Anchor Behavior When Pieces Fail

Folks often get backed into extreme positions by the nature of internet debate. The idea that theoretical "chalk board" calculations are of little practical relevance is just as wrong as the idea that these theoretical calculations model reality perfectly. Testing is subject to all kinds of design errors and confounding influences, to the extent that it may be impossible to decide on best practice without a good mathematical model to sort out the effects of various variables. On the other hand, basic mathematical models that have not been reworked in the light of test results may oversimplify so much that their results are only vaguely related to what one experiences in the field.

I think Atelis has already neatly summarized the current debate while avoiding the distracting irrelevancies. The fact of the matter is that we do not have good test data on the effects of extension in anchors. Moreover, it isn't even clear whether the participants in any discussion either have or agree on a clear definition of what is meant by an "effect." This problem is compounded by the fact that people continue to use the undefined term "shockload," sometimes in ways suggesting that there is something unusual and avoidable about it in the context of anchor loads.

If a load supported by three pieces is suddenly supported by only two, there will obviously be a sudden increase in the load experienced by the remaining anchors. Given that nobody knows what "shockload" means anyway, it would be perfectly reasonable to call this a shockload, in which case the failure of a piece will shockload an anchor whether or not there is any extension. So the effect of extension, if there is any, would have to be an increase in load beyond the shockload that is guaranteed by the failure of a piece in an analogous fixed-arm set-up. Our inability to standardize the "analogous fixed-arm set-up" makes for all kinds of issues with respect to testing.

It isn't going out on a limb at all to say that there are circumstances and configurations in which the effects of extension will be critical---really, this is beyond question. Although the confounding variables in real anchor situations are daunting, I believe that the crux of the matter boils down to the ratio of anchor extension to tie-in length, a fall factor for anchors. This is because, if the belayer is pulled off his or her stance, the only part of the system absorbing the belayer's fall energy is the tie-in, and the measure of the tie-in's ability to absorb fall energy is the same old H/L ratio, but now H is the amount of extension and L is the tie-in length. (A secondary but potentially serious problem occurs if the tie-in is made of low-stretch material.)

Definitive results may be a long time in coming. We have a little information about two-anchor equalizing systems, but almost nothing about three-anchor systems. In the meantime, climbers have to make anchor decisions, which are really carried out in a state of almost complete ignorance by people whose experience is acquired by building anchors that are never tested to evaluate the builder's judgments.

By far the best approach is to make sure that there won't be a fall directly onto the anchor, in which case most discussions like these become moot. But, at least in my experience, the potential for such a fall is present, if unlikely, most of the time, and so the building of very strong redundant anchors remains a consideration.

What to do in practice is still pretty much witchcraft. Or put another way, it's psychology, not physics. The thing that makes people feel best is what they do, in the absence of really effective guidelines. Like it or not, theoretical calculations are pretty much all we have to go on in this situation, and if they are not to be taken too literally, they at least provide an ingredient or two for the witch's brew.

It seems to me that if anchors are made of reasonably good pieces (remembering our fallibility in judging), then they should be viewed as distributed systems, not equalizing systems, and the speed and simplicity of fixed-arm rigging as opposed to dynamic equalizing systems makes the most sense for climbers doing climbs of any length. One of the many theoretical predictions that has been confirmed by experiments for fixed-arm rigging is that the piece on the shortest fixed strand gets the highest load, and so it makes sense to try to keep the anchor strands approximately the same effective length.

The "effective" modifier here has a purpose. The idea is that, first of all, the anchor rigging itself should be constructed from dynamic material, either 7mm cordelette or, as good if not better, the climbing rope itself. If a piece has a rigging arm that is significantly longer than the shortest arm, it should be extended with a low-stretch sling of some sort, thereby yielding an "effective dynamic arm" of shorter length. Such decisions can be made instantly, are easy to implement, do not involve the fiddling ultimately required by more complex systems, and seem as likely, given what we actually know, to distribute loads in a three-anchor system as well as can be expected, as long as the direction of loading agrees with the way the anchor was constructed.

If the anchor pieces are suspect, then equalization methods, in spite of our lack of knowledge about their behavior, may be a better option. The obvious solution to the three-anchor conundrum is to use four pieces equalized with a cascade of three sliding X's or, preferably, one of their modern lower-friction improvements. Then, having signed on for possible extension, one wants to tie in with as long a tie-in section of the climbing rope as is possible for the given stance. This will minimize the anchor fall-factor described above in case of a factor-2 fall, and so hopefully relegate the extension effect to the mythical status it now fallaciously enjoys for all configurations.

