To provide the clear spaces required for the pool halls, various building- form options were considered. The solution adopted - intended to complement the clean lines and surfaces of the pool halls - is of steel roof trusses formed in circular hollow sections. In the main pool hall, trusses with a depth of 2m and a clear span of 32m, were spliced at third points to facilitate transport and provide a camber. The smaller area of the warm- up pool and cafe/bar have trusses 1m deep, spanning 15m. To give a clear view between the two pools, the roof trusses are supported by a deep truss, spanning 23m, again spliced for transport.
All the roof trusses have a tee section welded full length on the top boom, to en-able direct fixing of the structural roof deck which spans typically 4.8m supporting the roof build-up.
The entire steel frame is hot-dipped galvanised to provide long-term durability; and the exposed steelwork has a painted finish, so maintenance is required only for aesthetic purposes.
The new pool building partly overlays the footprint of the Victorian baths demolished in the first phase of the works. This, coupled with the generally low bearing capacity of the upper soil layer and the high water table, led to the adoption of piled foundations to support the superstructure and reduce the likelihood of differential settlement with the refurbished dry-sports centre. Continuous-flight auger piles were selected as being least disruptive to the local inhabitants or adjacent structures.
Vibro stone-column ground improvement has been used to gain sufficient bearing capacity and control settlements under the pool tanks, which bear at approximately original ground levels. This also enabled the use of loose tipped fill material to the cafe area to raise levels to match the existing building.
Jonathan Apted, Whitby Bird & Partners