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Chockstone Forum - Gear Lust / Lost & Found

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 Page 1 of 2. Messages 1 to 20 | 21 to 23
Author
In Situ Carrot Testing

tnd
6/12/2010
10:48:31 PM
Fellow Chockstoner George and I took the test rig to the suburban Sydney crag of Berowra on Sunday to extract some carrots which had been in place for 25 years. These were on the mighty line of Daily Grind (25), one of Mikl's testpieces, having been left there after it was rebolted. Described by PMonks on Sun, Surf and Sandstone as "2 manky BRs close together", we thought these would be an ideal subject for testing and laughably easy to remove. How wrong we were...

After a morning warm-up sweating in 95% humidity on some of the routes on Bullet Hole wall, including skating up a soaking wet Mental Fatigue Direct Start, the sun came out and we felt ready to set up the equipment. 45 minutes of (f)rigging later and we were in place with the unit dangling between us, on the clean grey just-under-vertical wall.


The rig in place with George poised ready to record results


Carrot 1 - some of Mikl's finest work from the mid-80's

First candidate was a well placed clean looking carrot, probably originally galvanised but now slightly rust coloured. We connected the cylinder to the carrot using a bracket Mikl had made from high strength 3mm stainless sheet, which had worked well when trying it on a glued in carrot in his back yard. I pumped and pumped and at 2,000 pounds per square inch (psi) of hydraulic pressure (equivalent to about 8kN pullout force) the bracket distorted and slipped off the carrot head.

We ditched the bracket and fitted two bolt plates. At 4,600psi (~21kN) these had stretched so much they were about to flip off the head so we called a halt.


Brackets stretching - they'd got a lot worse than this just before we stopped

We moved on to the next bolt, a classic droopy number of the kind which is often clipped in trepidation by a trembling leader. Surely this would offer little resistance?


Carrot 2, sadly pointing southwards

With plenty of room on the bolt shaft we were able to fit four bolt plates to beef up the system. I grunted and pumped and grunted and pumped and was about to give up when there was a loud crack and something exploded outwards and hit the ground. The bolt had pulled along with a shallow cone of rock - at 5,600psi (~26kN)!


40mm embedment holding 26kN


Bolt hole showing the cone-scar

I don't know what the young Mikl was pounding these bolts in with back than or what porridge he was eating for breakfast, but whatever he was doing it worked.

What conclusions can we draw from this? Well, with a sample size of two, none that could be extrapolated to any other carrots you can find. There are plenty more around the place so with some improvement to the rigging system and a better tool to fit on the bolt head we may do this again.

The trouble with carrots is that the odd bad one - maybe numbering less than 1 in 20 - will pull out really easily, but looks just like all the rest.


Modified bolt plates anyone?
One Day Hero
7/12/2010
12:01:07 AM
Cool, carrot bolts strengthen as they rust, I love it!
mikllaw
7/12/2010
8:43:24 AM
I always thought most of my bolts were solid, but I've had a few come out attached to unfortunate leaders:-
Ordeal by fur (but that was when it was still graded 21) diamond bay sydney, bolt #2, could have been nasty
Psychodrama 22 Mt Piddington, top bolt, 6m above the last, fell out as crunch moved past it I think
Purple denotes bruising 23 araps, I never found out whether the name was true in this case (did it fail or was it pulled cos' it looked terrible)
half the bolts at narrabeen steep side came out by hand with a quickdraw



tnd
7/12/2010
9:13:35 AM
On 7/12/2010 One Day Hero wrote:
>Cool, carrot bolts strengthen as they rust, I love it!

26kN exceeds the European standards. Perhaps we should submit them for approval...

nmonteith
7/12/2010
9:16:32 AM
Maybe its not such a good idea to do anymore testing on real routes on real crags. That cone failure is one big ugly scar!

tnd
7/12/2010
9:37:12 AM
It's not as noticeable from the foot of the cliff as it looks on that close-up Neil. And it is Berowra - there are more routes squeezed in than you could poke a stick at, and old cars dumped below!
egosan
7/12/2010
10:43:37 AM
Could old carrots be tested like old pitons? The "do they still ring" test? or some other tactile test?

skink
7/12/2010
11:01:03 AM
On 7/12/2010 egosan wrote:
>Could old carrots be tested like old pitons? The "do they still ring"
>test? or some other tactile test?

