The steps in the design of forms to support concrete slabs include the following:
1. Determine the total unit load on the floor decking, including the effect of impact, if any.
2. Select the type of floor decking, along with its net thickness.
3. Determine the safe spacing of floor joists, based on the strength or permissible deflection of the decking.
4. Select the floor joists, considering the load, type, size, and length of joists.
5. Select the type, size, and lengths of stringers, if required to support the joist.
6. Select the type, size, length, and safe spacing of shores, considering the load, the strength of the stringers, and the safe capacity of the shores.
Usually the most economical design of forms results when the joists are spaced for the maximum safe span of the decking.
Likewise, reasonably large joists, which permit long spans, thus requiring fewer stringers, will be economical in the cost of materials and in the cost of labor for erecting and removing the forms. The use of reasonably large stringers will permit the shores to be spaced greater distances apart, subject to the safe capacities of the shores, thus requiring fewer shores and reducing the labor cost of erecting and removing them.