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

The objectives of this research were to 1) define the relationship between tooth withdrawal strength and specific gravity (SG) for southern pine lumber and four different plate-to-wood load orientations ; and 2) 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 : 1) LRAA : plate axis parallel to load and wood grain parallel to load ; 2) LREA : plate axis perpendicular to load and wood grain parallel to load ; 3) LRAE : plate axis parallel to load and wood grain perpendicular to load ; and 4) LREE : plate axis perpendicular to load and wood grain perpendicular to load. For the LRAA, LREA, I.RAE, LREE orientations, the sample sizes were 27, 22, 27, and 29, respectively. Results showed SG to be an acceptable predictor (r 2 =0.579) of ultimate tooth withdrawal strength for the LRAA orientation. However, neither SG nor percentage of latewood significantly influenced the location of tooth withdrawal. For the LREA orientation, SG alone was a good predictor (r 2 =0.834) of ultimate tooth withdrawal strength. Furthermore, the side of the joint test specimen where tooth withdrawal initiated was dependent on the wood piece with tire lowest mean SG. For the LRAE orientation, SG was a marginal predictor (r 2 =0.392) of ultimatetooth withdrawal strength. Forthe LREE orientation, SG was a goodpredictor (r 2 =0.607) of ultimate tooth-withdrawal strength.