The Opera House Project

Chapter 11: The Spherical Solution (Part 1)

By the middle of 1961, almost three years had passed since Utzon had put a plastic ruler on a table and bent it to the forms he wanted expressed in the roof. It was this act which determined the shape of the roof in the Red Book. Three years – yet an adequate engineering solution had still not been presented. For all involved, resolution of the issue was now pressing.

Three problems complicated the design process from the beginning. All revolved around being absolutely faithful to Utzon's original conception of the shape of the roof.

Firstly, despite a significant change in form between the submission sketches in 1957 and The Red Book in 1958, each shell remained unique, precluding prefabrication of the form, which had implications for both ease of construction and cost.

Almost all buildings apply the principle of prefabrication. It is most easily observed in office buildings. Structures which feature rectangular panels, with repeating dimensions of interior spaces and mouldings mean that construction techniques can also be repeated – making the building process both easier and more efficient.

It is a testament to Utzon's approach, that in design and engineering his ideas constantly pushed at the boundaries of the possible.

From the beginning of their collaboration, Ove Arup gently encouraged Utzon to pursue a geometry that would allow for repetition and therefore prefabrication. But Utzon remained convinced and encouraged in his conviction by Arup's partner, Ronald Jankins, that a shell structure with the smooth finish of an egg would be possible, despite the unique form of each shell.

Thin shell structures were the form of his original sketches and very much favoured by leading architects and engineers at the time. Eero Saarinen, Felix Candela and Pier Luigi Nervi had already used concrete shell membranes in world-renowned structures.

The first problem led to another: whether to approach the roof as a shell or a rib structure. A ribbed structure would provide a very different interior to the smooth concave surfaces imagined in the original sketches, a surface that Utzon had lined with gold leaf in his competition sketches, hinting at the bold use of colour he would later use in his designs.

By 1961, Utzon had long been impressed with Ove Arup's design of the concourse beams, which were already being constructed and demonstrating perfectly the method of prefabrication whilst also, to Utzon's mind, revealing a genuine 'honesty' of form.

What Utzon meant by 'honesty' was that the structure of the building couldn't be a lie; it needed to express its function. The idea of a massive shell structure would be unacceptable if it were to be built as a double skin of concrete that hid a steel structure inside.

This was essentially the solution that evolved through a series of iterations by the lead engineer, Ronald Jenkins and his team since 1959 as they attempted to find the solution that would support Utzon's smooth shell design.

The concourse beams impressed Utzon because they so beautifully expressed their function. He felt that a steel form, hidden between concrete skin on either side, would do the opposite. The finished roof would be a false expression of the original idea.

As early as 1958, when Ove Arup was principal engineer on the project, he had suggested that the soffits of the shells, their interior surface, be ribbed to further strengthen and articulate them. But this design was found by Jenkins' team to be too weak to withstand various forces acting on the structure.

By June 1961, Ronald Jenkins was dismissed from the opera house project by Arup himself. Both men were frustrated that an appropriate engineering solution to Utzon's forms had still not been found. Hugo Mollman, Jenkins' associate, resigned in protest.

Both Jenkins and Mollman had been strongly committed to the parabolic approaches in their attempts to express Utzon's shells, an approach that was not unkindly, but consistently, rejected by Utzon. Ronald Jenkins, a renowned mathematician and recognised expert on shell structure, never worked again.

With Jenkins and Mollman gone, Arup assigned Jack Zunz to take over the approach to the roof and oversee the completion of Stage One. Zunz rapidly reorganised the team and suggested a new structural design that separated the shells into three structures.

Arup and Zunz also resurrected the ribbed approach from 1958, pursuing the two options of a double-skinned shell structure and the ribbed form. Both continued to treat the form of Utzon's shells as unalterable. Neither qualified for a prefabricated approach.

In late August 1961, Utzon visited Arup and Zunz at the Fitzroy Street offices where Zunz presented the two proposals. Knowing in advance Utzon's unease about the double-skinned shell approach, and his appreciation of the concourse beams, it was no surprise that Utzon chose the ribbed approach, which would dramatically express the roof's function through the exposed concrete form of the interior roofs.

By all accounts, Utzon was adamant about the decision.

Three years of work by Arup engineers was being discarded, yet a point had been reached which enabled Utzon to make his most pivotal discovery in the design of Sydney Opera House.