A lattice-form support beam with triangular cross-section, including: - a set of three side rails (2, 3, 4) extending parallel along a main direction of extension of the beam, - a plurality of triangular assemblies distributed along the main extension direction and each extending in a plane perpendicular to said main direction of extension, each triangular assembly being formed by three cross-beams (5, 6, 7) mechanically connecting the side rails in pairs, - a plurality of tie rods (9, 9a, 9b, 9c, 9d) each mechanically connecting the side rails (2, 3, 4) in pairs, extending between two consecutive triangular assemblies, - a plurality of fastening plates (8a, 8b, 8c) fastened to the side rails, each fastening plate (8a, 8b, 8c) fastened to a given side rail among the three side rails including a first flat flange and a second flat flange extending radially with respect to said given side rail, the first flat flange forming a first fastening surface for removable fastening one end of a first cross-beam among said plurality of cross-beams, one end of a first tie rod and one end of a second tie rod among said plurality of tie rods, and the second flat flange forming a second fastening surface for the removable fastening of a second cross-beam among said plurality of cross-beams, of an end of a third tie rod and of an end of a fourth tie rod among said plurality of tie rods, each fastening plate (8a, 8b, 8c) comprising a central surface matching the external shape of said given side rail and being rigidly attached to said given side rail, said first flat flange and said second flat flange extending laterally from the central surface and extending radially with respect to the given side rail, characterized in that the end of the first cross-beam, the end of the first tie rod and the end of the second tie rod are fastened together by a single first bolting system including a fastening screw crossing through the same fastening hole of the first flat flange, in that the end of the second cross-beam, the end of the third tie rod and the end of the fourth tie rod are fastened together by a single second bolting system including a fastening screw crossing through the same fastening hole of the second flat flange, in that the end of the first cross-beam is fastened to an inner face of the first flat flange while the end of the first tie rod and the end of the second tie rod are fastened to an outer face of the first flat flange, and in that the end of the second cross-beam is fastened to an inner face of the second flat flange while the end of the third tie rod and the end of the fourth tie rod are fastened to an outer face of the second flat flange. - a set of three side rails (2, 3, 4) extending parallel along a main direction of extension of the beam, - a plurality of triangular assemblies distributed along the main extension direction and each extending in a plane perpendicular to said main direction of extension, each triangular assembly being formed by three cross-beams (5, 6, 7) mechanically connecting the side rails in pairs, - a plurality of tie rods (9, 9a, 9b, 9c, 9d) each mechanically connecting the side rails (2, 3, 4) in pairs, extending between two consecutive triangular assemblies, - a plurality of fastening plates (8a, 8b, 8c) fastened to the side rails, each fastening plate (8a, 8b, 8c) fastened to a given side rail among the three side rails including a first flat flange and a second flat flange extending radially with respect to said given side rail, the first flat flange forming a first fastening surface for removable fastening one end of a first cross-beam among said plurality of cross-beams, one end of a first tie rod and one end of a second tie rod among said plurality of tie rods, and the second flat flange forming a second fastening surface for the removable fastening of a second cross-beam among said plurality of cross-beams, of an end of a third tie rod and of an end of a fourth tie rod among said plurality of tie rods, each fastening plate (8a, 8b, 8c) comprising a central surface matching the external shape of said given side rail and being rigidly attached to said given side rail, said first flat flange and said second flat flange extending laterally from the central surface and extending radially with respect to the given side rail,