GREEN POINT STATIUM

The stadium will contain 68,000 seats for the World Cup. 55,000 Seats will remain permanent and 15,000 modular seats will be re-used in the deconstruction of the existing Green Point Stadium and other social investment opportunities, leaving opportunities for corporate suites to be retrofitted.

The stadium architecture focuses on the exterior appearance as well as on the user experience for the visitor once inside the stadium bowl. The exterior appearance is largely defined by a sweeping silhouette, not to be in competition with the horizontal datum line of Table Mountain, and the façade, made of a stretched fibre-glass mesh and designed as an articulated surface that makes the building appear almost scaleless.

The roof is designed as suspended roof plane. It focuses attention downwards onto the playing field. At the same time, the underside of the roof surface, hovering above the spectators, operates in a way similar to the façade. The translucent mesh skin under the steel cable and truss structure will act as a luminous disc during days of sunlight and will transmit the colour and atmosphere of the day into the stadium interior. The double skin design of the roof further makes it possible to accommodate (unsightly) services therein and, for example, avoid the use of pylons for the floodlighting. It fulfils an important function as far as noise attenuation is concerned. The roof structure is designed as an acoustic “body” with its own internal volume. The principle of utilising the air space inside the body of the roof as a noise buffer is one of the compelling simple and active design principles applied to the stadium. The key to this principle is the requirement that the “inner” (lower) and “outer” (upper) surface of the roof structure must have different densities and therefore display different acoustic performance characteristics.

The current design foresees and ETFE (fibreglass-like) cloth membrane, which is partly permeable. This “breathing” softer inner skin disperses sound waves and, since it is not a hard surface, absorbs sound into the body of the roof. The outer (top) skin is currently designed and budgeted as a fixed glass skin, which provides a hard resonant surface which reflects sound waves back into the body of the roof. Through the sloping surface of the roof, sound waves are diffracted back against the soft inner skin membrane, where they are further dispersed.

http://en.wikipedia.org/wiki/Green_Point_Stadium