Prefabrication experiments - 172 - Geometries - 03 - Sunflower swimming pools

Domes have been used too cover architectural space since ancient times. The form resistant shell structures are particularly efficient regarding compressive strain and effective in large spanning structures, as the dome’s rise will increase according to span using geometry to counteract loads. Hemispheric or less than hemispheric domes are structurally pure types that can be assembled by corbelled masonry, thin shell concrete or skeletal filigree components. Skeletal structures such as geodesics are conducive to prefabrication as their circular array geometry facilitates repetitive tessellations of each sector’s composing elements.

The Piscine Tournesol (sunflower swimming pools), a result of France’s large-scale post war building programs during an era of prosperity and growth, was a prime example of unifying simple geometry with prefabrication to serve the nations growing demand for buildings of every type. Architect Bernard Schoeller was responsible for the prototype design that yielded 180 swimming pools in the early 1970s. The dome’s structural system encompassed a circular arrangement of arching girders or joists spread out from a central point. The girders compose 64 equal sectors that make up the rooftop's basic geometry.  Two 60-degree sectors were designed to rotate over rails and reveal a great opening. The resulting 120-degree aperture fashioned a giant doorway relating the pool’s interior to the adjacent landscape. The two large sectors slid underneath the major 240-degree sectors in opposing directions aligning portholes directly beneath each other. The arched joists were attached to a central compression ring and to the circular foundation wall acting as an abutment or in this case as a tension ring withstanding any hoop stresses in the lower part of the structure.

Strangely evocative of Futuro houses designed by Matti Suuronen, polyester (glass fibre reinforced hardened resin) panels glazed in a naval inspired gel-coat finish, were affixed to the steel girders. Each panel was a three layer composite sandwiching an expanded phenolic foam core. The panels were essentially the dome’s skin, including exterior and interior surfaces, transferring compressive stresses through the girders while the hoop stresses were contained by simple horizontal bracing between the girders. The large spanning structures covered a 35-meter diameter rising 6 meters above the water level. The plastic panels pierced with rectangular porthole type windows reinforce the dome’s long-established artificial sky reference. 

Aerial views showing the great opening