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dadvntur
Feb 12, 2010, 3:34 AM
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Assuming a solid ice column, solidly attached at both top & bottom, what would the minimum diameter of the column need to be before one would begin to seriously consider slinging it for use as natural protection on a lead climb? [such as example shown in figure 19-5 in "FOH"].
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rock_fencer
Feb 12, 2010, 3:40 AM
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People rap off V-threads made by boring 2 holes at an angle such that they form a V with an ice screw. I dont ice climb but i think a midrange to long screw is used so around 16-20 cm sides of the triangle. you can do the math from there
i dont ice climb though so i have no idea what im talking about
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builttospill
Feb 12, 2010, 3:57 AM
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I've slung a tiny column (really just a hole in a curtain) the size of my wrist before. Sure as hell wouldn't want to take a fall on it though.
Not sure.....the V threads are made for rappel anchors, not lead falls, but the point still stands to some degree. Maybe someone has done some testing on this? A screamer would certainly be well utilized in these situations.
A lot of it will be situational of course as well, with respect to the quality of the ice. This is an interesting question though....would be nice to have a ballpark answer.
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brokesomeribs
Feb 12, 2010, 4:27 AM
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I have ZERO empirical data, but I generally figure that it's only worth stopping and wasting energy if it's at least bicep sized (5"-6" diameter). Absolutely getting a screamer. Don't fall on it.
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tomtom
Feb 12, 2010, 8:23 PM
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I doubt anyone has ever tested this systematically, so your guess is as good as anyone else.
When in doubt, don't fall.
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dadvntur
Feb 13, 2010, 3:31 AM
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Thanks for responses. I guess I should have been clearer that I wasn't expecting empirical study results, I was just wondering what the opinions were of others as far as where their minimum threshold for reasonable safety was.
The only two ice climbing sources I have ["FOH" 7th Ed. & W. Gadd's "Ice & Mixed Climbing"] simply state that, "Runners can be placed around small ice columns." Neither giving any suggestion of diameter beyond "small". Although Gadd's book does elaborate a bit more on threading curtains, stating "Some curtains can also be punched out and threaded. A 6-inch curtain is very strong..."
I had the opportunity to thread a solid but small 7 inch diameter column recently, which was seperated by a gap from a small curtain (both about 3 feet tall, solidly attached top & bottom). Reaching through the gap with one arm/hand opposed to other hand held on other side I guessed the curtain to be about 8 inches thick. The column diameter didn't inspire any confidence in me - but I'm a new leader. Anyway it was a short route (45' or 50'), so I had plenty enough screws, so I just sunk a screw in the adjacent curtain and moved on. I'm guessing that if the column was a foot in diameter I probably would have been more inclined to sling it.
(This post was edited by dadvntur on Feb 13, 2010, 3:33 AM)
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rangerrob
Feb 15, 2010, 6:16 PM
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Most of these things are placed not so much for the lead fall protection, but for the fact that it is there to downclimb to if you need to and hang on it. I've never seen anyone fall on a small diamter slung column, nor would I want to. Just to give yourself a rough idea of the weight these things will hold, hook your tool around some varying size ones while on TR and jump up and down on it. You'd be surprised by how little of a piece of ice will hold your body weight. Now consider that a sling will probably spread the force across more of an area than the pick of your tool does, and it gets even better. The fact that it is there to come back to is the key..not that it is there to fall on.
When recently asked how his season was going, a friend of mine replied "I am building up an impressive list of routes I have bailed off of" That's what I mean.
RR
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gunkiemike
Feb 16, 2010, 1:26 PM
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2 in diameter = purely to redirect the rope. 3-4 in = psychological pro. 5-6 in = might hold a short slide. 7-8 or more = I'd trust it.
But I have never tested these rules-of-thumb. It's just my mental model.
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CamCactus
Feb 16, 2010, 1:36 PM
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First post, created an account to answer this, long term follower of RC. English is my 2ond so bear with me.
My recommendation is to try it. Fun and painful. I have tried it on two "ice-pillars".
I was 12 meters up and my tie-in knot was 2 meters above the clipped carabiner. FF~ 0,33. I weigh 80 kg, and the belayer weighs 80 kg. I used a 10,5mm Mammut rope, old and bad dynamic properties. The ice was around 3 weeks old, the temp -1 C (no big changes in a week). I put a 8mm sling around an icicle (? spelling, small "ice-pillar") 30 cm high (length of a forearm) with solid rock-attachment at the top and fat ice at the bottom. At the thinnest point it was the width of a big wrist. I had clipped a screamer to the sling (Petzl, starts to rip at 2 kN). It did not hold the fall. The screamer did not start to rip. I barely felt a thug as it broke.
The other icicle was just next to the first one. 0,5-1 meter high and the width of a thigh. Same setup, but no screamer. (For you nerds, yes I had a longer sling to create the aprox same FF) It held the fall. You never know but it "acted" solid.
