外文翻譯---抗側(cè)向荷載的結(jié)構(gòu)體系-資料下載頁
2025-08-22 17:10本頁面
【正文】 space frame. Indeed, the system is used often wherein the shear stiffness of the outer tube is zero. The United States Steel Building, Pittsburgh, illustrates the system very well. Here, the inner tube is a braced frame, the outer tube has no shear stiffness, and the two systems are coupled if they were considered as systems passing in a straight line from the “hat” structure. Note that the exterior columns would be improperly modeled if they were considered as systems passing in a straight line from the “hat” to the foundations。 these columns are perhaps 15% stiffer as they follow the inner columns change from tension to pression over the height of the tube, with the inflection point at about 5/8 of the height of the tube. The outer columns, of course, carry the same axial force under lateral load for the full height of the columns because the columns because the shear stiffness of the system is close to zoo.The space structures of outrigger girders or trusses, that connect the inner tube to the outer tube, are located often at several levels in the building. The ATamp。T headquarters is an example of an astonishing array of interactive elements:The structural system is 94 ft () wide, 196ft() long, and 601ft() high.Two inner tubes are provided, each 32ft() by 40 ft() centered 90 ft() apart in the long direction of the building.The inner tubes are braced in the short direction, but with zero shear stiffness in the long direction.A single outer tube is supplied, which encircles the building perimeter.The outer tube is a momentresisting frame, but with zero shear stiffness for the center50ft () of each of the long sides.A spacetruss hat structure is provided at the top of the building.A similar space truss is located near the bottom of the building.The entire assembly is laterally supported at the base on twin steelplate tubes, because the shear stiffness of the outer tube goes to zero at the base of the building.Cellular structuresA classic example of a cellular structure is the Sears Tower, Chicago, a bundled tube structure of nine separate tubes. While the Sears Tower contains nine nearly identical tubes, the basic structural system has special application for buildings of irregular shape, as the several tubes need not be similar in plan shape, It is not unmon that some of the individual tubes one of the strengths and one of the weaknesses of the system.This special weakness of this system, particularly in framed tubes, has to do with the concept of differential column shortening. The shortening of a column under load is given by the expression For building of 12ft() floortofloor distances and an average pressive stress of 15ksi(138MPa), the shortening of a column under load is 15(12)(12)/29,000 or ()per story. At 50 stories, the column will have shortened to in. (94mm) less than its unstressed length. Where one cell of a bundled tube system is, say, 50stories high and an adjacent cell is, say, 100stories high, those columns near the boundary between, the two systems need to have this differential deflection reconciled.Major structural work has been found to be needed at such locations. In at least one building, the Rialto Project., Melbourne, the structural engineer found it necessary to vertically prestress the lower height columns so as to reconcile the differential deflections of columns in close proximity with the posttensioning of the shorter column simulating the weight to be added on to adjacent, higher columns.
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