Table 1. Single Joint Sample Results Listed
by Type of Joint
Table 1. Single Joint Sample Results Listed by Type of Joint
Subjective observation indicates that the larger the piece of wood from the adjacent surface, the higher the loads resisted by the joint. While intuitively obvious, the relationship generally has been tested only in casual ways, e.g. examining the damaged timbers after the cathedral roof collapses.
The three tenoned samples failed differently. The particle board tenons snapped before they could induce splitting in the long grain of the wood. While there was minor failure in their glue surfaces, the majority of failure was in the tenon itself after which the joint rotated open with very little wood pulled away from the adjacent surfaces.
Four-Joint Sample Group The three samples in the four-joint group failed at forces ranging from 12,800 to 18,600 newtons at displacements from 3 to 4 mm. The tenon joint achieved the highest load rating. The biscuit joint which had surfaces dampened with water held the second highest load (16,600 N). The 3-biscuit joint made with urethane applied to dry wood failed at the lowest (but still strong) load. (Figure 7)
Four Joint Specimens Bonded
with Urethane
Figure 7. Four-Joint Sample Group - Load
vrs. Deformation
Figure 7. Four-Joint Sample Group - Load vrs. Deformation
The mean maximum loads of the two four-sided biscuit samples equals 3.9 times the mean maximum loads of the similarly constructed single-joint samples (#9,10 and 11 from Figure 6). A four joint frame has the strength of four joints.
