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Look Out Below: Why bolts on London’s Cheesegrater tower are dropping to the ground?

The news that a third bolt has fallen from the new Leadenhall Building (popularly known as ‘The Cheesegrater’) in the City of London has caused consternation among those involved, coupled with a surge of interest what’s causing it. This latest incident follows the similar failure of two bolts in November last year, just four months after the building was completed.
“It’s very difficult to do non-destructive testing for bolts that might have tiny cracks because the nature of a bolt is that it has many tiny cracks built into it” – Paul Lambert, technical director of Materials and Corrosion Engineering at Mott MacDonald
One of those events resulted in debris falling from the fifth storey to the pavement below and triggered an investigation by Laing O’Rourke, the main contractor on the scheme, and Arup, the structural engineer. According to a statement released on 15 January by British Land, the joint developer of the 222m-high building, the failures never posed a threat to the structural soundness of the building, and it said a number of bolts, each of which is about as thick as a man’s arm, had been replaced, although it didn’t say how many. The reason for the replacement was that they were suspected of suffering from “hydrogen embrittlement”, a process that lowers the ductility of fasteners. This then raised the question among those observers who were not metallurgists, materials scientists or structural engineers as to what hydrogen embrittlement actually was. The answer is that it is quite scary … Detail via GCR.

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