The trouble with all this is that "alpine" anchors are often suspect and building a four-piece monstrosity is mostly not an option for various reasons. So you live with more uncertainty, and do whatever makes you feel best. If an extending anchor is what is chosen, then the long tie-in for the belayer seems to me to be a sensible adaptation to the potential for extension.

Although this is pretty speculative, I think the best solution for alpine conditions, given our current ignorance, may be to build a two-piece anchor and with a third piece very close above, independent from the anchor, and used as protection for the leader. Equalette-type equalization for two pieces seems to be fairly effective, and three-piece systems may still deliver half the load to one of the pieces, making them perhaps no less resistant to some kind of failure, although of course more redundant. The extra redundancy in an alpine setting might well be trumped by the fact that the two-piece protected anchor is less likely---one would hope much less likely---to be subjected to a factor-2 load at all.

Rich Goldstone, Rockclimbing.com, 12/4/2009

Learning to Lead

There are really several learning issues involved. One of them is about adequate placements. Much of this can be learned as well or better in ground school, bounce testing with an aider.

Another excellent way, often recommended, is top-roped aid climbing. This allows the climber to bounce test every piece (remember to look away while actually bouncing!) It has the significant advantage that the leader learns just a bit about aid climbing and so will be much more able to get out of trouble. It is also likely to force the climber into finding placements when they don't have the ideal piece, which is a very good skill to have when actually leading. Moreover, you can play games like not allowing the largest stoppers so that nuts have to be placed sideways, or (for certain terrains) banning cams. The aspiring leader can also safely work with very small pro, which in spite of things often said can be important and effective on moderate routes. After the lead, simul-rapping with an experienced person to get commentary on the placements (and better alternatives) completes the process.

Ok, that handles placements, but doesn't deal with many other issues involved in leading. I can think of seven more offhand. Obviously, only the briefest of comments are possible here.

(1) Psychological issues: dealing with pressure and anxiety. Emotions tend to make people rush and skip essential placements or allow themselves to be satisfied with inadequate ones. One has to exert conscious control over natural stampeding tendencies.

(2) Clipping issues. You don't want carabiners loaded over an edge, so may have to thread slings in some cases. If something about the rock configuration looks like it might open a carabiner gate, use a locker or double up.

(3) Redundancy issues: knowing when to get in more than a single piece. Especially if you are a beginning leader, don't let some snotty light-is-right fanatic talk you into heading up with a minimal rack. When you sre learning and your judgement cannot possibly be very good, redundancy is your best bet for coming back in one piece. But you have to have the gear to do it, and you have to do it in a way that doesn't use up too much gear and doesn't create rope drag---see Item (4). Redundancy can apply to slings and draws as well. If a piece is truly mission-critical, consider clipping with two quickdraws with both sets of gates on opposite sides. Or carry a quickdraw or two with lockers on both sides and use that.

(4) Rope management issues: avoiding drag, guarding against nuts lifting. Sometimes you just can make a placement because it will create too much drag, but almost all the time the solution is long slings. One of the noticeable differences between experienced and inexperienced leaders is that you'll see an experienced leader climb down every now and then to lengthen a sling and so prevent drag from stopping them dead (double entendre intended) higher up.

I think unexpected zippering is the most common error experienced climbers make, so that means preventing it is especially hard to learn. Make sure a ground belayer is up against the wall and not standing back, but even so try to get in an early multi-directional piece. The idea sometimes floated that a cam in a vertical crack will rotate 180 degrees upward and hold is a dangerous fantasy you do not want to have tested---moving cams are even more unpredictable than stationary cams. Good directional pieces either need to be in horizontal cracks or else anchored down in some way.

Rope also has to be managed at belays so that it doesn't tangle and doesn't get hung up.

(5) Protecting the second. One of the weakest skills in the new leader's arsenal, but every now and then someone gets quite good and is still clueless in this regard (I'm sorry to say I've been on the receiving end of this type of incompetence far too often). The leader has a deep moral obligation to do everything possible to protect the second. The leader gets to choose the level of risk they want to confront, but the second is forced to endure the risk imposed by the leader. The leader has to go the extra mile, put in the extra effort, do whatever it takes to make sure their second is not going to take a swing with dangerous wall or ledge impact. If the leader has to make a long easy traverse (like walking across a ledge to a belay), the leader needs to build something on the order of a belay anchor over the second to make sure that pivot point is absolutely bombproof. I can't count the number of times I've seen this violated.

(6) Building a belay anchor. Plenty of stuff about this on the internet. Perhaps the main issue is doing it with all deliberate speed, because many climbers are maddeningly slow at this. (However, every climber, no matter how experienced, will sometimes require a lot of time to set up a trustworthy anchor).

(7) Retreat strategies when things aren't working out.

