Discussion Topic |
|
This thread has been locked |
bobh
climber
Bishop, California
|
|
|
Jan 25, 2007 - 12:34pm PT
|
The potential for minor-axis loading of the power point biner in the anchor pictured above is something that should really be avoided. As pictured, this is a bad rig. Additionally, both this anchor and the mooselette anchor reduce extension at the expense of putting some 'american-triangle' type force amplification on the lateral anchor points. Something to consider when tabulating the pros and cons of each system.
Interesting discussion. Love your anchor books, John.
|
|
Ksolem
Trad climber
LA, Ca
|
|
|
Jan 25, 2007 - 01:03pm PT
|
This is an interesting discussion with some good examples as well. But, practical application in the field is another story. So I have a question or two for all of you anchor scientists.
First, how often, when you set an anchor system at the end of a pitch, do you really think there is a possibility that one or more of your pieces might pull if loaded?
Also, given the fact that there is a limit to how much stuff one wants or is able to carry up a hard pitch, what would you rather have when you arrive at the belay - 20 ft. of 7mm cord and 6 or 8 extra carabiners, or a couple extra cams and nuts to choose from.. ?
Not to say that equalization is not important, especially if you are in the unfortunate position of having a dicey anchor. But I usually look at the multiple pieces in an anchor as backups. I use the rope to clip in, usually in series without any slack between. Of course I am usually swinging leads, not guiding, so this is not inconvenient. And with only 35 years of this under my belt I guess I am due to get chopped any day now anyway... :-)
|
|
rgold
Trad climber
Poughkeepsie, NY
|
|
|
Jan 25, 2007 - 02:07pm PT
|
Ksolem, I do something similar much of the time, and it wouldn't be surprising to find JL did too. I've never had a piece pop on a loaded anchor, but I do know people who have and have read about others.
But regardless of whether or not it seems likely that gear will fail, perhaps you might change over to something that didn't load your anchor pieces sequentially with the full load if the new method was almost as quick and easy as your series of clove hitches and didn't eat up a good part of your rack for two belays.
Moreover, for better or worse, climbing is heading in the direction of "foolproof" systems that enable people who have not acquired experience through a long apprenticeship to participate. Direct rope tie-ins were replaced by swami belts which where, in turn, replaced by harnesses, which have now been replaced by harness with buckles that don't need to be back-threaded. Belay devices have been followed by autolocking belay devices, nuts by cams, and so on.
Traditionalists scream "foul" when innovations appear, but then, after a sufficient period of abstinence, embrace them. Gear that make things safer for novices typically has found favor with experts. The same thing will happen with rigging systems, if we can together come up with better ways of doing it.
|
|
Ksolem
Trad climber
LA, Ca
|
|
|
Jan 25, 2007 - 02:25pm PT
|
RGold - I don't disagree, and I am not one to cry foul over new innovations.
How about the second question..?
|
|
murcy
climber
San Fran Cisco
|
|
|
Jan 25, 2007 - 03:16pm PT
|
given that the alternative is a bunch of biners and too much fussing, why not have a special piece of gear, a "powerpoint biner", with a main locking compartment for the load and three little closed compartments (maybe with pulleys on them like those dmm revolver biners) for cordalette loops. keep a single, continuous cordalette loop running through all three pulley compartments. clip the three resulting loops of it to your pieces (shortening the cordalette with a butterfly if you like). that's as good equalization as you're going to get and it's instantaneous to set up because you'd keep it pre-tied.
for limiting extension have a bundle of three short "backup" cords with a figure 8 on a bight tied at their mutual end; the bight is kept clipped to (or tied through another special compartment of) the "powerpoint biner". tie the cords off loosely to each piece based on how much extension you want to tolerate.
one big specialty biner, one cordalette that can be a bit shorter than usual (no huge figure 8), one bundle of three cords that's about half a cordalette total in weight. compared to the old cordalette method, a bit heavier, but just about as easy to set up.
i don't know how important this stuff is compared to solid placements and just not screwing up etc., but it is a fun brain teaser.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jan 25, 2007 - 03:35pm PT
|
maybe I can answer as a scientist...
