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Chockstone Forum - General Discussion

General Climbing Discussion

Author
Bolt failure in the UK
barney800
30/05/2013
5:08:24 PM
I thought people on here might be interested to know that a "Thunderbolt" bolt on North Wales limestone has recently failed under a very low load:

https://www.thebmc.co.uk/bolt-failures-on-north-wales-limestone

Is this type of bolt in widespread use in Australia?
argos44
30/05/2013
8:23:35 PM
Sounds like a Screwbolt.
Screw Bolts

"Gold Coloured Head" = Cadmium Plated (Non Stainless)

Either snapped from corrosion or maybe stresses from over tightening them in hard rock?


nmonteith
30/05/2013
10:57:07 PM
I have only seen these bolts used as temporary 'doggers' to help aid into steep routes in Australia. Being cad plated makes them unsuitable for long term anchors.

rodw
31/05/2013
7:24:56 AM
Yeah we been using them as temp bolts to re direct a rope or a set of them for anchors when no trees up top for bolting...bomber when they go in, but doubt they would stay that way

pmonks
31/05/2013
7:57:42 AM
Wait - there are bolts in the UK? Do the pommies know?!?
mikllaw
31/05/2013
8:17:38 AM
"Thunderbolt" bolts are self-tapping threaded bolts with a fixed hexagonal gold coloured head. The one that snapped was an M8 x 100mm that had been placed in a drilled hole and resined in place with a Petzl hanger placed on the bolt. The hanger did not fail - the failure appears to be a clean break of the bolt itself, some 14mm in from the hexagonal bolt-head, inside the drilled hole."

8mm threaded? yuck.

I would have thought that glued in would be less likely to snap than the usual method of screwing it inas hard as possible. otherwise, this is exactly the same failure mode as was seen 15 years ago on taipan wall.

Amusingly one of the first hits on Google is for grampians fasteners...
http://www.grampianfasteners.com/thunderbolt.aspx

The good Dr
31/05/2013
10:03:02 AM
Similar to the type of ring bolt that HB installed that failed. The "Thunderbolt" may have been over torqued (8mm shaft). The other related issue, though possibly not the cause of this failure, is Zinc plated bolts with a stainless steel hanger. Corrosion will occur at an accelerated rate at the interface of the stainless steel and Zinc/mild steel. It is the zinc/mild steel that will corrode and this will remain hidden.

Robbie
31/05/2013
11:09:18 AM
Lets talk the Torque!

As you know fasteners (nuts and bolts) come in a variety of sizes, but who of you know that they also have different strength ratings. I'm pretty sure we all know the outcome of under tightening a fastener. However, what can over tightening lead to. Check out the Wiki link for some info on Torque Wrenches. A great tool for getting it right when it come to specifics Simply put, if HB and our Prime Minister were to be tasked with placing a masonary fastener the fastening results would be the same using a Torquer Wrench.

http://en.wikipedia.org/wiki/Torque_wrench
mikllaw
31/05/2013
12:00:36 PM
If it was glued in, it probably wasn't torqued. Though you never know what happens when nufnuf place bolts.
There are also a bunch of these on "An inconvenient truth" at narrowneck placed by someone who thinks that stainless steel is a hippy myth.

The good Dr
31/05/2013
1:11:13 PM
May have been 2nd hand off a construction site!
Dave C
1/06/2013
12:09:28 AM
More info on here; http://ukbouldering.com/board/index.php/topic,22388.msg409266/topicseen.html#new

It's the mild steel / stainless combo that makes me cringe, particularly in a marine environment!

Robbie
1/06/2013
1:16:50 PM
Oils aint Oils

Fastener Application Scenarios
1. Bolts that attach a D-ring tow bracket to the bumper face (Think Hummer and Big Chrome Bumper Shackles) of a motor vehicle would be critical under tension. So you would want to know that the tensile strength of the particular set of bolts is suitable. For example, think a snatch strap being tensioned under super dynamic loading, and you are the tow vehicle. The possible chain of events: (1) Tension, (2) Bolt failure, (3) missile launch, (4) terminal velocity, (5) impact. “Got the picture.”
2. Bolts that attach winch-mounting plates are typically seeing mostly shear loads thus preventing the winch from departing from the motor vehicle during winching operations. In that case, shear strength is important.