This is a hell of a lot more than just getting placements right, and much of it does have to be done in some practice leading situation---after the aspiring leader is already ok at placing gear in non-leading situations.

For advice on all this other stuff, by far the best set-up is an experienced climber jugging next to the leader. And close too, because you really want the experienced climber to be able to intervene. The aspiring leader temporarily clips into the jugs via a prearranged tether so that they can actually absorb what the jugging leader is saying. For instance, it isn't at all uncommon for the aspiring leader to miss, by a long shot, the best placement and make do with a marginal one. (This is especially true when the aspiring leader settles for a small cam when much better cam or nut placements can be made.) You want to be able to have them remove the crappy piece and place a better one. For at least part of that process, you'd really like to have them clipped in.

Ok, I know what everyone is thinking: no one has ever been taught this way. Not true, but perhaps nearly true, And yes, some of us learned all by ourselves, but some of the folks who went that route are dead or permanently incapacitated as a consequence, and you only hear how wonderful that method is from the ones who lucked out. Part of the reason why there are many more incompetent leaders out there (most of who have no idea of their own incompetence) than there needs to be is because folks aren't learning the full complement of necessary skills, thinking they're good to go once they can place gear that doesn't fall out as they climb past it.

BITD, people started leading and following easy climbs, and built their leading skills in parallel with their climbing skills. Gyms and, to an extent, sport climbing have completely undone that connection, and many climbers are "too good" to put in the time on easy climbs that would have allowed them to acquire items (1)--(7) safely and enjoyably. This means the kind of unlikely teaching scenario I described above is considerably more important now than it would have been many years ago. Good luck finding someone to do it for you, with or without pay!

I think a final comment is in order. Trad leading is risky, and risk is an integral part of the trad experience. Performing safely in the face of intrinsic dangers is what makes trad climbing trad, not what you are clipping into. I feel as if a lot of aspiring trad leaders don't get this, especially if they are coming over from gym or sport leading, which in most (but certainly not all!) cases is exciting top-roping. Folks like to pooh-pooh the old-fashioned "leader must not fall" commandment of bygone days, but almost all trad leads have sections, where the leader really must not fall. And other sections where the result is going to be very bad if some of the gear doesn't hold. Aspiring trad leaders need to know this and find the prospect attractive and exciting---they need to be going into the realm with their eyes wide open to the potential dangers. You don't have to do this. Make sure you know what you are taking on.

Rich Goldstone, mountainproject.com, 10/19/2014

Does Friction Matter?

According to David Custer in eb.mit.edu/custer/www/rocking/..., the coefficient of friction of aluminum against granite has been measured at 0.38. These students got 0.41 hypertextbook.com/facts/2005/g..., and The Valley Giant folks say 0.5 valleygiant.com/cam_math.html. If Mapeze is around, as a designer he probably has some values, especially for Euro limestone, where cams are known to be less reliable.

Obviously, the particular combination of aluminum against granite is not of great interest to researchers, so it isn’t easy to find values. But beyond that, the simple coefficient of friction concepts found in Amonton’s law are in fact the roughest of empirical estimates and are not any kind of natural law—people write PhD dissertations on friction; it is in fact an extremely complex and far from well-understood concept.

The concept is most applicable to contact between highly polished surfaces, in which the friction forces are primarily influenced by molecular interactions. Once the surfaces are physically irregular, all hell breaks loose because of the variety of ways the bumps and recesses can interact to produce resistance. I think that the almost universal practice of notching cam lobes is intended to leverage potential roughness interactions.

I think the message from research on the subject is that until you get up to loads of geological magnitude, the roughness of the surfaces matters far more than the materials, and so speaking as if there is a coefficient of friction between, say, granite and aluminum is far from illuminating.

When surface roughness and deformability matters, so does contact area, in which case one of the fundamental precepts of Amonton’s law is out the window. (Everyone knows more shoe rubber on the rock produces more adhesion, even though Amonton’s law would say not.)

Another important issue is the well-known disparity between static and sliding friction. Since cams often move when a fall happens, the applicable coefficient of friction may well be the lower sliding value rather than even a locally-measured static value. Then there is the fact, totally unrelated to friction, that a well-placed cam fails not because frictional forces are insufficient to hold it in, but because of shear yield stresses on the aluminum lobe material. In such cases there will be evident gouging of the cam and it may be possible to find aluminum deposited on the crack walls. (I've seen the aluminum left behind in testing jigs but not in real rock.)

Given that Amonton’s law may be a poor description of what happens between a cam lobe and crack wall, I think it is something of a miracle that cams designed in accordance with that law work anywhere near as well as they do.

Rich Goldstone, mountainproject.com, 2/14/2015