economy of concrete structures begins in the design development stage with designers who have a good understanding of formwork logic. Often, two or more structural alternatives will meet the design objective equally well. However, one alternative may be significantly less expensive to build. Constructability, that is, making structural frames faster, simpler, and less costly to build, must begin in the earliest phase of the design effort. Economy in formwork begins with the design of a structure and continues through the selection of form materials, erection, stripping, care of forms between reuses, and reuse of forms, if any. When a building is designed, consideration should be given to each of the following methods of reducing the cost of formwork:
1. Prepare the structural and architectural designs simultaneously.
If this is done, the maximum possible economy in formwork can be ensured without sacrificing the structural and architectural needs of the building.
2. At the time a structure is designed, consider the materials and methods that will be required to make, erect, and remove the forms. A person or computer-aided drafting and design (CADD) operator can easily draw complicated surfaces, connections between structural members, and other details; however, making, erecting, and removing the formwork may be expensive.
3. If patented forms are to be used, design the structural members to comply with the standard dimensions of the forms that will be supplied by the particular form supplier who will furnish the forms for the job.
4. Use the same size of columns from the foundation to the roof, or, if this is impracticable, retain the same size for several floors. Adopting this practice will permit the use of beam and column forms without alteration.
5. Space columns uniformly throughout the building as much as possible or practicable. If this is not practicable, retaining the same position from floor to floor will result in economy.
6. Where possible, locate the columns so that the distances between adjacent faces will be multiples of 4 ft plus 1 in., to permit the unaltered use of 4-ft-wide sheets of plywood for slab decking.
7. Specify the same widths for columns and column-supported girders to reduce or eliminate the cutting and fitting of girder forms into column forms.
8. Specify beams of the same depth and spacing on each floor by choosing a depth that will permit the use of standard sizes of lumber, without ripping, for beam sides and bottoms, and for other structural members.
It is obvious that a concrete structure is designed to serve specific purposes, that is, to resist loads and deformations that will be applied to the structure, and to provide an appearance that is aesthetically pleasing. However, for such a structure, it frequently is possible to modify the design slightly to achieve economy without impairing the usability of the structure. The designer can integrate constructability into the project by allowing three basic concepts: design repetition, dimensional standards, and dimensional consistency.