Evaluation on properties of parallel-strand lumber

Parallel strand lumber (PSL) is a relatively new engineered wood product intended for a wide variety of structural applications. Using commercially available southern pine PSL and yellow-poplar PSL, this research was carried out to determine basic physical and mechanical properties of PSL, to examine variability in specific gravity, to develop a multiple regression model for predicting compressive strength, and to assess creep behavior under different conditions. The major findings and conclusions from this research are summarized as follows.; PSL has higher mean specific gravity than original solid wood, but shows lower variability in specific gravity. Southern pine PSL averages higher specific gravity than yellow-poplar PSL. PSL is much less hygroscopic and has lower equilibrium moisture content than original solid wood under the same environmental conditions. PSL exhibits directional nature in dimensional swelling with the largest swelling in the edgewise direction and the smallest in the longitudinal direction.; Bending stiffness and strength of PSL in edgewise direction are improved over original solid wood. Compressive strength of PSL in longitudinal direction is significantly greater than those in edgewise and flatwise directions. Longitudinal shear strength and internal bonding strength of southern pine PSL are comparable to those of yellow-poplar PSL. The degrees of linear correlation between mechanical properties and specific gravity depend upon a specific mechanical property, species, and direction.; Specific gravity is randomly distributed throughout the cross sectional area of a PSL billet. Variations due to wood species and random errors contribute most to the total variation in specific gravity of PSL, while variation between billets is relatively low in PSL.; A multiple linear regression relating transformed compressive strength to specific gravity, wood species, direction, and all their possible interactions meets model assumptions and can predict new data very well.; Under a constant temperature, creep deflection in PSL increases with the increase in relative humidity. Under a constant temperature and cyclic relative humidity levels, increase in creep deflection occurs during desorption and creep recovery takes place during adsorption. PSL shows greater creep deflection when exposed to the outdoor environment than to the indoor environment. Creep deflection in PSL increases with increasing load levels. In general, southern pine PSL shows better creep resistance than yellow-poplar PSL under various environmental conditions and load levels. Edgewise direction in PSL exhibits lower creep deflection than flatwise direction, due mainly to the former having higher bending stiffness than the latter. Four-element model can closely fit the observed creep behavior in PSL under a given constant condition.