Leadenhall failures confirmed as hydrogen embrittlement
12 March 2015
Last autumn two ‘megabolts’ fractured in the structure of newly constructed 122 Leadenhall Street, in the City of London. In January British Land released limited information from the subsequent investigation – including confirmation that a third bolt had broken.
Nicknamed the ‘Cheesegrater’ for its distinctive design, the 224m, 47-floor Leadenhall Building provides some of the most expensive office space in the City of London. Co-developed by British Land and Oxford Buildings, it was designed by architects RSH+P and has been described as “remarkable for the unprecedented scale of its use of a ‘tube’ structural perimeter envelope with an external support core”1. More than 80% of a 16,000 tonne steel structure was prefabricated off-site at specialist steelworks, delivered and then assembled on-site.
The structure is divided into eight sections, each 28m high and comprising seven floors (the first section has five floors). Steel columns and beams are connected by nodes that transfer forces of up to 6,000 tonnes. Threaded steel rods connect all the steel parts. Construction began in 2011 and was completed in June 2014.
Debris from one of the two fractured ‘megabolts’, described as the size of a human arm, fell from the fifth floor. The other fell from the 19th floor within the frame of the building. British Land stressed: “No one was injured in either incident and there is no risk to the structural integrity of the building.” It said: “The design of the structure allows for isolated events of this type and do not affect the structural integrity of the building”. A full investigation was initiated, including examination of the remaining 3,000 bolts.
On 14th January British Land issued a 75 word update on the fractured bolts, at the end of a more detailed statement announcing that architects had taken space in the building and that 70% of space was either let or subject to offer. The update read: “In November 2014, we reported that two bolts had fractured at the building. Investigations undertaken by contractor Laing O’Rourke and structural engineers Arup have now been completed. These confirm that the problem is limited to certain bolts. Arup has also confirmed that there is no adverse effect on the structural integrity of the building.”
British Land also revealed: “A third bolt fractured recently and was captured by precautionary tethering put in place last year.”
“The investigations included site and laboratory testing of the broken bolts and additional bolts on the building. The tests concluded that the bolts had fractured due to a material failure mechanism called hydrogen embrittlement.”
British Land concluded: “As the problem has been identified and is being rectified no further update is scheduled.”
Fastener + Fixing Magazine did request further information. However, British Land declined to answer questions regarding the number of bolts being replaced, the testing methodology or the source of the hydrogen contamination, saying these technical aspects “are a matter for those involved in its construction”. Neither Arup or Laing O’Rourke, however, were prepared to expand on the British Land statement.
British Land did tell F+FM: “We’ve identified that the problem is limited to the bolts and Arup has confirmed that there is no adverse effect on the structural integrity of the building. We’ve also indicated the action we are taking to remedy this and do not believe there are any further implications for the use or availability of the building beyond that already reported, so we’re not scheduling a further update.”
“We are replacing bolts that are in a similar position to those that broke as a precautionary measure. Only megabolts at certain levels of the building are affected, which impact 11 tenanted floors.”
