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Top rope fall analysis w/ strain gauge analyzer:
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USnavy
Mar 14, 2012, 8:16 AM
Views: 16647
Registered: Nov 6, 2007
Posts: 2667
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I recently purchased a 500Hz. strain gauge analyzer and 5000 lbs load cell that I can use in the field with my laptop, so I decided to do some testing on TR falls today. This is just some quick non-scientific testing to familiarize myself with the equipment, so don’t take anything in here too seriously. I took six falls of varying length and catch method (i.e. hard catch, soft catch, ect.). The graphs below represent the most serious of the six falls. Basically I wanted to determine what would be the highest impact force I could produce on the anchor while top roping without doing something extremely dumb, like taking a huge TR whipper on static rope.
Here are the specs:
-160 lb climber
-175 lb belayer
-Mechanically locking belay device
-9.9mm Maxim Glider, 9.5 kN impact force rating, 29% dynamic elongation, 5% static elongation
-Hard catch (the belayer just stood there and locked off)
-50 feet of rope out, 12 foot free fall, 20 foot total fall distance (approximate, not measured)
To start with, some really crappy pictures of the set up:
Next, the fall graphed out:
This next graph represents the loading that was in the upper 50% of the fall range. The peak load was just shy of 700 lbs. so this graph shows the loading above 350 lbs. The numbers on the X axis represent the duration in milliseconds multiplied by ten.
This last graph captures what I am going to call the “high” or “mean peak” meaning it shows how long the force stayed in the upper 10% range of the fall range, or above 600 lbs. This graph would be useful to compare different falls of the same fall factor, but different fall lengths, because it shows how long the anchor experiences the peak force of the fall. As you can see the loading on the anchor was only in the top 10% for 160mS.
So the maximum impact force on the anchor with a 12 foot free fall on TR was 3.09 kN. Keep in mind, I pulled out a fair amount of slack before I let go and my belayer gave me an intentionally hard catch. So your average TR fall will likely produce less of an impact force on the anchor, unless you weight a lot more than me.
(This post was edited by USnavy on Mar 14, 2012, 10:21 AM)
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Edit Log:
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Post edited by USnavy
() on Mar 14, 2012, 10:21 AM
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