totally new experience and many made it simply for the pleasure of watching the grandeur of the landscape. The journey, pulled by any of the twenty-six mountain locomotives in service, took a few minutes over two hours. The entire Vienna-Trieste line was opened at the end of July 1857.

The high elevation of the Semmering main tunnel caused problems because of freezing. Around the turn of the century, attempts were made to heat it with gas burners, and it was actually closed off with doors between trains. Flooding was also a difficulty, and after the particularly bad 1946–1947 winter, several hundred wagon loads of ice had to be excavated from the tunnel. A second tunnel was completed in March 1952 to overcome the difficulty. The Vienna-Gloggnitz line was electrified seven years later, and a four-year program was launched to upgrade tracks and buildings and electrify the Semmering section. The modifications were finished by May 1959. Coupled electric locomotives now transport up to 1,100 tons (1,000 tonnes) over the pass. Journey time, for either freight or passenger trains, is just forty-two minutes. Maximum speeds are limited to 37.5 mph (60 kph) on the north ramp and 44 mph (70 kph) on the south. The Semmering Railway continues to function well in the face of major technological change since it was first built, a testimony to the “detailed and well-founded planning” of von Ghega. However, the increased traffic has called for constant maintenance. The Semmering Railway, preserved in its nearly original form, has come under the Austrian Law of Protection of Monuments since 1923, a status confirmed by the Federal Office of Monuments as recently as March 1997. It was inscribed on UNESCO’s World Heritage List a year later.

Further reading

Niel, Alfred. 1960. Der Semmering and seine Bahn. Vienna: Ployer.

Winn, Bernard C. 1987. Railways Revisited: A Guide to Little-Known Railways in Austria and Germany. Merced: Incline Press.

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 company’s 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 world’s first lightweight thin-shell concrete dome for Zeiss’s 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. Torroja’s 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 Moltó and Martín Domínguez Esteban, Torroja produced the folded plate roof for the grandstand at the Hipódromo de la Zarzuela, Madrid. The cantilever on the graceful structure is 73 feet (22 meters). In the same year, with architect Secundino Zuazo, he designed a 180-foot-long (55-meter) vaulted roof over an indoor pelota court in Madrid. Its two intersecting parallel vaults, of 40 and 21 feet (12.2 and 6.4 meters) radius, respectively, span a total of 98 feet (30 meters); the general thickness of the vast shell is a mere 3.14 inches (8 centimeters). With José Maria Aguirre, in 1934 Torroja founded the Instituto Técnico de la Construcción y Edificación in Madrid to “develop new uses and theories for reinforced concrete”; after his death in 1961,