This is an interesting discussion with some good examples as well. But, practical application in the field is another story. So I have a question or two for all of you anchor scientists.
Practical applications is what we all are trying to get at, if the problem is susceptable to meaningful analysis, then that is a good place to start as it will make the principals important to a successful application apparent.
First, how often, when you set an anchor system at the end of a pitch, do you really think there is a possibility that one or more of your pieces might pull if loaded?
You never know, and experience isn't necessarily the answer. There is a finite probability that your anchors will blow. We do not know what that probability is, however, you cannot calculate a meaningful answer by taking the number of anchors you've set and saying "less than one in N" as this implies that the chance of failure goes down everytime you set an anchor that doesn't fail.
This is the "Challenger" mind set that NASA had, they couldn't calculate the probability of catastrophic failure that made sense, so they set a limit on the number of flights. The reason the calcuation didn't make sense is that they hadn't had a failure in the time they would expect, 1/200 flights... Now we know that is about the correct failure rate.
Same thing with anchors, you don't know if a particular anchor you set would or would not have failed, you never tested it. You don't know how close you've gotten to disaster 'cause the disaster never occured.
Also, given the fact that there is a limit to how much stuff one wants or is able to carry up a hard pitch, what would you rather have when you arrive at the belay - 20 ft. of 7mm cord and 6 or 8 extra carabiners, or a couple extra cams and nuts to choose from.. ?
I think that the initial "concept demonstration" is where we'd like to get to first, then the technology can be refined from there. The cordelette's appeal was the simplicity of setting it up. The cordelette replaced numerous slings, etc, in systems that equalized. If there is a solution to the problem, I'd think it unlikely that the first thing proposed is the ultimate thing we use.
Not to say that equalization is not important, especially if you are in the unfortunate position of having a dicey anchor. But I usually look at the multiple pieces in an anchor as backups. I use the rope to clip in, usually in series without any slack between. Of course I am usually swinging leads, not guiding, so this is not inconvenient. And with only 35 years of this under my belt I guess I am due to get chopped any day now anyway... :-)
We know that equalization is desirable, and we know that it works because it has been used in aid placements as well as to protect leaders, in both cases where a single piece may not hold. The anchor system works best when the load is as distributed over as many pieces as practical, thus no one component is stressed. This is a simple engineering design rule, stay far from the failure point as possible in a multiply redundant system where any one of the redundancies would accomplish the goal of the system.
As for when you will get the chop, the probability of it happening is probably no differnt today as it was 30 years ago... at least not in terms of the knowledge you bring to the table.
Sometimes you roll the dice and you win... fortunately the dice is loaded in your favor, but it is still possible that the dice roll could go against you. We all should keep trying to load them even more in our favor.
That's what this conversation is all about.
|
|
GOclimb
Trad climber
Boston, MA
|
|
|
Jan 25, 2007 - 03:59pm PT
|
Ksolem - the only reason to be concerned with any of this is if there is a possibility of the leader falling onto the belay. For normal lead falls and for bringing up a second I've been perfectly happy with just wedging my fat ass in a crevice, or backing up my two good legs with one really good nut. For that purpose - sure, a few good cloved pieces is perfect.
But this is really all to answer the question of what happens when the leader falls with no gear in.
Or to put it another way - how many of your clove-hitched-in-sequence anchors would you have been comfortable with catching a leader with no gear on the pitch?
Leader is 10 feet up, falls to 10 feet below you, your bottom piece is weighted with a pretty high force - depending on the type of device you're using, perhaps 10-15kN. Can that one bottom piece hold all that force? What if it pops? Then the next piece in sequence feels approximately the same force. You get the idea.
