STEEL

   Steel, an alloy of iron and trace amounts of carbon, is a stronger material than cast iron. Known since antiquity, steel began to be produced with some degree of efficiency only in the mid-19th century, with a new industrial procedure called the Bessemer process. The first structural use of steel in architecture is found in William Le Baron Jenney's early skyscrapers built in Chicago, and one of the most famous early steel skeletal structures is the Fuller Building in New York City, better known as the Flatiron Building. Constructed in 1902 by Daniel Burnham, this Beaux-Arts style, 285-foot-tall skyscraper was constructed in a triangular shape to accommodate the area where Fifth Avenue and Broadway intersect at an angle. Steel was stronger, lighter, and less expensive than cast iron; its introduction as the skeleton frame of large-scale buildings altered the course of architectural history.

   Steel constructions often featured technically challenging designs as well. Steel was also used for suspension bridges, as exemplified in the Brooklyn Bridge, constructed by John Augustus Roebling and his son Washington Augustus Roebling in the 1860s-1880s. John Roebling had invented twisted wire cabling to replace the chains previously used in bridge suspensions, and when completed, the Brooklyn Bridge in New York City was the longest in the world. Heavy steel cables hang from two massive stone towers that feature paired pointed arches flanked by pilasters. R. Buckminster Fuller, an early technical architect, also used steel for his geodesic dome constructed for the United States Pavilion at Expo '67 in Montreal. In many ways, Fuller's dome anticipated the focus placed on the highly technical architectural style introduced in the 1980s and called High-Tech architecture. These buildings were increasingly constructed from a stainless steel exoskeleton that more effectively resists corrosion, and architects were increasingly exploring the use of titanium, such as Frank Gehry in his Post-Modern buildings. His Guggenheim Museum in Bilbao, Spain, from the 1990s, is completely covered with Grade 1 titanium that features a slight rippling effect to create a softer texture to the exterior. Despite the introduction of these new materials, steel continues to be structurally superior and therefore central to technically sophisticated design and construction.