Relationship between Tooth Withdrawal Strength and Specific Gravity for Metal Plate Truss Connections

The objectives of this research were twofold: a) to define the relationship between tooth withdrawal and specific gravity for southern pine lumber and four different plate-to-wood load orientations, and b) to demonstrate how these relationships could be applied to new lumber grades to predict tooth withdrawal performance so that additional testing would not be necessary. The four orientations investigated were: a.) LRAA - plate axis parallel to load and wood grain parallel to load. b.) LREA - plate axis perpendicular to load and wood grain parallel to load. c.) LRAE - plate axis parallel to load and wood grain perpendicular to load. d.) LREE - plate axis perpendicular to load and wood grain perpendicular to load. For the LRAA, LREA, LRAE, LREE orientations, the following sample sizes were respectively: 27, 22, 27, and 29. Results showed specific gravity and embedment gap were excellent predictors of ultimate tooth withdrawal stress for the LRAA orientation. However, neither specific gravity nor percentage of latewood significantly influenced the location of tooth withdrawal. For the LREA orientation, specific gravity alone was a good predictor of ultimate tooth withdrawal stress. Furthermore, the side of the joint test specimen where tooth withdrawal initiated was dependent on the wood piece with the lowest mean specific gravity. For the LRAE orientation, specific gravity was a marginal predictor of ultimate tooth withdrawal stress. For the LREE orientation, specific gravity was a decent predictor of ultimate tooth-withdrawal stress.