GO
|
|
rgold
Trad climber
Poughkeepsie, NY
|
|
|
Jan 25, 2007 - 05:04pm PT
|
How about the second question..?
I think that an appropriate anchoring system would make it a false dichotomy. But I also agree with you that systems that eat up too much gear are not going to be useful to many climbers.
On the other hand, climbers have, over time, shown almost limitless willingness to carry more gear. The common rack I see nowadays has at least twice as many pieces on it as the rack of nuts we used 30 years ago, and the pieces, cams, are heavier too. I could go on about the other "necessities" climbers now have on their harness that add weight to the enterprise, starting, I suppose, with the harness itself.
So an alternate answer to your question is, if the rigging system is effective enough, climbers will carry it and the extra gear they think they need even if the load is heavier.
|
|
the Fet
Knackered climber
A bivy sack in the secret campground
|
|
|
Jan 25, 2007 - 05:51pm PT
|
In my limited knowledge, I understand the dynamic properties of the rope should limit the max force(in a factor 2 fall) to not more than 12kN, and is about 9kN.
However, if you are using a re-direct at the belay which acts as a pulley you could almost double that force on the biner/anchor to 18kN.
A camalot is rated for 8 - 14 kN.
A closed biner is rated for about 24 kN.
Personally, I think that it's calling it close to fully rely on an anchor without any form of equalization. Say you have a 9kN leader fall on a 14kN camalot, that's a saftey factor of about 1.5 (14kN / 9 kN). And it gets worse if you use a small camalot or a redirect where you could break a piece, or pop it.
Equalizing 2 pieces (with a sliding X with limiter knots, or an equalette) should do a pretty good job at sharing the force. So your almost cutting the force on each piece in half and doubling your safety factor, very easily. So an approximate 50% reduction on the force compared to just 1 piece.
Equalizing 3 pieces is more difficult, time consuming, and probably requires more gear, and you're only getting another possible 17% reduction of force on each piece. (i.e. instead of 50/50 you get 33/33/33. So there's a diminishing return the more pieces you equalize.
For the average trad anchor where the pieces appear solid, I think splitting the force among 2 pieces is probably going to do the job fine (with a 3rd as a backup as needed). You would probably only need to equalize 3 pieces if they weren't solid placements. Then you would probably be an advanced climber and have more options in your bag of tricks for that situation.
So as a replacement for the cordelette, and as the anchor 90% of climbers could use 90% of the time, I think something that equalizes two pieces, simply, with little gear is the way to go.
I'm not giving up on a solution to something simple, that will equalize 3 pieces with minimum gear, but I don't think it's really necessary for most people and situations. And due to the complexity I don't know if there is a simple solution.
A couple points (that have been addressed before but the numbers above reinforce):
*Always tie in with the rope
*A belay redirect should be used judiciously
*Trusting one piece with your life ain't a good idea
*Place a piece above the belay asap
|
|
Mighty Hiker
Social climber
Vancouver, B.C.
|
|
|
Jan 25, 2007 - 06:19pm PT
|
A fascinating discussion, with lots of interesting stuff. I know just enough physics to get the idea, though analysis of dynamic systems is pretty complex.
I'm still not sure what the objective is, or more accurately how equalizing anchors will contribute to it. If the goal is to better understand belay system dynamics, so that climbers learn to build stronger/safer belays, that's good. I suspect that there are other factors that have a greater influence on this, including equipment and environment limitations, and the subjective elements - skill, experience, circumstances.
Looking at it another way, an analysis of climbing accidents may show belay failure well down the list, and that when it does occur, it's more commonly due to inadequate or poorly placed gear, poor rock, and/or the subjective factors. Should we perhaps be looking at those?
More worrisome, a discussion like this can easily lead to some concluding that the solution is fixed anchors - bolts - at all belays. Which in turn can lead to greater evils, such as the grid bolting found in some places, even though the rock offers good natural protection. Those who think that climbing can or should be completely safe are an ever-present risk.
