Mott MacDonald worked alongside South African consultants, Goba, to deliver the structural design. We were primarily responsible for designing the cable-supported roof structure and ensuring that the dynamic response of the 43,500 seat venue did not trigger uncomfortable vibrations under crowd motion.
At 55kg per square metre, the roof of Mbombela Stadium weighs only half as much as the average trussed stadium roof, setting international standards for structural efficiency. Our super lightweight design was in response to a tough brief: our client, Mbombela local municipality, had a restricted £66M budget.
Structural efficiency
The roof is composed of steel trusses. Primary trusses cantilever 40m over seating from concrete piers that surround the stadium bowl. Primary trusses are connected by secondary trusses forming inner and outer rings around the stadium. Spanning between the secondary trusses, tertiary trusses support purlins to which the roof cladding is fixed. Masts and cable stays support the roof.
As the structure grew increasingly lightweight, a key challenge was to resist uplift created by gusting wind, which could have caused the roof to bounce on its supporting cable stays. Mass was added by placing in situ concrete in the walkway at the front of the roof, enabling the weight of structural steel to be pared back. The roof was analysed to ensure it would be robust under the most extreme load cases, including losses of a set of cables or a primary truss.
Ease and safety of construction was achieved by making every element of the roof light enough to be lifted using conventional cranes. Its rectangular shape provides the best view of the pitch.
Mbombela Stadium incorporates world class facilities. It now serves as a multi-purpose sport and events arena with the aim of generating further prosperity and positive social change in the north eastern area of South Africa.