Umbrella structures
In umbrella or tree structures, the roof cantilevers from a central column.
The final option for consideration is the umbrella or tree structure in which the roof cantilevers from a central column and can be repeated and joined to other similar assemblies at each or any side to form a continuous structure.
Perhaps the best known example of this is Stansted Airport by Foster Associates. Here, a series of umbrellas, or 'steel trees' as they are known, are arranged on a 36m grid to provide an impressive terminal space measuring 198m x 198m.
The 'trees', which are 21m tall, consist of a cluster of 457mm diameter steel tubes which branch out at the 13m high level to support a shallow dome covering an area of 18mx18m.
A more literal approach to steel trees was taken in a design by Chris Wilkinson Architects with Anthony Hunt Associates for a glass roof to a courtyard for Willis Faber in 1986. Here the structure more closely followed the 'tree' model with the steel columns 'branching' out at higher levels to support the roof purling. This was made possible by the sheltered location which eliminated the horizontal wind forces.
