30 St Mary Axe, widely known informally as “the Gherkin” and previously the Swiss Re Building, is a skyscraper in London’s main financial district, the City of London, completed in December 2003 and opened in April 2004. With 41 floors, the tower is 180 metres (591 ft) tall and stands on a street called St Mary Axe, on the site of the former Baltic Exchange, which was extensively damaged in 1992 by the explosion of a bomb placed by the Provisional IRA.
After the plans to build the Millennium Tower were dropped, 30 St Mary Axe was designed by Norman Foster and Arup engineers, and was erected by Skanska in 2001–2003. The building has become an iconic symbol of London and is one of the city’s most widely recognised examples of modern architecture. Torre Agbar is an architecturally similar building in Barcelona which opened in June 2005.
The building uses energy-saving methods which allow it to use half the power that a similar tower would typically consume. Gaps in each floor create six shafts that serve as a natural ventilation system for the entire building even though required firebreaks on every sixth floor interrupt the “chimney.” The shafts create a giant double glazing effect; air is sandwiched between two layers of glazing and insulates the office space inside.
Architects promote double glazing in residential houses to avoid the inefficient convection of heat, but the tower exploits this effect. The shafts pull warm air out of the building during the summer and warm the building in the winter using passive solar heating. The shafts also allow sunlight to pass through the building, making the work environment more pleasing, and keeping the lighting costs down.
The primary methods for controlling wind-excited sways are to increase the stiffness, or increase damping with tuned/active mass dampers. To a design by Arup, its fully triangulated perimeter structure makes the building sufficiently stiff without any extra reinforcements. Despite its overall curved glass shape, there is only one piece of curved glass on the building—the lens-shaped cap at the very top.
On the building’s top level (the 40th floor), there is a bar for tenants and their guests featuring a 360° view of London. A restaurant operates on the 39th floor, and private dining rooms on the 38th. Whereas most buildings have extensive lift equipment on the roof of the building, this was not possible for the Gherkin, since a bar had been planned for the 40th floor. The architects dealt with this by having the main lift only reach the 34th floor, and then having a push-from-below lift to the 39th floor. There is a marble stairwell and a disabled persons’ lift which leads the visitor up to the bar in the dome.
