Foster and Partners' new headquarters for the Greater London Authority may have a reduced surface area compared with an equivalent rectangular building (AJ 1.3.01), but there is a high price to be paid for this advantage, namely the complexity and inefficiency of the structural steelwork.
Examination of the photograph that accompanied your report shows eccentricallyloaded sloping columns; hardly the most efficient way of transferring the floor loads down to the foundations.
Each of the circular floors is in a different relationship to the concrete core, so each must have required a separate structural analysis and its own steelwork layout. Inspection on site shows most of the lengths of steel to be of a unique size, with a one-off connector securing it to its neighbour.
Circular floors do not make efficient use of the material when fabricated from steel, because the steel members have to be sized for the greatest span, whereas the geometry determines that many of the spans will be much less than this.
Perhaps Foster and Partners will tell us how much more additional steelwork was required for this project, over an equivalent rectangular building.
Richard Evans, Ewell, Surrey