Bolting Clinic at RRGCC's "Rap n Rawkus"

Post by **weber** » Mon May 30, 2005 8:15 pm

Just a quickie summary of the bolt testing portion of last Saturday's Bolting Clinic at Muir.

About 15 people showed up to see a demonstation of destructive bolt testing. We were originally only going to demo one test of a bolted hanger. But, the interest was high after blowing out the first one that we ended up doing three more - a total of four different bolts. I left my detailed notes at the barn, but here's what I can pull off the top of my head. During the testing, I reported only the ball park values to the "spectators." These figures were based on the calibration factors for this test setup and are, therefore, more accurate:

1/2-inch "hardware store grade" sleeve stud with nut. Metolius hanger bracket. Subjective grading of the rock drilled - soft to moderate in hardness. Depth was approximately 3.5 inches. Stud failed in shear at 3360 pounds.

1/2-inch ITW Powers "red" sleeve bolt. Metolius hanger bracket. Subjective grading of the rock drilled - soft to moderate in hardness. Depth was approximately 3.75 inches. Bolt failed in shear at 4200 pounds.

12mm Petzl "Long Life" nail drive bolt. . Petzl hanger bracket. Subjective grading of the rock drilled - soft to moderate in hardness. Depth was approximately 2.5 inches. Rock failed in tension at 4700 pounds. The bolt itself did not fail. This was a big surprise. None of us present expected the bolt to survive half this force. These are great anchor bolts for hard rock, but are not designed nor recommended for use in soft sandstone such as that found in the Red.

1/2 ITW Rawl type Powerbolt sleeve anchor bolt (blue). Metolius hanger bracket. Subjective grading of the rock drilled - soft to moderate in hardness. Depth was approximately 3.75 inches. Hanger bracket failed in tension at 7640 pounds. The bolt was bent but did not fail. The Metolius hanger bracket performed well above its UIAA-rated strength.

PLEASE note. This is PRELIMINARY info.When I get my notes and re-check the calibration of the cylinder. The info could change. I am not even certain that the nail drive is a Petzl brand. Tim Powers had just borrowed it from Mark Meyer, and I need to verify its manufacture. (We owe Mark for one nail drive.)

Rick

Post by **t bone** » Tue May 31, 2005 3:33 am

Thanks Rick, we really had fun. The nail drive was a Petzl longlife bolt. Just seeing that hanger getting ripped was amazing.

Post by **Danny** » Tue May 31, 2005 3:59 am

That is really cool that you guys are doing these tests. Can you provide more detail on how the test was done? Are you pulling straight out, at 90 degrees, or somewhere in between?

Post by **weber** » Tue May 31, 2005 11:37 am

Danny wrote:That is really cool that you guys are doing these tests. Can you provide more detail on how the test was done? Are you pulling straight out, at 90 degrees, or somewhere in between?

We've done some tests with the puller suspended from a tripod so that it pulls the bolts straight out:

And, the more recent tests were pulling down substantially at a right angle to the bolt axis, i.e. in the direction that a climber's fall would stress the bolt. The recently posted photo shows the puller mounted to a vertical wall attached via a 3/8" chain to a bolted hanger above.

Rick

Post by **ynp1** » Tue May 31, 2005 7:16 pm

how much force does the average or even above average fall generate?

Post by **weber** » Tue May 31, 2005 8:55 pm

ynp1 wrote:how much force does the average or even above average fall generate?

This is a frequently asked question. I wish there were a meaningful answer other than "it depends." But that's the bottom line. Unfortunately, defining "average fall" is impossible.

Here is the practical answer IMO. A typical climber/belayer system has several places where "give" occurs. Without this give, a high impact force could be easily generated. And, in such a non-forgiving situation, a climber's backbone would be snapped long before a properly installed hanger would fail. In other words, if your body creates enough force to rip out a good anchor bolt, you will probably will die from the rope jolt rather than the final impact with the ground.

Your question is good. And, one really meaningful way to determine this "average" force is to put a load cell (a force measuring transducer) on your harness and attach the rope to it. Then, take your "average fall" and we'll record the force generated. I have load cells and data acquisition instrumentation that can sample at about 240 times per second. This could provide a nice time plot of the varying force throughout the fall. Want to try it sometime? Perhaps others would want to try it with their "average" falls. Sounds like fun, too.

Rick

Post by **dhoyne** » Tue May 31, 2005 9:12 pm

I'm willing to take a whipper on a load cell. That way all of you can safely know that you're generating less force than I can.

Is this something that could be rigged up at CTT Rick?

There's so many factors though -- rope, harness, belay device, type & # of biners the rope is going thru, slack, give or slippage by the belayer, clean fall vs. scraping off the rock, and of course distance (and probably others!). I don't think you can ever have an 'average' fall.

Post by **neuroshock** » Tue May 31, 2005 9:38 pm

dhoyne wrote:I'm willing to take a whipper on a load cell. That way all of you can safely know that you're generating less force than I can. Is this something that could be rigged up at CTT Rick?

There's so many factors though -- rope, harness, belay device, type & # of biners the rope is going thru, slack, give or slippage by the belayer, clean fall vs. scraping off the rock, and of course distance (and probably others!). I don't think you can ever have an 'average' fall.

couldn't you simulate a worst-case scenario, thusly knowing that anything encountered in the real world ('average' fall) is generating less force?

like 160-200lbs of weight attached to a load cell attached to a static line clipped through the first 2 bolts (say, 1st at 12' and 2nd at 19') dropped from the 3rd bolt (26') onto a gri-gri/clove hitch/fig-8 anchored to the ground?

no dynamic rope, no rope slippage, higher fall factor, and no body in the harness to break.

Post by **weber** » Tue May 31, 2005 10:30 pm

neuroshock wrote:
dhoyne wrote:I'm willing to take a whipper on a load cell. That way all of you can safely know that you're generating less force than I can. Is this something that could be rigged up at CTT Rick?

There's so many factors though -- rope, harness, belay device, type & # of biners the rope is going thru, slack, give or slippage by the belayer, clean fall vs. scraping off the rock, and of course distance (and probably others!). I don't think you can ever have an 'average' fall.
couldn't you simulate a worst-case scenario, thusly knowing that anything encountered in the real world ('average' fall) is generating less force?

like 160-200lbs of weight attached to a load cell attached to a static line clipped through the first 2 bolts (say, 1st at 12' and 2nd at 19') dropped from the 3rd bolt (26') onto a gri-gri/clove hitch/fig-8 anchored to the ground?

no dynamic rope, no rope slippage, higher fall factor, and no body in the harness to break.

My opinion is that your scenario goes beyond a worse case inasmuch as it would kill or severly injure the climber. But, I agree that a worse case scenario wherein a human could survive could be created. Because no responsible climber would lead on a static rope, the test scenario should be done on a dynamic line. IMO

Dave - Sorry, what is CTT?

Rick

Post by **J-Rock** » Wed Jun 01, 2005 12:38 am

Climb Time Towers. I like to skip the last clip and let go at the anchors to take Karla for a nice ride up the wall. 8)