Shell concrete

In 1919 Dr. Walter Bauersfeld of the Carl Zeiss optical works in Jena, Germany, proposed a planetarium. Following his 1922 success with a 52-foot-diameter (16-meter) iron-rod dome built on the roof of the companys building the first lightweight steel structural framework in the world Bauersfeld consulted the structural engineers Dyckerhoff and Widmann about a larger version. Then, together with their designers Franz Dischinger and Ulrich Finsterwalder, he built the worlds first lightweight thin-shell concrete dome for Zeisss sister company, Schott and Partners. It was 131 feet (40 meters) in diameter and only 2.4 inches (6 centimeters) thick. The new structural technology, honed in later structures, made possible clear spans of lighter weight than had ever been imagined. Because concrete shells depend on configuration rather than mass for their strength, and because they exploit the fact that concrete is essentially a fluid, they have been characterized as the ultimate concrete form. Some of the most exciting examples have come from Spanish engineer-architects. Eduardo Torroja y Miret (1899 1961) was perhaps the most innovative engineer of the early twentieth century, notable for shell concrete roof designs that employed continuous surfaces and eliminated the need for ribs. Three examples should suffice. Torrojas first thin-shelled concrete roof was for the Market Hall in Algeciras, Spain (1933 1934), designed in conjunction with the architect Manuel Sanchez. The low-rise dome, supported at six points on its perimeter, spans 156 feet (48 meters); it is only 3.5 inches (9 centimeters) thick. In 1935, working with the architects Carlos Arniches Molt