London has many fascinating structures, from Tower Bridge to the London Eye. However, one of the most recent engineering wonders gracing the city’s skyline is Norman Foster’s 30 St Mary Axe, also informally known as the Gherkin or Swiss Re Building.
30 St Mary Axe is located in the City of London’s main financial district. It was opened on 28 April 2004 to many comments about its phallic appearance. However, the tapering profile was not only an aesthetic selection; it is critical to the energy efficiency of the building.
Sustainable London Skyscraper: The Gherkin
When the Gherkin opened, experts said that it raised the standard for sustainability in skyscrapers. If you happen to visit a tourism office in London or any museum, you will see Gherkin's photographs amongst photos of London.
The design for 30 St Mary Axe was actually developed from ideas that were used in the Climatroffice design by Buckminster Fuller in the 1970s. This building was never constructed, but it was supposed to be a free-form glass skin which allowed the building to have its own microclimate. It would have been very difficult in the 1970s to design and build such a complex structure. However, thirty years later, Foster was able to use advanced parametric modeling to design 30 St Mary Axe whose final design is very reminiscent of the Climatroffice design.
Parametric Modeling’s Role in the Design
Parametric modeling was originally used in the aerospace and automotive industries to design complex curved forms. The 3D modeling process allows any element of a model to be modified easily because each element is linked with a mathematical equation. If one element is changed, the other linking elements are automatically recreated.
Although the Gherkin has an overall curved glass shape, there is actually only one piece of curved glass used in the entire construction of the building. It is the cap at the very top of the structure. The software, which was developed by Bentley Systems, that was used to create the parametric model, was also used to change the individual curved glass elements into flat panels. This technique allowed the building to retain its overall complex form and curved look but also allowed it to be cost effective to construct.
The Gherkin is 180 meters tall and has 40 floors. It is the sixth tallest building in London. It was designed by Norman Foster, Ken Shuttleworth, and engineers from Arup. Skanska was responsible for the construction which took place between 2001 and 2004. It was built to home the UK operations of Swiss Re who are still the building’s primary occupant. Its design has moved sustainability forward in the construction industry and has been copied in other buildings, including Foster’s Hearst Tower in New York.
This unique structure has been admired and criticized in the press. It was declared as the most admired new building in the world in December 2005, in a survey published by 2006 BD World Architecture 200. It was also voted one of the five ugliest buildings in London in June 2006 by viewers of the BBC London News. This building has earned good reviews and bad reviews simultaneously.
Advances in Architectural Engineering
In addition to the modeling technique being state of the art, the finished design also actually moved architectural engineering forward. The Gherkin was built on the former site of the Baltic Exchange, which was structurally damaged on 10 April 1992, by a Provisional IRA bomb. The site is small. The tapered designed allows the building to appear sleeker than a conventional rectangular skyscraper. The slim base and top also reduce reflections and improve transparency, and the floor-to-ceiling windows improve daylight penetration over a conventional building.
The building’s shape also means that it does not need extra reinforcements to add stiffness to resist wind load. The shape of the structure provides the stiffness required. To perfect the shape, wind tunnel tests were performed on a model of the structure. They showed that wind deflected to ground level was reduced and overall wind conditions in the area surrounding the building were improved. The overall stiffness of the structure and the diagonal braces at ground level means that the floor space inside the building is column free.
The energy consumption of the building is 50% less than a typical skyscraper. The building is able to achieve this because of the "diagrid" structure, a grid of diagonally interlocking steel elements used in its construction. Each successive floor is offset so that a spiral atrium is created. Overall six shafts are created by gaps in each floor that serve as a ventilation system. The shafts allow the office space to be insulated with a thin layer of air, similar to the principle of double glazing. Warm air is circulated out of the building during the warmer months and into the building during winter.