The Effect of Specific Gravity and Growth Rate on Bending Strength of Finger-Jointed Southern Pine

Christopher D. Knowles, James D. Stamey, Edward F. Dougal


In this study, the effect of specific gravity and rings per inch on the bending strength of 11 mill-run batches of finger-jointed southern pine lumber was examined. The bending test specimens were prepared according to the Glued Lumber Standard for Southern Pine as outlined by the SPIB. For each fingerjointed board, 8 wood properties were calculated. The 8 wood properties were maximum, minimum, average, and differential specific gravity; and maximum, minimum, average, and differential rings per inch. Multiple linear regression analysis was used to examine the effect of these wood properties on the bending strength (MOR) of the lumber. This relationship was examined for test specimens subjected to an accelerated aging cycle and those not subjected to the cycle. Coefficients of determination (r2) ranged from 0.06 to 37. For both specific gravity and rings per inch, the differential specimens had the lowest r2 values, and the average specimens had the highest r2 values. The relationships found in this study are consistent with strength-wood property relationships for finger-jointed and solid wood specimens reported in previous literature.


Finger-joint;specific gravity;rings per inch;southern pine;modulus of rupture

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