【文章內(nèi)容簡(jiǎn)介】 ure. Resistance to wind forces in the Crystal palace was provided by diagonal iron rods. Two feature are particularly important in the history of metal construction。 first, the use of latticed girder, which are small trusses, a form first developed in timber bridges and other structures and translated into metal by Paxton 。 and second, the joining of wroughtiron tension members and castiron pression members by means of rivets inserted while hot. In 1853 the first metal floor beams were rolled for the Cooper Union Building in New York. In the light of the principal market demand for iron beams at the time, it is not surprising that the Cooper Union beams closely resembled railroad rails. The development of the Bessemer and SiemensMartin processes in the 1850s and 1860s suddenly open the way to the use of steel for structural purpose. Stronger than iron in both tension and pression ,the newly available metal was seized on by imaginative engineers, notably by those involved in building the great number of heavy railroad bridges then in demand in Britain, Europe, and the . A notable example was the Eads Bridge, also known as the St. Louis Bridge, in St. Louis (18671874), in which tubular steel ribs were used to form arches with a span of more than 500ft (). In Britain, the Firth of Forth cantilever bridge (188390) employed tubular struts, some 12 ft () in diameter and 350 ft (107m) long. Such bridges and other structures were important in leading to the development and enforcement of standards and codification of permissible design stresses. The lack of adequate theoretical knowledge, and even of an adequate basis for theoretical studies, limited the value of stress analysis during the early years of the 20th century,as iccasionally failures,such as that of a cantilever bridge in Quebec in 1907, failures were rare in the metalskeleton office buildings。the simplicity of their design proved highly practical even in the absence of sophisticated analysis techniques. Throughout the first third of the century, ordinary carbon steel, without any special alloy strengthening or hardening, was universally used. The possibilities inherent in metal construction for highrise building was demonstrated to the world by the Paris Exposition of which AlexandreGustave Eiffel, a leading French bridge engineer, erected an openwork metal tower 300m (984 ft) high. Not only was the heightmore than double that of the Great Pyramidremarkable, but the speed of erection and low cost were even more so, a small crew pleted the work in a few months. The first skyscrapers. Meantime, in the United States another important development was taking place. In 188485 Maj. William Le Baron Jenney, a Chicago engineer , had designed the Home Insurance Building, ten stories high, with a metal skeleton. Jenney’s beams were of Bessemer steel, though his columns were cast iron. Cast iron lintels supporting masonry over window openings were, in turn, supported on the cast iron columns. Soild masonry court and party walls provided lateral support against wind loading. Within a decade the same type of construction had been used in more than 30 office buildings in Chicago and New York. Steel played a larger and larger role in these , with riveted connections for beams and columns, sometimes strengthened for wind bracing by overlaying gusset plates at the junction of vertical and horizontal members. Light masonry curtain walls, supported at each floor level, replaced the old heavy masonry curtain walls, supported at each floor level , replaced the old heavy masonry. Though the new construction form was to remain centred almost entirely in America for several decade, its impact on the steel industry was worldwide. By the last years of the 19th century, the basic structural shapesI beams up to 20 in. ( ) in depth and Z and T shapes of lesser proportions were readily available, to bine with plates of several widths and thicknesses to make efficient members of any required size and strength. In 1885 the heaviest structural shape produced through hotrolling weighed less than 100 pounds (45 kilograms) per foot。 decade by decade this figure rose until in the 1960s it exceeded 700 pounds (320 kilograms) per foot. Coincident with the introduction of structural steel came the introduction of the Otis elec