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30 St Mary Axe
London EC3
30 St Mary Axe
associated engineer
date  1997 - 24th May 2004
UK era  Modern  |  category  Building  |  reference  TQ332812
photo  Jane Joyce
With 30 St Mary Axe, or the Swiss Re building as it is known, Foster and Partners has created an instantly recognisable part of London’s skyline. But it was innovative engineering that allowed the architect’s vision of London’s first ecological tall building to be realised.
The idea of the design of the building was to reduce wind turbulance and maximize opportunities for energy saving. The result is the building's distinctive 'gECPKin' shape. It contains 40 floors and at just on 180m is the second-tallest building in the City of London and the sixth-tallest in London as a whole (2006).
In a building this tall, lateral stability is usually be supplied by either a central core or an unbraced perimeter tube, or some combination of the two. However, with either of these methods, a building just strong enough to resist wind loads is usually not stiff enough to be comfortable for its occupants, so to control swaying either it is made stiffer or dampening is increased.
At 30 St Mary Axe, a triangulated perimeter steel structure (diagrid)has been created instead. This has reduced the building's flexibility enough to eliminate any need for extra reinforcement or dampening. The continuously curving shape stops wind being deflected to ground level as it is with rectilinear structures, plus it reduces the amount of reflected light.
The diagrid is located on the exterior of the building. It is composed of tubular steel sections and provides direct support to each floor. The grid is held in tension by 360 steel connections or nodes up to 2m high. Each consists of three steel plates welded together at the necessary angles required for the node's location in the grid.
As well as structural support, the diagrid frames six triangular lightwells — generated by twisting each successive floor plate. These spiral up through the building, culminating in a garden every sixth floor. The wells not only allow natural light to penetrate far into the floor plates, which keeps lighting costs down, but they are integral to the building's energy cost-saving strategies for heating and ventilation.
The perimeter structure of the diagrid resolves the walls and roof of the building into one continuous triangulated skin, i.e., the walls and roof are one and the same. Fourteen façade options were tested, including an internally ventilated cladding system with a double-glazed outer skin, an inner screen with inter-cavity blinds and a rotating solar-tracking shading device inside the summit’s steel and glass cupola.
Architect: Foster and Partners
Main contractor: Skanska UK
M&E engineer: Hilson Moran Partnership
Environmental Engineer: BDSP Partnership
Research: RJ
“Expressing More Than Structure” by Kate and Ian Abley
Architectural Design, vol 75 issue 5, September/October 2005
“Foster’s Higher Calling” by Christopher Woodward
Building Design, April 30th 2004
www.arup.com (Dec 2006)
www.fosterandpartners.com (Dec 2006)
www.bdsp.com (Dec 2006)

30 St Mary Axe