Civil Engineering March 2021 | Vol 29 No 2

1. Main waterpolo swimming pool Q Q 28 × 25 × 2.3 m deep tiled heated pool Q Q 25 m pool with first class school waterpolo capabilities Q Q 10 swimming lanes built to FINA specifications Q Q Extended heating (allowing for six weeks extended use either side of summer). 2. Swimming, waterpolo training, and learn-to-swim pool Q Q 12 × 25 × 2.3 m deep tiled heated pool with 3 m wide learn-to-swim lane of varying depth between 0.5 and 1 m Q Q 25 m pool with waterpolo training capabilities Q Q Five swimming lanes built to FINA specifications Q Q Double safety lane and full depth tensioned safety net between learn-to-swim lane and standard pool Q Q Year-round heating. WCSE undertook to design a fully reinforced concrete (RC) shell for both pools to provide a robust and durable structure to which WDI would apply all the necessary finishing and filtration re- quirements. Upfront design co-ordination and discussion on the aggressive corrosive nature of the treated pool water was debated, as well as the best waterproofing methods to be used for such large, tiled pools. This resulted in the following design solution: Q Q High strength 40 MPa concrete for durability with Penetron waterproofing additive. Q Q Increased concrete cover at the pool face of 60 mm. Q Q Design the 250 mm thick RC shell to a maximum crack width of 0.30 mm to BS 8007 using closely spaced small diameter bars. Q Q Cast the inner pool surfaces to a high degree of accuracy to ensure the stringent final pool dimensions. Q Q Allow for and co-ordinate the filtration system box-outs in the initial casts that could be treated with Penetron joint details and infill requirements to ensure watertightness. Large, modern pools such as these are costly due to the high quality imported tiled finish, the high accuracy of the works, and the integrated complex automated filtration, chemical dosing, and cleaning systems. A waterproof concrete shell complimented this technology to ensure that the core of the facility was an integrated and appropriate design solution that would provide may years of service. FEATURE ROOF The architect envisaged a feature roof that would span 38 m over the pools and connect the new eastern double storey block to the original northern entrance and seating area. The concept called for the stepped apex, of consistent height above the pools, to slide on plan by 20 m over the 56 m length of the roof, or 360 mm shift per metre length. The architectural intent of the space required a slim neat structural solution to enhance the arena. Through several conceptual iterations, the design for the feature roof was chosen as a complimentary combination of structural steelwork and reinforced concrete elements. The long-span steel rafters required a high strength-to-weight ratio and fabrication versatility due to the stepping apex line. The roof was to be a focal point and the desire was for a sleek elegant solution that did not resemble a trussed “busy” roofscape. To provide this, portalised structural steel plate girders (720 × 300 × 137 kg/m I-sections) were chosen for the non-identical rafters. Through collaborative verification design between WCSE and The Structural Workshop, the steel design of the roof was final- ised. This included circular hollow section braced bays and the sheeting support criteria for the double-curved sheeted surface. The cold rolled purlins were set out to enable the use of standard concealed fixed sheeting – Zip-Tek 420 sheeting by GRS. The converging layout of these purlins was left exposed to create intriguing lines to the internal surface of the roof together with the underside of the white Lambdaboard insulation. The new eastern block, housing the changing rooms, filtra- tion, and dosing plant room at ground level and a viewing area and heat-pump plant room on the first floor, provided a solid element from which to support the long span roof from this side. The block was regular along the length of the building, making it an ideal element to provide east-west stability to the roof. To create a unique and contrasting feature to the lighter and slimmer long span roof, a feature “diving” architecturally exposed RC column and cantilevering beam was proposed for the internal support of the roof rafters. Behind these, and over the eastern block, standard high quality RC beams and external columns completed the eastern portalised support frames. These frame elements were repeated along the length of the building on a grid at a typical spacing of 6 m. Each eastern frame consisted of: Q Q 400 mm wide special smooth portal frames of 50 MPa con- crete with a height above ground floor of 8 m to 9.245 m. Q Q Feature “diving” column varying in width from 1 000 mm to 1 200 mm with a 5.195 m long cantilevering beam over the eastern edge of the pools with a 600 mm long end seat for the plate girder rafter vertical shear load. 26 March 2021 Civil Engineering Large pool base reinforcement and first western roof column cast (courtesy of WCSE) The existing pool site showing the original 1927 north entrance (courtesy of WCSE)