Arup engineered this Jean-Francois Koenig designed office building. The main features of its unusual form are:
- The floors: a set of flat slabs plus the curved auditoria slab enclosed within the ellipse of the building
- The four legs: which provide the necessary resistance to vertical and lateral forces acting on the structure
- The elliptical skin: consists of curved concrete columns/walls from level 4 up to level 7 and a steel roof structure from level 7 upwards. The cladding is precast-concrete panels.
All upper floors are ordinary flat slabs spanning on to a grid of large diameter circular columns.
The external elliptical skin acts as a series of curved columns, providing both lateral stability and support to the floors. To enable a column free space in the main auditorium, the frame includes transfer structures between levels 4 and 5.
Similarly, the building entrances are kept column free by means of steeply raking columns picking up one of the transfer structures. Bracing and core walls, supplemented by large diameter columns, provide lateral stability.
How Oasys proved invaluable
The structure was modelled in Oasys GSA and was divided into four main areas of investigation:
- An overall model for checking the lateral stability of the building by frame action under 275 km/h winds
- A series of refined F.E models for each floor slab
- A detailed model of the arched steel roof
- Detailed F.E models of the transfer walls on Level 4 and the shear wall below the curved Level 2 slab (picking up the inclined columns)