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Bolt failure on North Wales limestone (Read 12515 times)

shark

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Bolt failure on North Wales limestone
May 29, 2013, 03:46:51 pm
https://www.thebmc.co.uk/bolt-failures-on-north-wales-limestone


A "Thunderbolt" climbing anchor in place on a route.

The failed bolt -showing the clean break on the bolt itself.

Following the failure of a bolt on a North Wales limestone route, the BMC is advising climbers to treat all ‘Thunderbolt’ anchors with caution. Read on for more details and advice on how to detect these bolts.

The bolt that failed was the first bolt on the route "One Ard 1-Der" a 6b sports route at the newly developed Craig Heulog on the West Shore of the Great Orme. The bolt that snapped was the first bolt in a four bolt route and snapped cleanly when the leader fell off while above the third bolt - therefore there was no direct fall onto the failed bolt, only the slight sideways tug of the quick draw as the rope went tight. This implies that the bolt failed at a low load.

Until a more thorough investigation is undertaken its not known what the cause of the failure might be. Until then, its advised that climbers treat all bolt placements with "Thunderbolt" placements with great caution. Enquiries and investigations are underway with first ascentionists and other route developers in North Wales to establish the extent of the problem. It's known that both this route and another adjacent route "Simpl-City" 6a both use these type of bolts, but these bolts will have been removed by BMC volunteers by this time.

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

It's possible that other recently developed routes at Castle Inn, Penmaenbach Quarry and other North Wales limestone venues may have been equipped with similar bolts. The routes known to have been equipped with these bolts were developed in late 2011 and its likely that only routes developed at that time or since that date are affected.

How to identify "Thunderbolt" bolts

"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.

The bolt head is embossed with the letters "APT" and "8 x100".
Conventional expansion bolts used on North Wales sports routes  tend to use 12mm "through bolts", where the nut that hold the hanger in place is separate from the bolt itself (see photos)
With the "Thunderbolts" the bolt head is flush with the hanger (see photos).

This issue will be discussed at the next BMC Cymru North Wales area meeting on Tuesday 4 June.
« Last Edit: May 29, 2013, 03:52:40 pm by shark »

Bonjoy

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What is more shocking, that a cheap none-stainless 8mm bolt failed, or that folk still use them in this context in the first place?

The rope access industry regularly uses (12mm versions of) these type anchors, as temporary and removable fixings. The article leaves some important questions unanswered. Was the bolt used as intended i.e as a self-tapper, or just glued into an oversized hole? Had the bolt been 'used' before? Self-tappers can be used repeatedly but the manufacturers advise against it as it could weaken the metal. What was the quality of the metal? This is of important in determining whether the brand was at fault or the whole concept of this type of fixing.


Doylo

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Pretty idiotic behaviour

danm

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There are a whole number of reasons why these were not an appropriate bolt to use; the focus at the moment is to warn climbers and to get a full tally of where they have been placed and get them removed. It's a real shame because there has been a ton of fantastic, high quality re-equiping going on in N.Wales over the last few years.

petejh

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The guy who placed those is an irresponsible idiot. The bolts he chose to use are unsuitable in five ways, in fact he failed about as badly as you can fail to choose proper equipment:
1. Non-stainless bolt in a marine area.
2. Stainless hanger on a non-stainless bolt - even if it had been a strong non-stainless through-bolt it would still have been badly corroded in only a few years.
2. A self-tapping bolt unfit for use as climbing anchors.
4. 8mm diameter, when the minimum recommended is 10mm (with 12mm through-bolts becoming more the norm).
5. He put a 12mm hanger on an 8mm bolt. Obviously all sorts of potential for unusual increased loading there.

Have we been time-warped back to the fucking 80s!??

The 8mm bolts were resin'd into a 10mm hole. Using resin suggests to me that the equipper suspected that these weren't fit for their intended purpose (holding repeated dynamic loading) when used in their normal way as self-tappers, and by using resin he's also just negated most of the cost-saving of buying those sub-standard bolts in the first place. The guy is clearly an idiot.

