Since formwork generally is a temporary installation (and not part of the building or other finished product with which the specifier is concerned), it may be that little attention is given to the formwork specification even though it has a vital bearing on cost and quality of the concrete. The dollar value of good formwork specifications takes on particular meaning when we remember that 35 to 60 percent of a concrete structure's cost may be in formwork. From the point of view of the owner, shortcutting these specifications is false economy.
Areas discussed in this article include: the need for flexibility; checklist of information needed by the form builder; stripping time and reshoring provisions; camber; shell structures; structures designed for composite action; tolerances; architectural concrete; and maintaining the state of the art.
Construction of shells, domes and folded plates presents some unique forming problems. Because of the relatively thin section of the shell, imperfections in the forms are larger in comparison with the total depth of the finished member than in beams and slabs. The curved and inclined surfaces and the resulting stress patterns also present difficulties not ordinarily encountered in forming rectilinear structures. Since the weight of the supporting falsework may, in many cases, be equal to or greater than the design live load of the shell, the form must be designed so that it will not bind or hang up and overload the structure during decentering. The forms must not become keyed into the concrete in any way that would hinder stripping or transfer the load of the falsework to the shell.