【正文】 in tube. Another system in reinforced concrete for office buildings bines the traditional shear wall construction with an exterior framed tube. The system consists of an outer framed tube of very closely spaced columns and an interior rigid shear wall tube enclosing the central service area. The system (Fig .2), known as the tubeintube system , made it possible to design the world’s present tallest (714ft or 218m)lightweight concrete building ( the 52story One Shell Plaza Building in Houston) for the unit price of a traditional shear wall structure of only 35 stories. Systems bining both concrete and steel have also been developed, an examle of which is the posite system developed by skidmore, Owings amp。Merril in which an exterior closely spaced framed tube in concrete envelops an interior steel framing, thereby bining the advantages of both reinforced concrete and structural steel systems. The 52story One Shell Square Building in New Orleans is based on this system. Steel construction refers to a broad range of building construction in which steel plays the leading role. Most steel construction consists of largescale buildings or engineering works, with the steel generally in the form of beams, girders, bars, plates, and other members shaped through the hotrolled process. Despite the increased use of other materials, steel construction remained a major outlet for the steel industries of the , , , Japan, West German, France, and other steel producers in the 1970s. Early history. The history of steel construction begins paradoxically several decades before the introduction of the Bessemer and the SiemensMartin (openjhearth) processes made it possible to produce steel in quantities sufficient for structure use. Many of problems of steel construction were studied earlier in connection with iron construction, which began with the Coalbrookdale Bridge, built in cast iron over the Severn River in England in 1777. This and subsequent iron bridge work, in addition to the construction of steam boilers and iron ship hulls , spurred the development of techniques for fabricating, designing, and jioning. The advantages of iron over masonry lay in the much smaller amounts of material required. The truss form, based on the resistance of the triangle to deformation, long used in timber, was translated effectively into iron, with cast iron being used for pression , those bearing the weight of direct loadingand wrought iron being used for tension , those bearing the pull of suspended loading. The technique for passing iron, heated to the plastic state, between rolls to form flat and rounded bars, was developed as early as 1800。 and in 1849 the first I beams, feet () long , were fabricated as roof girders for a Paris railroad station. Two years later Joseph Paxton of England built the Crystal Palace for the London Exposition of 1851. He is said to have conceived the idea of cage constructionusing relatively slender iron beams as a skeleton for the glass walls of a large, open structure. 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。 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 di