kN and micronuts

Question spawned from cleaning gear after working a shift of calculating crazy drip rates and med dosage. If one places 2 DMM Peanuts (for example), each with a 4 kN rating, and uses them together with a sling or whatever as one piece of protection, is kN now simply doubled to 8kN? Seems too simple...

I know I have read about this before on a forum here, but can't find it in the search. All I can find is about how to place opposing nuts in a horizontal, and doesn't ever mention the kN.

I have always connected the 2 pieces with a sling that has a overhand and master point, like a mini 2 piece anchor, what other ways are there?

Placing two nuts does not double the strength. Placing nuts in opposition in a horizontal is about redirecting the load direction.

Allen Sanderson wrote:Placing two nuts does not double the strength.

It wouldn't double the strength but properly equalizing two pieces facing the same direction does distribute the load which does increase their holding power as a unit. Neither piece is "stronger" per say but they are taking less load. I would think it would be almost twice the holding power.

It totally depends on the angle the sling forms. Best = two nuts vertically aligned (one directly above the other) connected in a way that shares the load e.g. sliding X. Ignoring friction, this would double the strength. At the other extreme, a pair of nuts widely spaced (sling's included angle >120 degrees) and you're looking at LESS THAN 4 kN strength for the setup.

KrisFiore wrote: It wouldn't double the strength but properly equalizing two pieces facing the same direction does distribute the load which does increase their holding power as a unit. Neither piece is "stronger" per say but they are taking less load. I would think it would be almost twice the holding power.

I was about to add to my reply above cause the question and my answer were a bit ambiguous. If placed and equalized one can increase the overall strength of the system but it is not just simply doubled. It depends on how the gear is placed. i.e. loading angles.

William Kramer wrote:Question spawned from cleaning gear after working a shift of calculating crazy drip rates and med dosage. If one places 2 DMM Peanuts (for example), each with a 4 kN rating, and uses them together with a sling or whatever as one piece of protection, is kN now simply doubled to 8kN? Seems too simple... I know I have read about this before on a forum here, but can't find it in the search. All I can find is about how to place opposing nuts in a horizontal, and doesn't ever mention the kN. I have always connected the 2 pieces with a sling that has a overhand and master point, like a mini 2 piece anchor, what other ways are there?

If you could get them perfectly equalized, so the load completely evenly distributes between the two of them, you could get 8 kN of strength. In practice, testing on anchors, has shown that nothing approaching perfect equalization ever happens -- you're likely to get something between 70/30 and 100/0 load distribution between the two pieces. So you'll likely get somewhere 4 kN and 5.7 kN actual load.

Gunkiemike wrote:It totally depends on the angle the sling forms. Best = two nuts vertically aligned (one directly above the other) connected in a way that shares the load e.g. sliding X. Ignoring friction, this would double the strength. At the other extreme, a pair of nuts widely spaced (sling's included angle >120 degrees) and you're looking at LESS THAN 4 kN strength for the setup.

thats the key. And like GunkieMike says, you've got to keep that angle down. The wider it gets the less it shares, to the point that eventually you're actually increasing load on each nut. I'd recommend keeping the angle pretty narrow. A lot of climbers don't realize that, especially when building anchors.

2 thing will throw a wrench in yr "calculations"

- the knot itself is not entirely predictable loading wise ... Thats the nature of knots

- the shorter leg of the sling will see more loading ... This is well documented in cordelettes

So in short dont worry about it ... 2 pieces add redundancy, but anything beyond some very basic load sharing i wouldnt worry about

;)

Dylan B. wrote: Isn't that because nylon cordalette is semi-dynamic? Wouldn't a fully static dyneema sling reduce or eliminate that (in theory, if not in practice)?

It should reduce it, whether it totally eliminates it is a different question

Of course you may well be using a nylon sling, nor can you predict the knot with much certainty ... Ie when yr "equalizing" two pieces on lead with a single hand do you tie the knot perfectly snug with absolutely equal tension on both sides?

Most folks likely dont unless its a big hands free stance

;)

Using a Sliding X to connect the two was mentioned earlier, would that better distribute the load between the two pieces, or would the shorter leg still get the brunt of it?

bearbreeder wrote:2 thing will throw a wrench in yr "calculations" - the knot itself is not entirely predictable loading wise ... Thats the nature of knots - the shorter leg of the sling will see more loading ... This is well documented in cordelettes So in short dont worry about it ... 2 pieces add redundancy, but anything beyond some very basic load sharing i wouldnt worry about ;)

Hence why just the sliding-x is the way to go when equalizing two small pieces. I'm guessing the lower piece would see a little more force, but in an almost inline system with a free sliding-x, it should be pretty darn equalized.
I've done this on thin crack climbs where I wanted to equalize a 00 and 000 cams to protect a runout and a crux. If you know you need it at a certain spot, you can pre-rig it with the right length sling and have it ready to go. Not that its all that hard to rig.

the sliding X MAY in theory distribute the load better ... however itll never truly be equal as the friction may "lock" the biner in place .... mistah titt (god i luv saying dat) has posted up quite a bit on this and his testing

the other problem with the sliding X is the possibility of "shock loading" if one piece pops (quite possible if yr equalizing 2 micros) ... whether that affects anything would depend i guess on how much rope you have out

personally i just place more pieces and clip them normally

;)

bearbreeder wrote:the sliding X MAY in theory distribute the load better ... however itll never truly be equal as the friction may "lock" the biner in place .... mistah titt (god i luv saying dat) has posted up quite a bit on this and his testing the other problem with the sliding X is the possibility of "shock loading" if one piece pops (quite possible if yr equalizing 2 micros) ... whether that affects anything would depend i guess on how much rope you have out personally i just place more pieces and clip them normally ;)

Good point, and definitely could be an issue. It's probably as equalized as you can get while actually climbing though, so worth knowing its an option.
A soft catch is probably the bigger factor you can affect that will be the least likely to pop a small piece.

