Abstract: The structures of the present invention start with a basic hollow tube of any desired outer shape and made of paper, plastic or metal. When paper is used, it is vacuum impregnated with a plastic resin and oven baked to give it rigidity. The tube may also be covered with an ornamental veneer, if desired. The tubes are provided with suitable openings to receive matching counterparts fitting against the openings. Strong, rigid core members of wood, plastic or metal are positioned in the tubular members with the abutting portions of the core members interconnected. The structure is placed in a clamp to hold the parts together in proper position. Polyurethane is then poured into one end, the end is capped, and the structure is rotated to evenly distribute the polyurethane. The urethane sets at room temperature and expands as it sets to internally mold the members into a solid structure. The finished structure can be drilled, machined, or bolted to add features in the conventional manner.