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buildings, structures & design; foundations; steel structures
Heron Tower is a new landmark office building in the City of London which is due for completion in February 2011. With 47 storeys above ground and a total height of 232 m, it exceeds Tower 42, which has held the city record for the past 30 years. A steel stability tube structure encloses the office floor plates, carrying vertical and lateral loads to a secant pile wall at ground level, which forms the perimeter of a three-storey basement. This paper describes the construction strategy devised by the designers, with top-down basement construction concurrent with superstructure erection.
The site of Heron Tower has a significant history in the context of the City of London. It is positioned alongside the Bishops Gate of the original Roman London Wall, which dates back nearly 2000 years. Those associations give Heron Tower symbolic significance as a landmark building, which will be recognisable across the landscape of the city.
Today the site is bordered by the nearby conservation area of Middlesex Street and the grade II listed church of St Botolph without Bishopsgate is on the opposite side of the road. Despite the prime city frontage, the site does not infringe on the strategic views of St Paul's Cathedral or the designated areas of London defined to protect St Paul's Heights.
It is an 'island' setting within the exiting street layout, surrounded on four sides with traffic from Houndsditch to the north, Camomile Street to the south, Outwich Street to the east and Bishopsgate to the west. The two buildings that once occupied the site were Bishops House and Kempson House, constructed in 1971 and 1961 respectively, both differing in architectural and structural composition and neither attracting any architectural significance.
The arrangement of the existing buildings was inefficient by today's standards for space demand in the city, with a large proportion of the footprint unoccupied and under utilised. The occupied footprint relative to the public realm was also ineffective, with narrow pavements created between the elevations and the road giving a poor environment for pedestrians. Despite it being on a main route through the city to Liverpool Street station, the predeveloped arrangement was oppressive to pedestrian movements in the immediate vicinity.