Wood Joist Floors: Effects of Joist Variability on Floor Stiffness

Abstract : A theoretical study was conducted of the performance (deflection) of wood-joist floors subjected to distributed loads. Eleven 'benchmark' floors, typical of current construction practice, were analyzed. Results demonstrated that composite action, ignored by current design methods, can be substantial. Performance distributions were calculated for five floors from available joist stiffness data. Results showed that even when the joist stiffnesses are below design values, composite action reduces deflections to less than allowable design levels. The effects of joist variability on floor performance variations were studied by assuming distributions of joist stiffness, and calculating corresponding distributions of floor performance. Results demonstrate how joist variability is reduced when the joists are assembled into complete floor systems. The results of these analyses provide valuable data on the current performance levels of wood-joist floor systems, and the methodologies developed will be of benefit to future efforts in this area. (Author)