Economical formwork is often the decisive factor in the final cost of cast-in-place reinforced concrete high rise structures. Formwork frequently costs more than the concrete used, and sometimes more than the concrete and reinforcing steel combined. Unlike concrete and reinforcing steel, the costs of which are relatively constant, formwork design offers opportunities for major savings in time, materials, labor, and equipment. In addition to these direct cost reductions, economies can be achieved in other trades affecting and affected by formwork. The most effective approach to cost reduction start with well-established, standardized form sizes and lumber and plywood dimensions. Non-conforming dimensions are expensive, and avoiding variations pays dividends by eliminating special form sizes, costly alterations, and waste of material. Thus, the two basic rules of formwork design are: (1) standard form sizes and materials, and (2) maximum reuse of the forms. Here are some specific ways to achieve these goals: (1) do not try to save concrete and steel by meticulously calculating every beam and column to fit the load and span exactly. You may save pennies on concrete and steel while you waste dollars on formwork materials and labor. (2) Select beam and column sizes for maximum conditions, and then use the same sizes repeatedly. (3) Keep beams and columns simple. (4) Keep beams, slabs and joist soffits at a constant uniform height for as many floors as possible. (5) Where column size must be changed, reduce one dimension at a time and retain for as many floors as possible. And (6) design span and load combinations for uniform depth construction wherever possible.
