30 St Mary Axe (informally known as The Gherkin and previously as the Swiss Re Building) is a commercial skyscraper in London’s primary financial district, the City of London. It was completed in December 2003 and opened in April 2004. With 41 stories, it is 180 meters (591 ft) tall and stands on the former sites of the Baltic Exchange and Chamber of Shipping, which were extensively damaged in 1992 by the explosion of a bomb placed by the Provisional IRA in St Mary Axe, the street from which the tower takes its name.

After plans to build the 92-story Millennium Tower were dropped, 30 St Mary Axe was designed by Sir Norman Foster and Arup Group and it was erected by Skanska, with construction commencing in 2001.

The building has become a recognizable feature of London and is one of the city’s most widely recognized examples of contemporary architecture.

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, which avoids the inefficient convection of heat across the relatively narrow gap between the panes, 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 apex.

On the building’s top level (the 40th floor), there is a bar for tenants and their guests, featuring a panoramic 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 are a marble stairwell and a disabled persons’ lift which leads the visitor up to the bar in the dome.

The building is visible over long distances: From the north, for instance, it can be seen from the M11 motorway, some 32 kilometers (20 mi) away, while to the west it can be seen from the statue of George III in Windsor Great Park.

[Excerpts from Wikipedia]