Method of manufacturing concrete beams

A method of simultaneously manufacturing a plurality of concrete beams having upper and lower flange parts which are separated by a web part and which extend over a whole length of said beams, said web part being provided with a plurality of recesses having thin concrete membranes disposed therein, comprising the steps of:

• providing a first undivided form part constituting a bottom part including a plurality of elongate, mutually spaced, recesses, said recesses having a shape corresponding to an outer portion of said upper flange part of said beams;
• providing a plurality of second form parts constituting a plurality of elongate intermediate members having a plurality of projections extending from opposing sides thereof;
• placing said intermediate members on said bottom part between said recesses therein such that lines of contact between said intermediate members and said bottom part are displaced from the bottoms of said recesses and no dividing planes are located along the upper flange part forming portions of said first form part, said members together with said bottom part forming an upwardly open mold chamber in which each beam is to be formed and said plurality of projections extending from opposing sides of said elongate intermediate members confronting projections of adjacent elongate intermediate members providing a small gap therebetween;
• filling said chambers with concrete such that said concrete fills said chamber including said gap to form said concrete beams with membranes in such a manner that flash is not formed on said outer portion of said upper flange part of said beams formed by said first form part;
• allowing said concrete to harden;
• and
• removing said intermediate members with said beams from said bottom part and removing said beams from said intermediate members.