The shock loading was my next question, thanks.

Something I've wondered about.

Two micronuts connected together with a sling tied with limiter knots as if you were making a sliding X. But, instead of making a sliding X, clip your rope carabiner into only one strand between the knots. This might eliminate the "clutch effect" of sliding X - which we know doesn't equalize anyway.

"But it's difficult to tie!"

True, but the OP claims he 'connected the 2 pieces with a sling that has a overhand and master point, like a mini 2 piece anchor' and that's difficult to tie, too. I suppose I could have it pre-tied.

"But it's only one strand! It's not redundant! Yer gonna die!"

Maybe. But, they're micronuts. If one blows, honestly, I'd expect them both to blow. I'm just trying to get a little more strength out of a marginal placement.

IDK. Just something I've thought about. Tell me why it's a badidea(tm).

wivanoff wrote: I'm just trying to get a little more strength out of a marginal placement.

Clip a Screamer.

Something to keep in mind when using the sliding x method, is that if one of the pieces does blow, even if the other holds, the sling will fully extend. Use with caution above ledges.

bearbreeder wrote:the sliding X MAY in theory distribute the load better ... however itll never truly be equal as the friction may "lock" the biner in place .... mistah titt (god i luv saying dat) has posted up quite a bit on this and his testing the other problem with the sliding X is the possibility of "shock loading" if one piece pops (quite possible if yr equalizing 2 micros) ... whether that affects anything would depend i guess on how much rope you have out personally i just place more pieces and clip them normally ;)

In most cases, I am inclined to agree with the idea of simply placing additional pieces and clipping them normally. Once in a while, though, I run into a situation where the nearest additional pieces are a long distance away and I want to get the most out of two shaky pieces. In this rare case, I usually choose a sliding X setup with limiting knots.

A couple of times now I have broken 3kN pieces even with a lot of rope out, so the OP raises a good question to consider. Thanks!

As a number of people have said, the chances that you will equalize the load with anything you can cobble together on a lead is virtually nil. Get two or more pieces in, sling so that the biners are at roughly the same level or connect draws or slings that are about the right length, and figure that's as good as its going to get. The theoretical discussions are fun, but friction in the the sliding systems and arm length plus knot variability in the fixed variations will probably overwhelm any theoretically optimal load distribution.

It is very hard to gauge the relative importance of so-called shock loading when a piece, rigged with a sliding X, pulls. As long as the amount of rope in the system is much larger than the extension after the piece fails, the effect on the remaining piece will be minor, meaning that it won't get much if any more of a load than if the failed piece hadn't been there at all, and may even get less if the extracted piece had enough resistance to allow rope stretch to absorb some fall energy. (Studies have shown that the rope snaps back when a piece fails and so some the fall energy absorbed by the failed piece is dissipated and the rope gets to start anew on the next piece down.)

Note, however, that this is very different than using a sliding X for belay rigging, when the total amount of rope available for energy absorption may well be comparable to the extension in the rigging, in which case extension can result in high fall-factors.

So I wouldn't worry about a sliding-X between two close protection pieces that aren't, say, immediately above the belay. Such rigging will not impose some inordinate load on a remaining piece if one of the pieces blows. The main advantage of the sliding-X for such situations is that it is quicker and easier to rig than anything involving knots, and if you are running out of gas, ease of installation could be the decisive factor in whether or not you actually test your system.

Perhaps it is worth emphasizing that you should try to get something bombproof and secure as close below the manky gear as you can manage. The "and secure" part refers to doubling carabiners and/or using lockers so that the rope can't come out of your "pro of last resort." When gear pulls, the rope can whip around in chaotic ways, and we have heard with surprise and sadness about even multiple detachments in such situations.

rgold wrote: (Studies have shown that the rope snaps back when a piece fails and so the fall energy absorbed by the failed piece is dissipated and the rope gets to start anew on the next piece down.) .

Hi, any chance of a link to those studies, please. I thought I'd read somewhere of some experiments a university did after a climber hit the ground in the USA which concluded the reason the second piece pulled was because the rope was semi-static by then.

David Coley wrote: Hi, any chance of a link to those studies, please. I thought I'd read somewhere of some experiments a university did after a climber hit the ground in the USA which concluded the reason the second piece pulled was because the rope was semi-static by then.

This is highly suspect just from a physics point of view. The condition of the rope (% elongation lost) would largely be dependent on the condition of the rope when the first piece pops and proximity of the next piece. If the next piece is 2 inches from the first, the rope won't have the same elongation properties if the next piece was 12 inches down.

Btw, agreeing with David, the post David quoted didn't carry over