Somewhere I once heard or read that the human body in a sit harness will likely suffer internal injuries or worse if subject to forces of over 12 kN. Hence gear being designed to take roughly twice that force.
|
|
NoRushNoMore
climber
|
|
|
Jan 25, 2007 - 08:12pm PT
|
Assumptions about FF2 load of 12-18kN on the anchor are unrealistic. Even gri-gri slips at about 4.5kN giving max force in the case of belay thru the anchor of about 7.2 kN
And that is only in if you are anchored down. Otherwise you will be sucked into power point and in to the same load position as if you belaying of the hardness: 4.5kN max load on the anchor.
With these numbers in hand whole discussion about load balancing is a waste, all you need is redundancy (any other belay device will give you even lesser numbers to worry about)
Of course there is a case of human funk device but that much you can control instead of overbuilding anchor
|
|
Largo
Sport climber
Venice, Ca
|
|
|
Jan 25, 2007 - 09:20pm PT
|
Ya' all:
Don't want to speak too soon but I will anyhow. Im perilously close to figuring out the equalized 3-point anchor set up (rigged on one standard piece of thin cordage with no shenanagans or gizmos). Gotta few bugs to work out so it may take a few more hours but I'm hoping . . .
This is fun because I always enjoyed physical puzzles.
JL
|
|
cintune
climber
Penn's Woods
|
|
|
Jan 25, 2007 - 10:01pm PT
|
Well, JL, that will deserve a fresh page, so let me do the honors of filling this one out.
|
|
john hansen
climber
|
|
|
Jan 25, 2007 - 11:03pm PT
|
I brought up the idea before for a more springy cordellete that would stretch more and distribute the load. As the first anchor point began to come under load, it would only take a small percentage of the total load before the second piece started sharing the load. As both these "arms" stretched further the third anchor point would also start to come under load.
I know this is more of a force 'distribution' rather then true equalization.
Does this idea make any sense Ed ,and all you other number crunchers on the topo.
And here is another probably stupid idea. Imagine a V shaped piece of fabric about two feet tall and eighteen inces across the top made out of something like they use for trampolines.
At the bottom of the V would be the power point. On top of the 'V' would be a 'W' of three adjustable clip ins. This way as the power point was loaded it would have the same affect as the system above, only greatly enhanced.
Imagine a one pound wieght,connected by three wire cables to three nails driven into the wall so the cables are as close to equal as the eye could see. You drop the wieght ,and one of the anchors will be 'shock loaded' with the full force generaterd by the fall. What would a scale measure that force as...
Now , imagine the same set up only with rubber bands instead of cables. As one slowly comes under load the other points would gradually take a share of the force generated.
Does this make any sense or am I just full of Stienlager?
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jan 26, 2007 - 12:43am PT
|
the impact force grows, at worst, with the square root of the spring constant... for falls that generate much more force than the weight of the climber.
So if you reduce the spring constant by a factor of 4, you will get, at most, a factor of 2 reduction of the force.
If you look at the ST Forum topic physical properties of ropes and slings I reported on several types of ropes and slings:
K = 11.2 kN for a Beal dynamic rope,
K = 24 kN for nylon webbing
K = 30 kN for a 7mm perlon cord
K = 109 kN for a 5mm spectra cord
Using a 7mm perlon cord would provide a smaller impact force than a 5mm spectra cord... by a factor of 1.9 (nearly 2), depending on the magnitude of the fall. For small falls the difference will be smaller.
In my analysis higher up on this thread, the spring constant K of the slingage is a part of the calculation.
|
|
rgold
Trad climber
Poughkeepsie, NY
|
|
|
Jan 26, 2007 - 10:36am PT
|
I brought up the idea before for a more springy cordellete that would stretch more and distribute the load. ...I know this is more of a force 'distribution' rather then true equalization. Does this idea make any sense Ed ,and all you other number crunchers on the topo.
