Construction of Australia's "billowing sails" Opera House has followed an entirely unorthodox pattern. Designed by a young Danish architect, Jorn Utzon, the drawings were almost never submitted because he thought it would be useless. The assessing committee, however, recognized the originality of the concept expressed, and also its perfect suitability for the site. Construction was planned in three stages. Stage 1 covered the terraced base; stage 2 is the shell construction; and stage 3 will be the finishing and fitting operations. A large part of the building is supported on some 700, 3 foot diameter, cased bored piers. The work was difficult because of tides. The presence of the sea water also meant that the whole structure below ground level had to be built as a number of waterproof reinforced-concrete compartments. The slab and steps of the concourse cover some 75,000 square feet with varying spans up to 164 feet. The slab is surfaced with 6 by 4 foot panels of artificial granite with open joints between them to carry away rainwater. The sides shells were erected first by locating precast segments on top of each arch pedestal and stressed to it permanently. Further segments were then placed until the arches meet at the central plane of the shell between 70 to 150 feet above the tops of the foundation columns. When all four arches of a unit were competed and post-tensioned, a precast crown piece was inserted and site-cast in place. The arches braced in pairs either side of the auditorium center line by precast members that act as beam columns. In addition, there is a main brace between the arches parallel the auditorium axis. The main shells are built out rib by rib, from the side shells. As the segments for a rib are positioned they are jointed with an epoxy resin to transfer shear and stressing loads. The last step is to locate a precast keying ridge continuous. The ridge piece is first post-tensioned into the ribs by means of three cables. During erection each rib is allowed to deflect independently, until finally they are post-tensioned together laterally through thin site-cast joints.