All the information for good bolting practice is easily-available for anyone who wants to find it - not just in the BMC's bolting advice sheets -  it's common practice all over the climbing world to use stainless 10 or 12mm through-bolts, from a reputable manufacturer, with known pull-out and shear strengths, on stainless hangers meeting EN959. He's either willfully chosen to not bother to find out good bolting practice - or worse, he's chosen to ignore it. In the process he seriously endangered other people through his negligence.

As we all know it isn't the BMC's place to provide new-routers with free equipment and hold their hands.

Nowadays most bad bolts - on Slate or NW Lime - have been re-equipped with one of four options - 10mm or 12mm stainless through-bolts and hangers, 12mm stainless resin or 16mm stainless resin. There are literally only three or four of crags left to sort out on NW Lime. Thankfully there aren't too many people around like the person who placed these bolts.

This doesn't alter my views on trusting bolts expressed in the last 'bad bolting practice' thread, Shark.

Oldmanmatt

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What worries me, as well as the points already mentioned; is where the bolt has broken.
I've been a Marine surveyor and accident investigator for about 15 years now and I've seen a broken bolt or two...
The bolt has sheared too far into the hole. Too far for a shearing force to have applied, surely? And the tension load on the bolt should have been well below material limits.
There appears to be resin past the point of failure.
It should not have been a point of particular load, such as the rim of the hole or where the hanger was in contact.
Most of the tension load (which would have applied to this fixing), would have come during installation (screwing in) of the Thunderbolt. HOWEVER, THIS BOLT WAS NOT USED OR FITTED IN THAT WAY (not actually driven in on the thread). There should have been no tension in the bolt.

So...

I would hypothesise that the bolt had been used previously and over loaded.

Or,

(And I bloody well hope not, since we fitted 120, 12x200, Thunderbolts in the last week)

It was a flawed bolt from the get go.


Closer examination of the patterns formed on the surface of the break, would give me a fairly clear idea of what precipitated the failure. Anyone got a high res photo of the break?



Oldmanmatt

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Oh, and whilst I can't think of a viable alternative, Stainless is a bummer in a marine environment (technical term). It is not immune to corrosion, and worse tends to corrode more in anaerobic environments, such as the root of a crack, leading to a fixing which looks great; but is in fact about to fail.
Corroded mild steel, at least is less likely to crack (more malleable, less brittle) and clearly shows its  level of corrosion.

Stainless staples must be the best for marine env. (Two bolts, in effect)?

petejh

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These duplex stainless bolts: http://www.bolt-products.com/SeaWaterSeries_000.htm are the best for marine environments. They're what we equipped LPT with, but they cost an arm plus additional leg.

SA Chris

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Surely someone must know who put them in? If they do he needs to say where else he has put them in before someone dies.

petejh

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We know who it was and his other routes are being checked out.

Luke Owens

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Well this sucks...

Glad no one got hurt!

Oldmanmatt

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These duplex stainless bolts: http://www.bolt-products.com/SeaWaterSeries_000.htm are the best for marine environments. They're what we equipped LPT with, but they cost an arm plus additional leg.

Ah yeah, that'd do it.

Saw them at Portland, but wasn't sure what was in the rock and had mistakenly taken them to be home made.

Not being an equiper, what's the resin life?

petejh

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From Bolt Product's website (Jim Titt):
'The general concensus seems to be that glued-in bolts have an almost indefinate life span. The D.A.V. tested some older bolts (up to 15yrs) and found no loss in strength.
The glues themselves when cured are chemically inert and should not degrade though some weakening from water has been observed with polyester. Additionally they often contain cement powder as a filler which provides an additional long term fixing. The glues used in the construction industry have an expected life span of at least 20yrs and the European standard for chemical anchors gives a life of 50 years as a reference point for designers.'

