Self-supporting girder structure

In combination with self-supporting linear girder structure made up of a plurality of identical, triangular, separable sections of molded plastic arranged linearly, each section having an equilateral triangular cross section transverse to said linear structure, the adjoining faces of said sections having complementary interengaging projections and recesses to prevent relative transverse movement, longitudinal openings through each section adjacent the apices of the triangular section, a metal tubular bush through each opening, so that said bushes when assembled form longitudinal passages through said girder structure, the bushes in each section being equally spaced at the apices of the triangular section and having the exact length of a section with their ends flush with the end faces of the sections, longitudinal tensioning members extending through said passages from end to end, and clamping means on the ends of said tensioning members to clamp said sections together, said clamping means placing said longitudinal members under tension and prestressing said sections, said bushes engaging to limit compression of said sections, and a pair of triangular members each having the cross section of an equilateral triangle secured to the top apices of certain sections so that one face of each of two triangular members abuts opposite faces at the top of a section to form a flat support composed of two faces of the triangular members and a conveyor supported by said structure on said two faces which form a plane parallel to the section face opposite to the top of the section.