A glazed roof of steel trusses
Restricted on all sides by existing buildings, the new station concourse is covered by a glazed rectangular 'box-lid' roof of twelve ridge and furrow trusses. The west end lies parallel to the terminal arch of Brunel's railway shed.
The trusses span 20m to rest at each end on a 4m deep perimeter steel truss which is supported by stanchions encased in white precast concrete with an acid etched finish by Trent Concrete.
Between the trusses run structural gutters, of folded steel plate stiffened by 75mm steel ribs, which form maintenance walkways.
A 193mm diameter chs spine beam forms the apex of each truss; pairs of 89mm diameter chs outriggers, welded to each side of the spine beam, slope down to create the pitch of the roof. They terminate in steel castings with forked ends which connect them to the gutter ribs.
The lower booms of the trusses vary in length - from 2.5m at the centre to 1.3m at the ends - to reflect the bending moment force. They consist of a series of tensioned 40mm steel rods, connected to the spine beam by tapered 'stiletto' struts, and connected to the gutter ribs by a lower pair of outriggers. The outriggers and rods are connected by a complex stainless steel casting, cast in sand by Goodwin Steel Castings and welded to the bottom of each stiletto.
The painted steel glazing frames are propped at their edges by stubs welded to the top of the spine beams, so that they cannot be perceived. The frames contain clear toughened and laminated double-glazed units. A series of external louvre panels are fixed above the south-west faces to reduce solar gain.