of two ratings: |
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unless you're taking high FF falls on the anchor, it doesn't have to hold much. i could be wrong but i'm pretty sure the top piece takes 1.6x the force on the climber and the belay take .6x the force on the climber. and at around 8Kn the climbers organs start to disintegrate. so, in reality, if the belay is taking more than 5kn in a typical fall you have bigger problems (dead climber) |
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eli poss wrote:unless you're taking high FF falls on the anchor, it doesn't have to hold much. i could be wrong but i'm pretty sure the top piece takes 1.6x the force on the climber and the belay take .6x the force on the climber. and at around 8Kn the climbers organs start to disintegrate. so, in reality, if the belay is taking more than 5kn in a typical fall you have bigger problems (dead climber)huh? |
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FrankPS wrote:My anchors have one of two ratings: 1. Good 2. Good enough3. Just don't fall. |
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I wonder whether the guide's "25 kN anchor" was ever tested with a 25kN load. I bet not... |
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the 25 kn of the pieces wont matter much if it was equalized with the standard 6mm cord rated to around 7 kn. doubled at the master like happens most times and youll get 14 kn max. |
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I've seen something like this used as guideline when teaching people to build gear anchors. As this was a guide on a trip talking to a client, maybe that is where this came from? |
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I'll try to iterate what eli was trying to say: |
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Here you go climbing friend. |
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rgold wrote:I wonder whether the guide's "25 kN anchor" was ever tested with a 25kN load. I bet not...exactly my thought. every guide I've been out with just used common sense. |
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I don't recall ever hearing of an anchor failing because the placements in it (nuts/cams/etc) all broke. |
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csproul wrote: huh?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 |
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Schalk wrote:In which case you would just add the kN ratings of all the pieces in the anchor together.This is wrong. assuming all the pieces share the load perfectly equally (basically never happens in reality) the strength of the anchor would be the strength of the weakest piece x the number of pieces. for example, if your weakest piece was a small nut rated to 5kn and you had 3 pieces, your theoretical strength would be 5x3= 15kn. in reality, though, 1 piece will take most of the load and pieces will usually rip before they reach their load limit so all of the theoretical stuff doesn't really matter. what does matter is that you get at least two, preferably 3 or more, very strong, reliable pieces in for anchor and try to do a decent job of equalizing them and, most importantly, don't fall directly onto the anchor. |
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Well, gee if the top piece holds, I guess you don't need the anchor to hold anything, right? |
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of course you build your anchors to strong enough to hold a factor 2 fall. if you don't even attempt to do this, you are a dumbass and you really should stick to sport climbing. but, in reality, anchors are very rarely subject to high factor falls as we also take measures to attempt to prevent this, such as leading past the anchor to get the "jesus piece" in before even starting the next pitch. i was just trying to explain why the OP's concern with calculating the total strength of an anchor is, for the most part, not useful, even if it was possible. |