Fastener Grades. There are different types of strengths listed for each grade.
• Proof strength (about 90% of yield), ultimate tensile strength (bolt fails in stretch)
• Yield strength (bolt begins to get a permanent set and changes crossectional area typically)
• Shear strength (bolt prevents parts from separating by using its shank or body as a stop).

So, depending on how you are using a fastener, you would look at the appropriate and corresponding strength type needed. Wouldn’t you?

Ponder this one as you approach you next clip on a climb at your favorite crag. As you know the strength rating of the crabs on the quickdraw you are about to use? If you don’t have a look at the spine of one of the carrabiners, now have a look at the head of the bolt\nut of the fastener you are about to clip, the one with the hexagonal thingy! If you can just reach for the check list in the chalk bag. (And breathe) “Now, which grade of bolt is that?” “Watch me…………..”

Check out the following links for a broader technical view.

http://www.dot.state.il.us/materials/fasteneridentificationguide.pdf

http://www.tmr.qld.gov.au/~/media/busind/techstdpubs/Technical%20notes/TN62assemblytensioninghighstrengthboltsnuts.pdf

Safe climbing :-)
daviesdan
2/06/2013
1:23:02 PM
From the BMC webpage..

"The manufacturers of "Thunderbolt" have categorically stated to the BMC that this product is not tested or recommended for the purposes of fixing climbing anchors."

Guess they would say that though...

The good Dr
3/06/2013
7:16:52 AM
On 2/06/2013 daviesdan wrote:
>From the BMC webpage..
>
>"The manufacturers of "Thunderbolt" have categorically stated to the BMC
>that this product is not tested or recommended for the purposes of fixing
>climbing anchors."
>
>Guess they would say that though...

And the manufacturer is incorrect because?
barney800
5/06/2013
6:37:09 PM
This whole story has made me realise I don't know enough about assessing bolts as I ought to. If they're obviously corroded, deformed or sticking way out the rock I know to be wary. Other than this, what other things should I be looking out for?

nmonteith
5/06/2013
6:47:33 PM
On 5/06/2013 barney800 wrote:
>This whole story has made me realise I don't know enough about assessing
>bolts as I ought to. If they're obviously corroded, deformed or sticking
>way out the rock I know to be wary. Other than this, what other things
>should I be looking out for?

Anything with a gold tint should be a concern (signifies non-stainless steel) . Use common sense - if a bolt doesn't look like anything you have seen before then treat it with caution. If in doubt back it up or back off.

Macciza
5/06/2013
8:18:34 PM
>On 5/06/2013 barney800 wrote:
>>This whole story has made me realise I don't know enough about assessing
>>bolts as I ought to. If they're obviously corroded, deformed or sticking
>>way out the rock I know to be wary. Other than this, what other things
>>should I be looking out for?
>On 5/06/2013 nmonteith wrote:
>Anything with a gold tint should be a concern (signifies non-stainless
>steel) . Use common sense - if a bolt doesn't look like anything you have
>seen before then treat it with caution. If in doubt back it up or back
>off.

Also don't just accept and believe simplistic statements like this 'goldtint = concern' crap . . .
Yes it is most likely not stainless steel but that does not mean it is inherently bad by any means.

The bolt mentioned in the above report should have been fine- definitely over 20kN shear - and obviously was as the route had been climbed many times. Though obviously it has failed suddenly but why?
To me the most likely scenario is that some idiot do-gooder safety nazi got up there with a spanner because the hanger seemed a little loose and they tried to 'tighten' the bolt up not knowing it was glued in. This has produced a stress crack which resulted in the subsequent failure. There is really no reason why a standard functional bolt would simply snap 'for no reason'.

Anyway just do a bit of broad research on the strength of various bolt sizes and you will realise that often things are not as bad as some people make out.
mattbrooks
7/06/2013
4:03:55 PM
8mm in this type of bolt is no good. We minimmum 10mm just for dogging bolts and after the scenario on Taipan I would not recommend them as a permanent solution.

Macciza
7/06/2013
6:07:22 PM
On 7/06/2013 mattbrooks wrote:
>8mm in this type of bolt is no good. We minimmum 10mm just for dogging . . .

Really ? How about checking some stats? you ret
8mm this type of bolt = over 20kN tensile & shear strength!! Fine for dogging !!! 10 mm is overkill . . .

PS It also helps if you can actually tell the difference between rock that has been minimally scratched with a soft, clayey rock leaving no damage and rock that has been 'carved away' . . .

There are 19 messages in this topic.

 

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