A stand with precast units and shear walls
The lower tier of the new stand is formed of a series of structural stepped precast 'staircase'units.
The units and the walls of the vomitories that give access to them were cast with a mix of white concrete incorporating Derbyshire spar aggregate.
The backs of the lower tier units rest on beams spanning between a series of 14 precast concrete shear walls which stand at the rear of the stand.Each shear wall is 3m wide and more than 11m high; they are generally spaced at 7.6m centres. To maintain accuracy of fit and alignment, each shear wall was match-cast in two paired units with steel shoe connectors;
these were then welded together on site.
The shear walls were cast using Spanish Dolomite coarse and fine aggregate, which introduces a sparkle into the surface of the concrete.
The main staircases at the rear of the stand were cast with coloured concrete, using Cree Town coarse aggregate with Lee Moor fines.The mix contrasts with the Spanish Dolomite and gives a durable non-slip surface to the main escape routes.
Lightweight grey concrete was used for the upper terrace units to reduce dead load. The overall weight saving is greater than pro-rata as the depth required to produce the same level of fire resistance is less for lightweight concrete.
The use of precast units solved a serious problem - having a restricted site yet with a water table that would not permit the development of a basement.
In addition, the use of precast speeded up the construction process; installation was simpler and there was no need to use wet trades - the soffits of the units are exposed to form the ceiling.