Response of Nailed Wood-Joist Floors to Static Loads

Forty-four laboratory-built wood-joist floors, divided into two groups with, respect to types of joists, subfloor, and finish floor, were tested and analyzed to establish their structural performance under concentrated loads and uniform loads. Tested floors were stronger and stiffer than predicted by the conventional beam analysis, which indicated that nailing subfloor to joists assures partial composite action between both connecting elements. Efficiency factors for T-beam analysis, evaluated for the test floors, offer better solution than the conventional beam analysis. A half inch plywood subfloor provided sufficient stiffness in a direction perpendicular to span to force the floor joists of various rigidities to deflect about equally when loaded with a uniform load. About two-thirds of a concentrated load, applied at a joist midspan, was distributed to six adjacent joists. Finish flooring nailed to the subfloor decreased the deflection, but had only negligible effect on the number of joists that deflected. Tests also showed that nailed floors built with Douglas-fir and western hemlock utility-grade (No. 3) joists and half-inch plywood subfloor were adequate for strength and deflection resistance.

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