BAM worked with structural engineer Ramboll to develop the design for the double-height steel truss that rings the perimeter of the upper two storeys. To achieve the stiffness required steels of different thicknesses were used dependent on the loads the beams had to carry. The steels varied in thickness from 10 mm to 55 mm.
On the north of the facade, two concrete blocks stand 43.2 metres apart, and it was here that the frame was subject to the greatest stress and subject to the highest levels of deflection. A 10-tonne column was inserted as a support, but still left a 28.8-metre span requiring large amounts of steel to reach the required stiffness.
Some of the steel beams had to be cut and replacement pieces welded in place on-site. The thickness meant some connections required 36 rounds of welding. Then the steelwork contractor went into administration. BAM stepped in and took over the package.
Clad to appear as one unified building, the lower levels consist of four concrete blocks. A bespoke cladding system was developed that could cope with the higher levels of deflection. BAM worked with curtain wall contractor Alucraft and glazing manufacturer Schüco to develop a system that could perform under these conditions. This high-spec cladding was then used across the whole building as it worked out cheaper than two separate systems.
Simon referred the work to BAM’s in-house technical services team to check all the calculations. “This is something we often do when there are several parties involved, to check the co-ordination. If something goes wrong, there can be a lot of finger-pointing, which can delay the project.”