In plan the bus station roof canopy is an ellipse, supported by a series of tree-like, three-branched steel columns. It is made of cast in-situ concrete, chosen for its ability to act as a plate, allowing the column supports to be positioned at irregular intervals between curved bus lanes.
The roof canopy cambers upwards to the centre, a rise of 450mm, to eliminate any perception of sagging and to direct rainwater to eight outlets set in the perimeter branches of the column trees which discharge within the columns.Only 325mm deep and made of lightweight concrete, the canopy is stiffened at the perimeter by a 300mm wide,550mm deep beam of dense concrete, with a flat soffit and a tapered edge.
While slender and unobtrusive, the tree-like form of the columns gave designers the flexibility to position them to suit the circulation and traffic layout.
Each primary column, a 323mm diameter CHS, supports three triangular branches of welded steel plate; they are braced within the slab by 152 x 30mm UC tie beams.Columns and branch assemblies were fabricated as separate elements and welded together on site.Each column supports three uplighters.
A series of 5m diameter hooded cowls, open to the sky and facing south, run over the bus lanes, modifying natural light and providing high-level ventilation.Their upstands, of dense concrete, help to stiffen the slab.A series of smaller 2m diameter rooflights, glazed with laminated glass, light the pedestrian islands.
The canopy is covered by a low-maintenance sedum roof to protect the waterproof membrane from UV light and reduce dust and pollution.