I could have tried more, but hell was I beat up. Needless to say I had a top-rope and a separate belayer as a backup.
On a side-note, I don´t think you count on that an icicle with the diameter of 20 cm (aprox diameter of a v-thread made with 22cm screws) to have the same holding power as a v-thread. The v-thread "engages" the ice surrounding it. So it´s not only the ice within the 20 cm diameter that holds the v-thread. Thus the v-thread is stronger than a 20 cm icicle.
That´s what I believe, I have nothing to support that assumption.
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angry
Feb 16, 2010, 2:38 PM
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Cool!! Sounds fun.
Did you just batman up the tr until you were in place to take that whipper without tool or crampons?
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CamCactus
Feb 16, 2010, 2:57 PM
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angry wrote: Did you just batman up the tr until you were in place to take that whipper without tool or crampons?
I was not high of the ground. After I made the small platform from where I jumped, I tossed the axes and crampons down to the snow.
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shoo
Feb 16, 2010, 3:28 PM
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I'm also pretty curious about this. Any experts out there?
I think that this is missing a lot of critical information here. A couple of thoughts below. Could be wrong. Who knows.
The first thing I would be looking at is how close the top and the bottom of the icicle are to where you are slinging it. Icicles that are bonded to rock or other ice more closely will almost certainly be MUCH stronger. I would also be looking at how the top and bottom of the icicle are bonded.
The quality of the ice is also obviously key. A rotten pillar isn't going to hold much. On the other end, a perfectly clear icicle might also be weak against pulling outward, since its fracture lines are horizontal.
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dynosore
Feb 16, 2010, 3:43 PM
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Ice has a tensile strength of around 1 MPA, and a fracture toughness of about 0.1 MPA. Ice will suffer brittle failure under sudden loads like a fall. What does this all mean?
1 megapascal = ~145PSI. So, backcalculating for the diameter of a column of perfect ice that would hold 1000lbs force (4.5kN):
pi*r^2*145 = 1000
r = 1.5, so D = 3.
A 3" diameter, bombproof ice column attached at both ends could in theory hold a 4.5 kN fall. However, ice in nature is never perfect. Imperfections could bring us more into the region of fracture toughness, so that ice column might only hold 0.5 kN if it's full of cracks and imperfections.
Conclusion: calculations are fun, but only experience can tell you how solid an ice column is going to be, as strength for a given diameter could vary by a factor of 10 or more. Anything less than 3" in diameter is a pretty, useless feature.
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verticon
Feb 17, 2010, 6:36 PM
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I found some data about ice column strength in a french study (a PDF named "cascades de glace") but I can't upload it because it's larger than the 150 kB limit.
Here are the numbers:
Cross sect. Height Breaking strenght
cm2 - h (cm) - daN - daN/cm2
20 - 12 - 210 - 10,7
50 - 20 - 385 - 7,7
176 - 60 - 1225 - 6,9
315 - 20 - 700 - 2,2
(This post was edited by verticon on Feb 17, 2010, 6:38 PM)
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dadvntur
Feb 18, 2010, 3:24 AM
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I was just expecting rules of thumb like 'Gunkiemike' posted. But this French study 'Verticon' posted is interesting.
'Verticon' - could you elaborate on the definitions and applications of the 4 columns of data you posted? Specifically:
Does the 'cm2' cross section mean the diameter of the column squared? So the diameter is the square root of that number?
The height is straight forward, but what is 'daN', and how would 'daN' translate to "kN" force?
And finally, could you explain the significance/application of the final 'daN/cm2' column in lay terms?
Thanks.
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verticon
Feb 18, 2010, 8:25 AM
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For the first example, the cross section is a circle, so, for a cross section of 20 cm2, the radius is 2.52 cm (~1 inch). The column is 12 cm heigh (~5")and it will break at 210 daN (2.1 kN), which divided by 20 cm2 (area of the cross section) gives 10.7 daN/cm2 which is the tensile strength.
The same maths for example 2 and 4, but for #3 the cross section is oval and it's loaded along the bigger dimension, which, althought the column is 60 cm high (~2') translates in a bigger strength: 1225 daN (12.25 kN).
The interesting part is that the tensile strength is not linear, but it's affected by the size and shape of the cross section.
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altelis
Feb 18, 2010, 2:19 PM
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verticon wrote: For the first example, the cross section is a circle, so, for a cross section of 20 cm2, the radius is 2.52 cm (~1 inch). The column is 12 cm heigh (~5")and it will break at 210 daN (2.1 kN), which divided by 20 cm2 (area of the cross section) gives 10.7 daN/cm2 which is the tensile strength. The same maths for example 2 and 4, but for #3 the cross section is oval and it's loaded along the bigger dimension, which, althought the column is 60 cm high (~2') translates in a bigger strength: 1225 daN (12.25 kN). The interesting part is that the tensile strength is not linear, but it's affected by the size and shape of the cross section.
