Forums: Climbing Information: The Lab: Re: [adatesman] Holding power of ice screws: Edit Log


Jan 24, 2009, 8:40 AM

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Re: [adatesman] Holding power of ice screws
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How come that all my recent serious threads get moved? Nevermind, here is the second part on the holding power in glacier ice.

Again, it is in german, so here is my translations of the main points:

This time they did not place the screws in different ice qualities, since glacier ice is more or less of constant quality. They did however remove snow and rotten ice from the surface, to get to the good ice below.

In this test they used not just medium length screws, but different lengths.
What they found is the following:
13cm screws had an average holding power of 18,6 kN
16 cm screws had an average holding power of 19,6 kN (for comparison: average in good waterfall ice 19,8 kN)
22 cm screws had an average holding power of 20,7 kN.
They produced some nice graphs with the deviations, wich i have translated for you:

Furthermore they tested the holding powers versus the angles of placement with some 13cm screws, where the neutral one (0) had the best holding power, followed by the hanging one (-15). The one placed with the hanger pointing up had a significantly lower holding power.

Another thing they mention is how the screws fail. In the cold and brittle waterfall ice in the previous test they observed how the screws broke with the ice in a large area. In the softer and warmer glacier ice the screw simply got pulled out of the hole, leaving the hole almost intact. However when they did the test on glacier ice in cold conditions they observed a similar failure mode as in waterfall ice.

They conclude that glacier ice and good waterfall ice offer similar holding powers, so all tested screws can be considered safe.
They say that not the length of the screw is important for the holding power, but the number of threads on the tube.
Another thing they mention is the problem of "pressure melt out", when you weight the screw constantly, for example in a belay or toprope situation. This is a bigger problem in warmer ice, and with shorter screws, so you need a backup behind your main screw.

And last but not least they almost killed a biner toproping in a shockinly short time, since the rope did take up a lot of glacier debris and acted as a saw on the biner.

And there is even more stuff in this articles on ice threads, which i will bring to you soon.


(This post was edited by qwert on Jan 24, 2009, 8:42 AM)
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Post edited by qwert () on Jan 24, 2009, 8:41 AM
Post edited by qwert () on Jan 24, 2009, 8:42 AM

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