土木工程专业英语课件作者陈瑛1.1ClassificationandBehaviorofStructuralSystemsandElements.pptVIP

1.1 Classification and Behavior of Structural Systems and Elements Primary Structural Elements (Based on Stiffness) Rigid element – beam, column or strut, arch, flat plate, singly-curved plate, and shell Flexible elements – cable (straight or draped) and membrane Derived elements – frame, truss, geodesic dome, net Frames The frame has rigid joints that are made between vertical and horizontal members. This joint rigidity imparts (给予) a measure of stability against lateral forces. In a framed system both beams and columns are bent or bowed（弯如弓的）as a consequence of the action of the load on the structure. Trusses 桁架 Trusses are structural members made by assembling short, straight members into triangulated patterns. The resultant （组合的, 合成的）structure is rigid as a result of the exact （精确的) way the individual line elements are positioned relative to one another. Trusses 桁架 Some patterns (e.g. a pattern of squares rather than triangles) do not necessarily yield a structure that is rigid (unless joints are treated in the same way as in framed structures). Arches An arch is a curved, line-forming structural member that spans between two points. block arch (块拱） rigid arch （刚性拱） fixed two-hinged, three-hinged Block arch(块拱） The common image of an arch is that of a structure composed of separate wedge-shaped pieces that retain their position by mutual pressure induced by the load . mutual [5mju:tFuEl] adj. 相互的, 共有的 The exact shape of the curve and the nature of the loading are critical determinants as to whether the resultant assembly is stable. When shapes are formed by simply stacking rigid block elements, the resultant structure is functional and stable only when the action of the load is to induce in-plane forces that cause the structure to compress uniformly. Structures of this type cannot carry loads that induce elongations or any pronounced type of bowing in the member (the blocks simply pull apart and failure occurs). The strength of a block structur