Three bolts of just under a meter in length have failed in as many months on London’s second tallest building, causing the building’s owner to replace dozens of bolts and raising fears more will fail.

In its latest announcement, London based developer British Land has acknowledged that following the earlier collapse of two bolts on its 224 meter Leadenhall Building in November, a third bolt had recently fractured and was captured by precautionary tethering put in place late last year following the collapse of the other bolts.

The company said site and laboratory testing of both the broken bolts and several other bolts by contractor Laing O’Rouke and structural engineering outfit Arup had confirmed fears the problem was caused by a material failure mechanism known as hydrogen embrittlement – a crack growth mechanism within the bolt material whereby according to the Gizmodo web site single atoms of hydrogen enter the steel, migrate through the crystal lattices and attract themselves to the area of highest stress where they cause small fractures to propagate and, in worst cases scenario, a cascading effect as the stress increases and attracts more free hydrogen, leading to a sudden catastrophic failure such as the shearing of a bolt.

Such a phenomenon creates substantial headaches regarding safety as it can cause bolts which have previously shown no sight of stress to snap suddenly as opposed to deforming over time and showing signs of stress during inspections.

In a statement, British Lands said the tests had indicated the building’s overall stability was not in jeopardy.

“These confirm that the problem is limited to certain bolts,” the company said, adding that a program to replace the bolts would take place as a ‘precautionary measure’.

“Arup has also confirmed that there is no adverse effect on the structural integrity of the building.”

Designed by Rogers Stirk Harbour + Partners and completed in September, the Leadenhall building – which is known as the Cheesgrater – is renowned for its sloping profile which was created to preserve the views of St Paul’s cathedral, and at 47 storeys in height is listed by the Council on Tall Buildings and Urban Habitat as the fifth tallest building in London.

The first two bolts broke in November when one came right off and landed in the hoarding area after a section of the bolt came loose whilst part of the second bolt came away from the node that connected it to the steel frame and glass structure – albeit with that bolt remaining in place.

Though no one was injured and the company insisted the building was safe, British Lands was forced to cordon off the building to pedestrians at that time.

  • It will be good to see the final report on why they failed.

  • I have seen this before. We had bolts that were not certified to Australian Standards fitted on a site. They were all below par. Expansion and contraction due to thermodynamic change and the fact that these bolts failed destructive testing under the same conditions caused havoc. They snapped the heads off the shank and let go terribly. AS1111 and 1112 are very strict in certification of the purchase of bolts and nuts for structural purposes. They must have certificates in place! Differing grades are allowed and not allowed under certain conditions. What has UK got as an equivalent?

  • Worrying. How can "hydrogen embrittlement" failure be prevented?

  • Hydrogen Embrittlement on Bolts…. I wonder were they Zinc Plated? If done by electro plating to avoid the possibility of high temperature generation of Hydrogen in Hot Dip Galvanizing, (not usually prescribed for High Strength Bolts, because of problems with Hydrogen Embrittlement); there is a problem particularly around the heads of bolts due to turning while tightening and abrasion of the zinc coating, leaving an opening for the creation of a Galvanic Zinc Iron Cell, with the solution being a dilute Carbonic acid caused by the CO2 in the Atmosphere being dissolved in Rainwater. Although the hydrogen evolved in this process, initially ionic, is at low pressure, there is evidence that even at low pressure there can be penetration into steels of high strength, with Embrittlement following.

    Pure Speculation of course. It will be interesting as you say Edward, to see the results of the investigation.

    Another problem due to increased CO2 levels in the Atmosphere and stronger solutions of Carbonic Acid?… Climate Change!

  • No doubt it will be like the instance in China where salt water or sea water was used in the concrete. Very assaulting issue where the attacks on rust become more rapid.

  • They did not use potable water and clean fill? Damn, that is terrible. I bet their cover to reo was small as well. Segregation would have been eminent!

  • Bolts that fail have gone through processes e.g. upsetting bar to make the heads, thread rolling or cutting and heat treatment for high tensile bolts. In my opinion these operations that could be the cause of failure would be more likely than hydrogen cracking.

  • sounds like their may be a problem with the manufacture process. You wouldnt be able to see the full effects of hydrogen embrittlement straight away when the bolt is made, so QA wouldnt notice it, however the enviroment that the bolt were made should be tested. Chances are that these bolts were made in the same place at the same time and there may have been an abundance of hydrogen in the air while the bolts were still hot.
    It would probably pay to check for correlation between the bolts in terms of their manufacture and then asses either testing or replacing any other bolts that match this correlation.

  • I just hope that the investigation results will be announced and not covered up.

  • If it's hydrogen embrittlement , it will not happen on only 3 bolts, the whole batch of bolts have the risk as hydrogen embrittlement is usually caused by manufacture process such as thermal treatment, plating. In those process, the whole batch bolts are treated in same condition.

  • We had a similar problem in India where the customer supplied their own wind turbine tower bolts instead of the specified imported bolts. Their material and processing specs were identical to the imported, but they failed to heat treat them after hot-dip galvanizing. Heads popped soon after tensioning. And so should have the customer's heads.

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