Forums: Climbing Information: The Lab: Holding power of ice screws: Edit Log




qwert


Jan 24, 2009, 4:00 AM

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Registered: Mar 24, 2004
Posts: 2394

Holding power of ice screws
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Good news everybody!
Ice screws are much more secure than one might guess!

So i came upon this article by the german alpine club DAV, where they tested the holding powers of ice screws.
As you can see, the article is in german. So the friendly guy that i am, i am trying to give you the main points in english:

for this test they divide the ice the screws where placed in (in an actual frozen waterfall) into three categories:
Good: compact ice with a solid base
Medium: ice with 10 to 20% voids (either air or snow filled)
Bad: Dont know how to translate. that ice that is kinda made up of small tubes, with 30 to 50% void space.

So at first they did a rather small test in 2004, where they placed a 16cm screw in good waterfall ice, and found out that their puller cant do more than 22,8kN, whereas the screw and the ice could still take more. With further tries they managed to kill a biner and a bolt, but no screw.
Then they switched to shorter screws, where they finally had "success" with a 10cm screw, wich they placed in good, but only 15cm thick ice. At 10kN the ice failed, by breaking out large and cone shaped.
At medium quality ice they found an average holding power of 15kN for 16cm screws, and values of 11 and 18 kN for 12 and 13 cm screws (they dont tell how many they used, but i assume it was only two of the short ones).
At bad ice they give the two values of 1.2 and 13 kN ('but not how many, or how long screws).

So after this, they did a new and bigger test in 2005, to get a better database, this time only with medium length screws (BD 16cm, grivel 17cm and charlet 18cm) and some snargs. They say they destroyed 49 screws and 5 snargs.
They placed most of the screws 90 to the ice surface. In good ice they managed to break two hangers (at 13,2 and 15,6 kN) and one tube (at 18kN), but apart from this they just had the ice get some cracks and produce some sounds, before they had to stop at around 19kN because of their puller.
In medium quality ice they had an average holding power of 9,6 kN, however with some values like 4,3 and 18,3 kN.
They give some percentages about the ability to hold a fall for the screws, where they use 10kN as safe and 5 to 10kN as marginal, and everything under 5 as likely to fail.
So 56% of the screws in medium ice would have been safe, 13% marginal and 31% fail.
In bad ice they found the average holding power to be 5,6 kN with values from 1,2 to 13kN. Or in percentages: 13% would have been safe, 13% marginal and 56% would have failed. So there must be a typo somewhere.
I took the freedom to translate the diagram for it:

I guess its pretty self explanatory. The colored dots mean:
red:test stopped
yellow: screw failed
blue: ice failed

As mentioned they also tested snargs. They all failed under 10 kN, so they are not recomeded for use. (One placed at a hanging angle didnt even hold body wheight)

Also they had a look into the angle of the screw, where they found that srews placed in a hanging orientation (up to 30) generally hold more then screws pointing up.

Their conclusions are that medium length screws are fine for all purpose use, and the reccomendation to only use the longest screws for belays is not neccessary. Accoring to this article a 2 screw belay in solid ice can be treated like a 2 bolt belay.
Furhermore they conclude that even the shortest screws can hold hold a fall in good ice. Bad ice should be considered as what it is and if you dont have anything else, try to cluster together a few screws.

Hope that interesting for you.
They also did some tests in glacier ice, which i hopefully will provide you soon. But given that i am sick, my foot is still kinda busted and my boots are in italy for repair anyways, i should find the time for it rather soon.

qwert


(This post was edited by qwert on Jan 24, 2009, 4:01 AM)
Attachments: Eischrauben1.jpg (17.2 KB)



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Post edited by qwert () on Jan 24, 2009, 4:01 AM


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