Need a steel beam? You can 3D print PLA beams that are as strong as a steel beam of equivalent weight according to [RepRap]. The Python code for FreeCAD generates a repeating structure especially well suited for belt printers that can print a beam of any length. Keep in mind, of course, given two things that weigh the same, if one is made of steel and the other PLA, the steel one will be physically smaller.
The beams are repeating tetrahedrons which are quite strong with a lot of material on the outer faces to resist bending. Each beam end has a neat block with a wiring hole and a ring of small holes that allow you to mount the beams to things or each other with 30 degree increments of rotation.