1969 Building
When completed in 1969, the building at 122 Leadenhall Street was 54 m (177 ft) tall with 14 storeys above and three storeys under ground. It was originally designed as a pair with the Commercial Union headquarters (now called St. Helen's) by the architects Gollins Melvin Ward Partnership. The two buildings have a central compressional concrete core and have suspended floors which hang using the steel 'chords' visible on the exterior of the building, which are hung from power trusses at the top of the building (and in the case of No. 1 Undershaft, a further central power-truss). It is an example of a tension structure; at the time, it was considered one of the most complex glass-fronted buildings in the United Kingdom. The architect acknowledged the influence of Mies van der Rohe.
The building was extensively damaged by an IRA bomb in the early-1990s and subsequently had to be reclad. It was occupied by various tenants until November 2006, including the Italian International Bank and Calyon.
In 2007-08, the building was demolished to make way for a new development designed by Richard Rogers. The demolition was undertaken by McGee Group Ltd., with Bovis Lend Lease acting as construction manager. The contract value was £16 million. The first phase of demolition was conventional: after securing the site, the contractors performed a soft strip of the interior and an asbestos survey prior to demolishing the low level structures up to podium level. After this, the suspended structure of the building required an unconventional demolition approach that successively dismantled each office floor from the lowest upwards. To achieve this, the contractors installed a structural deck that acted both as a work platform for the demolition work and as a safety barrier. This was jacked upwards as each successive office floor was removed. When all the office floors and upper support trusses had been removed, the concrete core was de-stressed and demolished. Concurrently, the 25,000 cubic metre basement was propped and excavated. The contract took just over two years to complete.
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