EXPERIMENTAL INVESTIGATION ON TRUSSES MADE OF GLULAM AND BIRCH PLYWOOD GUSSET PLATES

This paper investigates the load-carrying capacity of trusses consisting of glulam elements joined through birch plywood plates by means of either adhesively gluing or mechanical fasteners. A total of 6 trusses with a span of 7 meters were tested, three trusses for each connection type. Furthermore, the thickness of the plywood plates varied between 9 and 21 millimetres (mm). The main purpose of this research was to gain a better understanding of the failure mode of birch plywood subjected to a multi-axial stress state with loads from multiple directions. Therefore, the truss specimens were designed so that failure occurred in the central plywood plate, which was subjected to a multi-axial stress state. All specimens with mechanical connectors, as well as the bonded specimen with the thinnest plywood plate (9 mm), failed in the plywood plates. In contrast, bonded specimens with 12 and 21 mm thick plywood failed at the bonded interface between plywood and glulam. For specimens that failed in the plywood plates, the experimental results showed an increase in load-carrying capacity with increasing plywood plate thickness. Furthermore, glued specimens generally exhibited higher load-carrying capacity and elastic stiffness than those with mechanical connectors. For both glued and mechanically connected specimens, the thickness of the plywood plate did not show a significant influence on the stiffness. The analytical load-carrying capacity estimations slightly overestimated the experimental results of specimens that showed plywood failure, but they generally showed good agreement. The overestimation was attributed to the size effect of birch plywood's mechanical properties.