How stretchy do you have in mind? The belayer might be a bit miffed if it turns out he's in for a day of bungee jumping.
More seriously, there appear to be two obstructions to load equalization. One comes from the inevitable practical failure to have the arms exactly the correct length in knotted rigging. Wootles' results illustrate that the resulting inequities can be quite significant. It has been hypothesized that stretchier material will offset unequal arm tensions in this situation. Just how elastic the rigging needs to be before one sees a significant equalizing effect is unknown.
The second obstruction to load equalization comes from unequal arm length. Changing the stretchiness of the rigging might reduce the total load but can make no difference at all in inequities of distribution in this case, so stretchier rigging material cannot provide a comprehensive solution to the equalization challenge.
I don't think one ought to view the anchor rigging itself as part of the fall energy absorbing system, and I don't think one is likely to get much contribution from any standard rigging. Part of the reason is the load is supported not by one strand of the material in a cordelette rig but rather by six, so the anchor is going to be a relatively rigid component of the system.
|
|
Largo
Sport climber
Venice, Ca
|
|
|
Jan 26, 2007 - 10:48am PT
|
Rich wrote: "I don't think one ought to view the anchor rigging itself as part of the fall energy absorbing system, and I don't think one is likely to get much contribution from any standard rigging. Part of the reason is the load is supported not by one strand of the material in a cordelette rig but rather by six, so the anchor is going to be a relatively rigid component of the system."
I suspect that a workable soultion is kind of polymer biner, or doughnut, that we can attatch and tie into at the power point (backed up by a sling, of course). Modern polymers are remarbably strong, and the relative stretch can be controlled in fabrication. This is a possibility worth investigating. A four inch polymer "power ring" that might stretch to, say six or eight inches under extreme loading might bear some interesting results providing it's light and sufficiently durable.
JL
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jan 26, 2007 - 11:08am PT
|
one way to play this game is to take the extremes,
the stretchiest material will have a K = 0 kN,
then the impact force will be: F = 2 mg
twice the weight of the climber.
If the K -> very big,
F ~ mg*sqrt(2*f*K/(mg))
where f is the fall factor = h/L the distance of the fall h divided by the length of rope L.
Now here's a thought and a jump into complexity... you could have multiple polymer rings, each with a different K, in colors, and build a cordelette anchor attached through the rings to the anchors. For short arms you'd put a strechier ring, for long arms a stiffer ring (or no ring).
That would equalize the force...
|
|
cintune
climber
Penn's Woods
|
|
|
Jan 26, 2007 - 11:55am PT
|
The problem I see is that whatever stretches will bounce back, and the bigger the load, the more often, and the bigger potential variation in the angle of pull. This repeated loading and unloading of a "bungeelette" might defeat the purpose with sketchy anchors by walking them right out of their placements. Although I'm starting to sound like a broken record by now, this is the beauty of the screamer. Peak load is limited to ~2Kn, and there's no rebound to add to the uncertainty.
|
|
Brian in SLC
Social climber
Salt Lake City, UT
|
|
|
Jan 26, 2007 - 12:24pm PT
|
I suspect that a workable soultion is kind of polymer biner, or doughnut, that we can attatch and tie into at the power point (backed up by a sling, of course). Modern polymers are remarbably strong, and the relative stretch can be controlled in fabrication. This is a possibility worth investigating. A four inch polymer "power ring" that might stretch to, say six or eight inches under extreme loading might bear some interesting results providing it's light and sufficiently durable.
Hmmm, like a dog chew toy (or the donut ring and chew toy that some folks use to train hand strength with).
Interesting...heck, this might be KISS off the shelf easily available...
Someone oughta go to the pet or grocery store, pick one up and load test it...high loading rate, see the peak load graph type thing.
-Brian in SLC
|
|
|
SuperTopo on the Web
|
Let us know!