Three simple tools are used to both preform and mold a composite layup into a J-beam. A first composite charge is preformed into a C-channel using a first tool, and a second composite charge is formed into a Z-channel using both the first tool and a second tool. The C-channel and Z-channel are laid up between the first and second tools, following which a perform composite cap and third tool are added to complete the layup and the tool assembly. The layup may be molded using vacuum bagging techniques and subsequently cured while held in the tool assembly.