Not too surprising, eh? They ARE scientists...I mean circles. They ARE circles...
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verticon
Feb 18, 2010, 3:21 PM
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altelis wrote: verticon wrote: For the first example, the cross section is a circle, so, for a cross section of 20 cm2, the radius is 2.52 cm (~1 inch). The column is 12 cm heigh (~5")and it will break at 210 daN (2.1 kN), which divided by 20 cm2 (area of the cross section) gives 10.7 daN/cm2 which is the tensile strength. The same maths for example 2 and 4, but for #3 the cross section is oval and it's loaded along the bigger dimension, which, althought the column is 60 cm high (~2') translates in a bigger strength: 1225 daN (12.25 kN). The interesting part is that the tensile strength is not linear, but it's affected by the size and shape of the cross section.Not too surprising, eh? They ARE scientists...I mean circles. They ARE circles...
Yeah, I mean "the tensile strength it's not constant", my mistake.
Now that you know what I'm talking about, would you explain what are YOU talking about ?!
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altelis
Feb 18, 2010, 3:44 PM
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verticon wrote: altelis wrote: verticon wrote: For the first example, the cross section is a circle, so, for a cross section of 20 cm2, the radius is 2.52 cm (~1 inch). The column is 12 cm heigh (~5")and it will break at 210 daN (2.1 kN), which divided by 20 cm2 (area of the cross section) gives 10.7 daN/cm2 which is the tensile strength. The same maths for example 2 and 4, but for #3 the cross section is oval and it's loaded along the bigger dimension, which, althought the column is 60 cm high (~2') translates in a bigger strength: 1225 daN (12.25 kN). The interesting part is that the tensile strength is not linear, but it's affected by the size and shape of the cross section.Not too surprising, eh? They ARE scientists...I mean circles. They ARE circles... Yeah, I mean "the tensile strength it's not constant", my mistake. Now that you know what I'm talking about, would you explain what are YOU talking about ?!
What I'm talking about with regards to the linearity or to the scientist? If you don't get the scientists references....well you aren't a Dave Chappelle fan!
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dadvntur
Feb 19, 2010, 3:55 AM
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I'm hung up on the "cross section" and "cm2" column definitions. Are they an area or the circumference?
If it's circumference, then I can get the diameter of the three circular test ices you listed by the formula: radius = circumference/2(Pi); then multiplying the radius times 2 to get diameter. [That yields diameters in inches of 2.48" (line # 1), 6.2" (line # 2), and 39.1" (line #4).] But I'm guessing 'cross section' & 'cm2' are not = circumference.
The increased strength of the oval ice (loaded across its wider area) is pretty dramatic.
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verticon
Feb 19, 2010, 6:32 AM
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dadvntur wrote: I'm hung up on the "cross section" and "cm2" column definitions. Are they an area or the circumference? If it's circumference, then I can get the diameter of the three circular test ices you listed by the formula: radius = circumference/2(Pi); then multiplying the radius times 2 to get diameter. [That yields diameters in inches of 2.48" (line # 1), 6.2" (line # 2), and 39.1" (line #4).] But I'm guessing 'cross section' & 'cm2' are not = circumference. The increased strength of the oval ice (loaded across its wider area) is pretty dramatic.
"Cross section" is the area and "cm2" (cm^2 - square centimeters) is the measurement unit for it.
I managed to extract the table from the PDF file, check the attachment.
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Attachments:
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cascades_de_glace.jpg
(95.6 KB)
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minibiter
Feb 19, 2010, 6:55 AM
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decaNewtons is an odd unit to use. How old is this French study? Why don't they convert daN/cm**2 to Pa?
Must be those stinky Frogs trying to confuse the arrogant Americans.
COMMENT: 1daN = 10**1N. 10N. Not a whole hell of a lot of pro. I can spit harder than that.
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skinner
Feb 19, 2010, 7:34 AM
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I've slung columns before, but usually it's a couple of holes in a curtain of ice that are close enough together to sling. I look at it this way.. if I can reach in and and feed a a sling around a foot thick curtain, with no obvious cracks, chances are good that it's stronger then any v-thread I would make, tag a screamer on it and I trust it, despite that I have never tested it. I still climb with that idea that you don't fall on ice. The strength of v-threads is amazing, throw a screamer on it so as not to shock load it, and as long as the ice is sound, I really can't see why it wouldn't be at least as strong.. but the day I take a whipper on one (after I get all the sharp points removed from my body) I'll post my testimonial.
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verticon
Feb 19, 2010, 2:29 PM
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altelis wrote: What I'm talking about with regards to the linearity or to the scientist? If you don't get the scientists references....well you aren't a Dave Chappelle fan!
Aha, now it makes sense (I guess...) !
I might have seen that guy in a couple of movies, but indeed, I didn't watch any of his comedy shows.
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