Abstract: A tubular structural member, such as a horizontal box beam or vertical column, includes a set of elongated flange members of reinforced pultruded plastics material, and each flange member has longitudinally extending U-shaped opposite edge portions defining slots. Generally flat composite web members have opposite edge portions projecting into the slots, and epoxy adhesive rigidly secures the interfitting edge portions to form a tubular box-beam or multi-sided column. The web members may have curved or tapered opposite edge portions to form a beam with camber or a tapered column having a polygonal cross-sectional configuration. Reinforcing plates or ribs may be adhesively bonded to the flange and/or web members according to the structural loading on the member.