Star jumps: how the diving boards took shape

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ZHA project architect Sara Klomps explains that the distinctive shape of the boards was designed using Rhino 3D modelling software, and a “positive” of the 10m board was cut from Styrofoam using a CNC (computer controlled) router. The Styrofoam shape was then used to create large, heavy-duty fibreglass moulds in 2.5m-high sections.

“This is quite an expensive process but we were able to make all of the moulds from one Styrofoam positive created in the shape of the largest, 10m board,” says Klomps.

By “missing out” one of the lower 2.5m blocks it was possible to create the 7.5m board, and to create the lower boards the team used only the top and “knuckle” moulds. “Although we did, for logistical reasons, require more than just the four basic moulds, they were at least all made from the single original shape,” says Klomps.

The construction technique is evident from the appearance. On the 10m board, for example, it can be seen that the structure has been poured (in situ) in the 2.5m mould sections. The pour lines give the impression that sculpted concrete blocks have been placed one on top of another, even though the knuckle and top sections were poured monolithically for each of the boards.

What visitors to the aquatics centre cannot see is that inside each tower is a surprisingly dense network of reinforcement, for although the boards support only their own weight (and occasionally that of a diver), they cantilever off the ground at an angle and the forces acting upon them are considerable. “As a result they have to be very strong and securely anchored,” says Klomps. “The extra reinforcement also helps to reduce vibration to a minimum, which is one of the requirements from FINA [the body that regulates international competitive swimming]. It is also important that there is minimal settlement over time, because the high board, for example, has to remain exactly 10m from the water – another FINA requirement.”

The reinforcement posed a potential problem, however, with the fear that voids would occur where concrete failed to flow around the dense tangle of steel. “Because of this, we chose a special mix that was able to ease the concrete around the dense reinforcement.”

This was a highly fluid self-compacting mix including 30% GGBS and 10mm carboniferous limestone aggregate. Some 462 tonnes was needed to construct all six boards. “Besides the environmental targets, the GGBS was used to reduce pour temperature and the carboniferous limestone to reduce the coefficient of thermal expansion of the concrete, limiting thermal movement and assisting with crack control.”