This initial sketch and perspective drawing show how engineer Ove Arup planned the complicated construction process involved in assembling the roof of the Sydney Opera House.
When architect Jørn Utzon won the Sydney Opera House competition in January 1957, no one knew how to build the roof structure he had designed. Utzon's original concept showed huge, billowing shells resting on narrow points, but the engineer, Ove Arup, had seen immediately that the shells would not sustain the forces they would generate. Also, they were irregular and could not be defined mathematically. Prefabrication and calculation were both impossible. 'We had no precedent to go on', said Utzon. 'It was like climbing Mount Everest for the first time.' Three years later, when work on site had already started, he found the answer - in an orange. By cutting 'spherical triangles' from the skin, he discovered a regular basis for the irregular forms he wished to create. Arup was then able to design a structure in which a framework of pre-fabricated, tapering ribs of identical curvature would support a thin skin. The idea of frameless shells had been lost, but Utzon's vision could now be realised.