Computers and the Sydney Opera House

Zofia Trafas White, Co-Curator of Engineering the World: Ove Arup and the Philosophy of Total Design, discusses the pioneering use of computers on the Sydney Opera House project.

In early 1957, the Danish architect Jørn Utzon won the competition for the Sydney Opera House design on the strength of powerful drawings — an expressive charcoal sketch showing a building with a dramatic roof composed of gravity-defying curves. His design had no engineering consultation upon submission. On hearing of the appointment in February, Ove Arup sent Utzon a personal letter suggesting they collaborate. By March, the Arup engineering firm was formally appointed to the project team. Utzon’s ambitious vision for the shape of the roof posed a huge number of structural engineering challenges. Many contemporary critics in the profession considered it impossible to build. The geometrically undefined curves of the roof needed to be developed in order for the building to be built. The search for a solution was driven by a close creative partnership between the architect and engineer team. In the quest to maintain Utzon’s original vision, Arup engineers developed as many as 12 different versions of a concrete roof design between 1957 and 1963. The roof evolved from the freeform shape of the architect’s original sketch to the spherical geometry of the final design.

Jørn Utzon and Ove Arup with project engineer Povl Ahm discussing the roof structure in Utzon’s studio, 1959, Hellebaek, Denmark. © Yuzo Mikami/Courtesy Arup

The evolution of the Opera House roof design was guided by many years of rigorous structural analysis. Finding a buildable version of the challenging shape called for new techniques for calculation and testing. Arup engineers conducted a series of model tests to assess the stability of various versions of the roof design. These included stress distribution tests conducted on a large Perspex model of the roof at the Structural Laboratory in Southampton University, as well as a series of tests on models in wind tunnels at the National Physical Laboratory in Teddington and Southampton University.

Model of Sydney Opera House roof undergoing stress distribution testing at Southampton University, 1960. © Henk Snoek/Courtesy Arup

Assessing each successive design scheme for the roof, along with processing results from the model tests, required an enormous amount of calculation and analytical work. Gifted mathematicians at Arup, like the engineer Ronald Jenkins, led the work up to 1961, providing the team with numerical equations for the structural analysis. The complexity of the evolving design however demanded regular revisions. Design changes in one area of the roof resulted in large amounts of analysis being superseded. To cope with the volume and difficulty of calculation work, Arup engineers turned to computer power on a scale never before employed.

It is important to note that until the Sydney Opera House project, engineers working in the building industry did not use computers for calculations. Structural analysis calculations were conducted manually, with the aid of a variety of tools, such as slide rules and tables of logarithms. Small mechanical, hand-cranked devices like the Curta calculator, or the FACIT calculating machine were also used. Arup’s pioneering application of computers on the Sydney Opera project pushed the limits of contemporary technology and revolutionised engineering practice.

Ferranti Pegasus Mark 1 computer, 1957. © Mary Evans Picture Library/Alamy Stock Photo

The Ferranti Pegasus Mark 1 computer from 1957 was the first computer used on the Sydney Opera House project. It was one of the earliest commercially produced computers available in the UK, made by the Manchester-based electronics manufacturer Ferranti Ltd, a company that was at the forefront of the UK’s emerging computer industry in the 1950s. Use of computers was not yet widespread — striking sales figures reveal that as few as 26 Pegasus computers were produced and sold in 1956. Arup did not own their own machine and instead hired use of the Pegasus computer by the hour at Ferranti’s London Headquarters in Newman Street, around the corner from the firm’s Fitzroy Street base. They also had access to a Pegasus computer owned by Southampton University — whose research department was already involved in the Opera House project.

Computer technology was still in early days and Arup engineers, with the help of specialist programmers from Ferranti, wrote their own software programmes for analysing the roof design. Each run on the Pegasus computer would take between 12 and 14 hours, in addition to weeks of data preparation, and later interpretation of the results. While this may seem staggeringly slow to us computer users today, it was nonetheless a breakthrough pace of work at the time. Computer calculations became integral to structural design work on the roof, as well as later stages of fabrication and construction planning. Estimates of the computer hours used on the project up to 1962 reveal that if done manually, the calculation work would have taken Arup engineers a further ten years. The Opera House could simply not have been built without the help of computers.

Evidence of this incredible calculations story remains in the Arup Archive today. The Sydney Opera House project archive, ‘Job 1112’ as it is known, comprises hundreds of boxes of manila folders filled with thousands of sheets of manual and computer calculations dating from 1958 to 1963 — their sheer volume a testament to the enormity of the task that the engineers were charged with. A sample of these original calculation documents, together with the 1957 Ferranti Pegasus computer and an array of models, photographs and films documenting the evolution and testing of the design are on display in Engineering the World.

The use of the Pegasus on the Sydney Opera House was one of the first times computers were used on a large-scale construction project — a game-changing moment in the history of architecture and engineering in the 20th century, and one that is particularly meaningful in the context of the ubiquity of computers in design processes today.

Robert Baudin, Sydney Opera House under construction, 1966. © Robert Baudin for Hornibrook Ltd, courtesy Australian Air Photos

Following the Sydney Opera House project, computers continued to have an impact on the work of the Arup firm. From the mid-1960s on, Arup began buying their own computers and formed a dedicated computer group to continue experimenting with applying computer technology to various design projects. The firm’s dedicated software design arm, Oasys, also emerged from this group. However as David Taffs, leader of Arup’s first computing department, later recalled, the cautionary Arup maxim for using computers remained throughout those early years:

'If you don’t know the order of magnitude of the answer, don’t use the computer.'

A sobering note that perhaps remains relevant today, acknowledging that computers should never ultimately replace an engineer’s confidence and ability to test and assess a design problem.