Bending Performance of Composite Wood I-Joist/Oriented Strand Board Panel Assemblies

This study examined the bending performance of composite I-joist/oriented strand board (OSB) structural roof panels. The 1.22-m-wide panels were fabricated from commercially available I-joists with OSB sheathing bonded to the top and bottom I-joist flanges. To provide baseline bending performance, two sets of 10 bare I-joists were tested to failure in four-point quasistatic bending. The first consisted of 4.72-m-span, 241-mm-deep joists, and the second set consisted of 7.16-m-span, 356-mm-deep joists. Two sets of 10 I-joist/OSB panels fabricated with identical I-joists of the same spans were tested in four-point bending. Results of the bend tests showed strength gains of 59 to 124 percent and stiffness gains of 79 to 115 percent on a per-joist basis for the I-joist/OSB panels. While the bare I-joists primarily exhibited bending failures, the panels predominantly failed in shear. These strength and stiffness gains and the shift in failure mode indicate that the bonded OSB sheathing significantly improved panel bending strength. A transformed section analysis predicted panel stiffness reasonably well and indicated that shear failure was the most likely panel failure mode. Finally, four specimens were tested under sustained loading equal to 55 percent of the 5 percent parametric lower tolerance limit. Two of the specimens tested under sustained loading failed in creep rupture. Results of this study indicate that the roof panels show promise for practical application as long-span, pre-insulated structural members. However, creep deformation and creep rupture need further study, as does the durability of the I-joist–OSB bond line.