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truss,in architecture and engineering, a supporting structure or framework composed of beams, girders, or rods commonly of steel or wood lying in a single plane. A truss usually takes the form of a triangle or combination of triangles, since this design ensures the greatest rigidity. Trusses are used for large spans and heavy loads, especially in bridges and roofs. Their open construction is lighter than, yet just as strong as, a beam with a solid web between upper and lower lines. The members are known as tie-beams, posts, rafters, and struts; the distance over which the truss extends is called the span. The upper and lower lines or beams are connected by web members.
suspended arch truss
a load-bearing structural system consisting of straight bars, the assembly joints of which are considered to be hinged for purposes of structural analysis of the design. Trusses are used primarily in construction—for the roofs of buildings, bridge spans, masts, supports for power transmission lines and gates in hydraulic engineering structures—and as load-bearing structural members in machines and mechanisms. They may be constructed from metal, reinforced concrete, wood, or combinations of materials, such as metal and wood. The material chosen and the design of the truss depend on the purpose of the building or structure, the type of roof, and method used to support the truss, and other factors.
Although they are considered to be hinged, the joints of trusses in practice have some degree of rigidity. In the design of trusses, provision is usually made for the application of external loads to the joints; for example, the stringers of a roof rest on a truss at the joints of the upper chord, and the beams of overhead cranes are secured to the joints of the lower chord of a truss. The assumptions of hinged connection of joints and the application of loads at the joints make it possible during the computation of stress to consider only the axial longitudinal forces in the bars; in this case, equally distributed stresses occur in the transverse sections of the bars, which makes it possible to make the most efficient use of the material. The forces in the bars of statically determinate, single-plane trusses are determined from the equations of statics; for three-dimensional trusses they are usually determined by converting the structure into a system of single-plane trusses. Statically indeterminate trusses are analyzed by means of the equations of the force method (seeSTRUCTURAL MECHANICS), in which the coefficients for the unknown quantities (displacements) are determined by considering only the effect of normal forces in elements of the truss. Live loads are computed from the tributary areas for loads.
L. V. KASAB’IAN