(Received 21 July 1997; accepted 8 May 1998)
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A total of 19 440 virtual structural floors of a geometry and material configuration consistent with those used in commercial construction (commercial floors) throughout North America was numerically analyzed to determine deflection characteristics under a constant uniformly distributed load of 95 lbf/ft2 (4.55 kPa). The intent of these analyses was to determine the effect of joist variability on the deflection behavior of floors with and without elastomeric construction adhesive (ECA) between sheathing and joists. The joist property (modulus of elasticity, MOE) was allowed to vary in a systematic fashion between 1250 (8.62) and 3250 (22.4) ksi (MPa) in increments of 250 ksi (1.72 MPa). In addition, the variability of the joists (at each value of MOE) varied between coefficient of variation (COV) values of 0.025 to 0.150 in increments of 0.025. One hundred eighty floors were evaluated with and without ECAs at each mean MOE value and at each COV value for the joists. All other sheathing and connector properties remained constant.
The results indicated that the contribution of the ECA to reducing floor deflection under uniformly distributed loads was dependent in large part on the mean stiffness of the floor joists and to a much lesser extent on the COV of the joists. For joists of lower stiffness, the contribution of ECA had a more pronounced effect on mitigating the floor deflection level. Reductions of nearly 10% were realized when the mean joist MOE was 1250 ksi. For floors made with stiffer joists (mean MOE 4 3250 ksi), floor deflections were reduced by only about 5.5% when adhesive was used. The presence of ECA between joist and sheathing did not have much effect on reducing the variability of floor deflection behavior.
Professor of wood engineering, Colorado State University, Fort Collins, CO
Structural engineer, Charles Robinson, P.E., Inc., Fort Collins, CO
Stock #: JTE12119J