The congested site and restricted access posed significant challenges for the construction process. The complexities of party walls, existing subterranean services, archaeological investigations, the retained Coronation House facade and the main walls and foundations of 71 Fenchurch Street, all needed to be taken into consideration. Following the necessary subterranean investigations, the concrete superstructure was founded on piles driven into the underlying London clay, above which a double basement accommodates heavy plant for the building services.
The main office towers consist of an exposed pre-cast concrete frame, combined with insitu concrete infill elements to form a composite structure. This has the advantage of allowing the main structure to act as a braced frame without the need for bracing walls in the cores. The pre-cast system was designed to accommodate the complex geometry, tight tolerances and multiple service penetrations, all of which required meticulous attention to detail during the design and exceptional care in construction.
At the front of the main towers are the lift cores and staircases, each housing four external glass lifts. The lift cores are supported on a slender structural steel frame that derives all of its lateral stability from the main concrete structure. The lift motor rooms, which extend an additional three storeys above the top of the main building, have a fully welded steel frame to provide adequate support for the complex combinations of loads caused by the operation of the lifts and exposure to wind.
RRP also supervised the renovation and refurbishment of 71 Fenchurch Street using specialist contractors for the historic restoration work. The entire rear elevation of the building was demolished to allow for an interface with the new building via a core structure tied to the existing building without introducing any additional load onto it.
The design allows the building to be split into a number of tenancies either on a floor by floor basis, or vertically. 71 Fenchurch Street can also be used as a separate entity if required.
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