Farm (structure)


August 8, 2022

Firm (fr. ferme, from lat. firmus — "strong", "strong") is a geometrically unchanged holding structure consisting of rectilinear rods, the nodal connections of which are considered hinged in the calculations. Rods in nodal trusses are rigidly connected: by welding, bolts, rivets, shapes, or in general, the entire truss is made into a monolithic structure. Despite this, experiments show that bending moments in rectilinear rods are negligible compared to longitudinal forces. Therefore, in practical calculations, the values ​​of bending moments are neglected, and for the construction of the calculation scheme of the truss, it is assumed that ideal cylindrical hinges are installed in the nodes.

Assignment of Farms

Farms are used mainly in construction (covering of industrial and civil buildings, hangars, railway stations, markets, sports facilities, thrust elements of railway and road bridges, towers, cranes, oil towers, supports of high-voltage network lines, hydraulic gates, etc.), as well as as holding structures of machines and mechanisms. According to the type of material, trusses are metal, reinforced concrete, wooden and combined. When trusses are used as a structural support system, such structural solutions are chosen that provide for load transfer only at truss nodes in order to avoid rod deflections. Then only longitudinal tension-compression forces arise in the truss rods. The lack of bending of the rods allows you to choose smaller sizes of their cross-section compared to rods working on bending. Thanks to this, material consumption in trusses is lower than in beams, they are lighter in weight, but the labor intensity of their manufacture is greater.

Truss structures

The connection points of the truss rods are called nodes. Rods located along the contour at the top and bottom of the truss form the upper and lower belts, respectively, and the rods located between the truss belts form a lattice. The lattice consists of inclined rods - braces and vertical - risers. Stretched risers are sometimes called hangers. Risers and braces located near the supports are called supporting. The horizontal projection of the distance between the supports of the truss is called a span. Horizontal projection of the distance between adjacent upper or lower nodes