By Mark Nelson
From Coniferous, CO
Dec 18, 2007
| brenta wrote: I think this study is flawed in many respects.
My impression of this study was that they show destructive testing of the anchor based on a certain type of rigging. I can't provide a direct answer to your concerns.
I think one of the points they brought out about angles was surprising to me. I think they were going after: If you had the choice between good placements & marginal angles OR good angles & marginal placements; choose the good placements.
In review of this thread, we discussed a little bit about the material used in a no-extension rig. I would agree with this report that by using elastic rigging, it will react better to manage the energy than by using high-strength dyneema/spectra as the main rigging.
I disagree with their quick summary of sliding x rigs. It's easy to make this rig both redundant and limited extension. Stricker had offered the thought of the possibility of biner cross loading in a sliding x (I can't remember the thread topic); but I can't see it unless the angles are just so pronounced -- I can see friction being a problem, which is why sling redundancy should be a part of this rigging.
As to why use cord. It's just one tool for redundancy -- I think this report does show it can be relied upon for recreational climbing within a redundant system. If the climber's have just one leader and/or multiple seconds; this rig offers workable tie-in points for climbers, equipment, & packs. You can also use cord for decent anchors/v-threads, buddy evac, self ascension, & probably other applications I can think of if I had some more time.
Can't you use slings also? sure; but I'd like to keep slings for leading. And, what about leading ice, most of which climbers have screamers; cord would be a real nice thing to have.
Can't you just use the rope? sure, if swinging leads, this is the ticket. I don't think anyone has really disputed the value of the climbing rope as anchor rigging.
Overall, the main point I think with these findings is to look at whether or not cord will serve adequately to make a redundant anchor; I feel okay with what they found. |  |
By brenta
From Boulder, CO
Dec 18, 2007
| Mark Nelson wrote: My impression of this study was that they show destructive testing of the anchor based on a certain type of rigging.
There was a bit of destructive testing, but mostly it was not. In the main tests, they pulled only until the main load cell read 20 kN. If you look at the bar charts, you will see how most bars in the rightmost groups extend to exactly 20 kN.
They also pulled until they broke the cord in the experiments of Figure 20, but that's only a small part of what they did, and effectively confirmed that 7 mm cord doubled up and passed through a biner will start breaking at a bit less than twice its rated strength.
Mark Nelson wrote: If you had the choice between good placements & marginal angles OR good angles & marginal placements; choose the good placements.
In a way, it's hard to argue with this. A marginal placement may hold close to nothing. At least, with angles, you know what you are getting into. My gripe with this conclusion of theirs is that they fail to mention that widening the angle in a three-point anchor puts most of the stress on the middle piece. Granted, it is better than in a two-piece anchor, where the forces may exceed that in a one-piece anchor, but there's still a considerable incentive to keep the angle small.
Mark Nelson wrote: I would agree with this report that by using elastic rigging, it will react better to manage the energy than by using high-strength dyneema/spectra as the main rigging.
It stands to reason, though this report does not contribute new evidence.
Mark Nelson wrote: Overall, the main point I think with these findings is to look at whether or not cord will serve adequately to make a redundant anchor; I feel okay with what they found.
Yes, I would agree that 7 mm cord can be used to build safe anchors. | |
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