Jim Titt's website has some interesting info on pitons, see http://www.bolt-products.com/Glue-inBoltDesign.htm, Part 6 way down the page.

See particularly Myth 3 regarding the "ring test" for pitons.

And I think the observation near the end regarding piton reliability is equally valid for carrots - "A piton can only be trusted on the day it was placed and only the climber who placed it can give an opinion on its reliability, anything else is only a guess"
mikllaw
7/12/2010
12:02:24 PM
On 7/12/2010 egosan wrote:
>Could old carrots be tested like old pitons? The "do they still ring"
>test? or some other tactile test?

You could modify this test---When chopping bolts I start by putting a spanner on them and trying to twist them out. If you assume the bond's resistance to twisting is the same as the resistance to pullout, then multiply the twist force by the ratio of the spanner length/bolt radius.

For a 150mm spanner and 10mm bolt (r=5) the ratio is 30. The if you twisted to 10 kg force (a lot!) before the bolt spun in the hole, it would have come out at 300 kg ~ 3 kN.

About 10% of bolts twist loose, the rest are stuck in and need to be neatly chopped - hit them flush with the roock from 4 directions with a cold chisel, then twist thema nd they will snap off flush with the rock.
mikllaw
7/12/2010
12:45:55 PM
On 6/12/2010 tnd wrote:
>
>The rig in place with George poised ready to record results

George, you look like the construction dude from the Village people

Look at all the clobber, it's much harder pulling them out than putting them in.
mikllaw
8/12/2010
8:30:59 AM
And most famous carrot removal incident was what the rig, Robbie" was named after, when Rob LeBreton pulled an abseil bolt, fell 30m and was choppered out.
mikllaw
9/12/2010
12:06:02 PM
Last week I pounded in 8 carrots (3/8 inch x 75 mm) into pretty good rock with a range of grinds and hole sizes and pulled them straight out this morning. They were all sticking out about 10mm and looked 'ok'. Failure loads next to each one.

variability eh! Anything under 2 kN is extra worrying, as people treat these like, um, bolts, you know

nmonteith
9/12/2010
12:14:19 PM
Were the ones with the low pull out strength only lightly tapped in? Those results on the most part are appalling. Does that mean that rust is what is holding in the older bolts which held 20kN??
mikllaw
9/12/2010
12:57:48 PM
On 9/12/2010 nmonteith wrote:
>Were the ones with the low pull out strength only lightly tapped in?

yes, but I couldn't remember which ones by the time I came to test them, just like clipping them really.

>Those results on the most part are appalling. Does that mean that rust is what
>is holding in the older bolts which held 20kN??

Yup, peeing in the hole might be the best way to get them to hold

voodoo
9/12/2010
2:04:10 PM
For those of us failing Dr Law's patented eye-test...


Butters81
9/12/2010
2:43:53 PM
On 9/12/2010 nmonteith wrote:
>Those results on the most part are appalling. Does that mean that rust is what
>is holding in the older bolts which held 20kN??

With a sample size of 2, I don't think you can make any conclusions about the pull out strength of older carrots

ambyeok
9/12/2010
2:53:00 PM
On 9/12/2010 Butters81 wrote:
>With a sample size of 2, I don't think you can make any conclusions about
>the pull out strength of older carrots

Hater.

Butters81
9/12/2010
3:02:19 PM
Just repeating what Niall said in the original post

tnd
9/12/2010
3:34:33 PM
On 9/12/2010 davidn wrote:
>
>Can a chemist or someone smarter than me explain how rust would bond with
>rock and whether it would vary for different types of rock? Because surely
>friction can't account for that much of an increase.

Mr Law the materials engineer might be able to shine more technical light on this, but as far as I know, when the iron in steel becomes iron oxide (rust) it takes up more room and so will tend to tighten the bolt in the hole. Some of the rust may even grow into the rock. Mikl?
mikllaw
9/12/2010
3:36:59 PM
Rust (iron oxide) is about 4 times the volume of the original iron. It also infiltrates the sandstone, so there is more of an interference fit than you can get by simply pounding harder, and there is an increased bond too. And then it rusts too much and then head falls off.

 Page 1 of 2. Messages 1 to 20 | 21 to 23
There are 23 messages in this topic.

 

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