There are staple bolts on the Ormes placed in the 80s using polyester resin. There are also dmm eco bolts placed in the early 90s. There aren't any known instances of either of these types failing under load, but they haven't been pull-tested so who knows how strong they are.

petejh

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Also:

'Long term load tests.
There has been extensive research in the construction industry on the effects of long term continuous loading ( Meszaros/Lehr for example) but rock anchors for climbers are not usually under this type of load. However the fact that the tested anchors have withstood 50% of their breaking loads for test periods of years gives one confidence in their life span. Polyester displays some creep especially when damp and under freeze/thaw conditions and a better choice would be vinylester or epoxyacrylate if these are to be expected.
Repeated high loads are a concern for many who consider that repeated leader falls will weaken the bolt. We know of no other manufacturer who has published cyclic load tests on anchors for climbers but we have put a bolt through 1000 rapid cycles of 0-25kN axial loading, then increased the peak by 5kN at a time for 100 cycles each until ultimately the block failed at 44,6kN.'
From:  http://www.bolt-products.com/Glue-inBoltDesign.htm

Oldmanmatt

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2.5 tonnes and 4.4 tonnes respectively...


Should be ok...

petejh

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Some of this person's other routes have now been checked out. On the route next to the one on which the bolt snapped, another thunderbolt snapped whilst being unscrewed. The bolt was unscrewed using a small socket handle with a torque setting, it snapped at 25Nm - that's light hand pressure. There's no doubt it would have failed had someone fallen on it.
Another route on the same wall equipped by the same person had cheap zinc-plated through bolts and stainless hangers. The first bolts on this route have been removed. The rest will be removed later and the hangers returned.
Another route in Penmaenbach Quarry, same person, was equipped with cheap zinc-plated through bolts and stainless hangers. Those hangers will be getting returned and the bolts knocked flush.

There might be some routes at Castle Inn quarry similarly badly-equipped, I don't think anyone's checked yet.

SA Chris

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Returned accompanied by some strong words no doubt! Created a load of work for other people - maybe he should be told to go and make good?

cheque

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This is proper scary!

Respect to the people involved in sorting it out.  :bow:

I'll be donating to the North Wales bolt fund by way of thanks.

Luke Owens

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Wow, snapped under light hand pressure...

It really makes me feel rather sick to think that I climbed on that wall when It was first developed and I hadn't been climbing long.

I just hope the equipper understands the extent of their incompetence...

Thanks to whoever is getting rid of the bolts.

petejh

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Some sort of araldite type glue had been used, which wasn't set.


Thanks due to Andy Boorman and Danny Garnett for doing the work.

kc

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So when it was reported that resin was used, do you think that was just a bit of araldite on the head or were the holes injected with resin?
I say this because it would presumably be quite difficult to extract these bolts if they had been properly glued in without the heads shearing off.
There seems to be no residue on the shaft. Meaning they may well have been cranked in cutting their own thread.
I have used 10mm thunderbolts before to clean and prepare projects and it takes quite a considerable amount of force to get the thread to bite. With anything less than 10mm it  would be so easy to sheared heads off and most definitely start to twist the metal.

Bonjoy

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Aye, it's all still a bit vague. Not enough info to judge why they failed. I'd guess, as others have, that the metal had been weakened by the screwing in process. As to whether that was during the final installation, or a prior use, who know? The hardness of the rock, if it is much more so than concrete, might put extra load on the fixing during installation. Ironically the fixings in the second shot look excessively long, the sort of thing you’d want to use in soft masonry or mortar, which would mean they took a lot of turns to get in. When it comes to bolts (with some caveats) the extra length doesn’t increase fixity past a certain multiple of the diameter.

kc

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kelvin

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Trad is looking appealing again. I must admit to not having done much sports climbing and as such, have not really given bolt funds much thought - seeing this, I'll make sure I contribute in future and badger my mates to.

hongkongstuey

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These duplex stainless bolts: http://www.bolt-products.com/SeaWaterSeries_000.htm are the best for marine environments. They're what we equipped LPT with, but they cost an arm plus additional leg.

that's what we've started using in HK too - have a hundred of them in sat in the closet waiting for suitable projects to be identified (they might be waiting a while though as its currently 34 deg and 90% humidity)