Preliminary factors to be considered in the selection of a sitecast concrete framing system for a building include the following (Figures 14.43 and 14.44):
1. Are the bays of the building square or nearly square? If so, a two-way system will probably be more economical than a one-way system.
2. How long are the spans? Spans up to 25 or 30 feet (7.6 or 9.1 m) are usually accomplished most economically with a two-way flat plate or flat slab system because of the relative simplicity of the formwork. For longer spans, a one-way joist system may be a good choice. Posttensioning extends significantly the economical span range of any of these systems.
3. How heavy are the loads? Heavy industrial loadings are borne better by thicker slabs and larger beams than they are by light joist construction. Ordinary commercial, institutional, and residential loadings are carried easily by flat plate or joist systems.
4. Will there be a finish ceiling beneath the slab? If not, flat plate and one-way slab construction have smooth, paintable undersides that can serve as ceilings.
5. Does the lateral stability of the building against wind and seismic loads have to be provided by the rigidity of the concrete frame? Flat plate floors may not be sufficiently rigid for this purpose, which would favor a one-way system with its deeper beam-to-column connections.
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