Sydney's Spherical Shells

The Sydney Opera House in Australia is a spectacular urban sculpture, perched on the tip of a narrow peninsula jutting into Sydney Harbor.

Designed by Danish architect Jørn Utzon and inaugurated in 1973, the structure consists of three groups of interlocking, vaulted "shells," which cover two main performance areas and a restaurant, set on a vast platform.

Interestingly, the precise geometry of the concrete shells of the Sydney Opera House was not specified in the original concept for the complex. Moreover, each shell was a different size. Initially, the thought was that they could be based on parabolas, but engineers were unable to come up with an economic way to produce the shells either by pouring concrete into formwork on site or by casting concrete forms that would then be transported to the site.

The design team considered a variety of shapes, including schemes with circular ribs or ellipsoids. In the end, the solution was to create the shells out of sections of a sphere. It allowed for arches of varying length to be cast from the same mold, and for arch segments of common length to be placed next to each other.

The complete shell structure required about 2,400 precast ribs and 4,000 roof panels, produced at an on-site factory. The roof was then covered with more than a million glazed ceramic tiles.

One of the architectural wonders of the world, the Sydney Opera House was designated a UNESCO World Heritage site in 2007.

Photo by I. Peterson