Structural bolts on 11 floors of the Cheesegrater skyscraper in the City of London are to be replaced as a “precautionary measure” following a probe into why two bolts fell from the 47-storey tower in November.
Parts of two of the 3,000 diameter bolts used in the 224m high-rise office structure, – officially known as 122 Leadenhall Street and designed by architect Lord Richard Rogers – broke away, causing the building to be fenced off.
Developer British Land also admitted a third had also broken off – but was caught in safety netting
It is believed the first bolt broke on the 19th floor but stayed within the building’s structure, without hitting the ground – while the second bolt piece plummeted from the fifth floor.
All the bolts have been checked and the investigation found the failures were caused by so-called “hydrogen embrittlement” – growing cracks in the metal caused by the presence of hydrogen in the manufacturing process.
As a precautionary measure British Land’s contractors are replacing bolts in a similar position to those that broke.
British Land said engineers Arup had confirmed there was “no adverse effect on the structural integrity” of the building.
The Cheesegrater is the fourth tallest building in the UK and the 493rd in the world.