Very tall multistoried building. The term originally applied to buildings of 10–20 stories, but now generally describes high-rises of more than 40–50 stories. James Bogardus (1800–1874) built the pioneering Cast Iron Building, New York (1848), with a rigid iron frame providing the main support for upper-floor and roof loads. The refinement of the Bessemer process for making steel (lighter and stronger than iron) made extremely tall buildings possible. Chicago's Home Insurance Co. Building (1884–85), by William Le Baron Jenney (1832–1907), was the first tall building to use a steel skeleton. Structurally, skyscrapers consist of a substructure supported by a deep foundation of piles or caissons beneath the ground, an aboveground superstructure of columns and girders, and a curtain wall hung on the structural framework. Tube structures, braced tubes, and trussed tubes were developed to give skyscrapers the ability to resist lateral wind and seismic forces. The bundled-tube system, developed by Fazlur Khan (1928–1982), uses narrow steel tubes clustered together to form exceptionally rigid columns, and has been used to build some of the world's tallest skyscrapers (e.g., Sears Tower). Skyscraper design and decoration have passed through several stages: Louis Sullivan emphasized verticality; the firm of McKim, Mead, & White (seeCharles F. McKim, Stanford White) stressed Neoclassicism. The International Style was ideally suited to skyscraper design. Originally a form of commercial architecture, skyscrapers have increasingly been used for residential purposes as well. See alsosetback.