RELATIONSHIPS BETWEEN LOBLOLLY PINE SMALL CLEAR SPECIMENS AND DIMENSION LUMBER TESTED IN STATIC BENDING

摘要

Prior to the 1980s, the allowable stresses for lumber in North America were derived from testing of small clear specimens. However, the procedures were changed because these models were found to be inaccurate. Nevertheless, small clear testing continues to be used around the world for allowable stress determinations and in studies that examine forest management impacts on wood quality. Using small clear and nondestructive technologies is advantageous because of the ease of obtaining and testing small clear specimens compared with lumber. The objective of this study was to compare mechanical properties in bending of small clear specimens with lumber specimens of loblolly pine. For this study, 841 pieces of lumber in the No. 1 to No. 3 grades and nominal 2 x 4 to 2 x 10 (38 x 89 to 38 x 235 mm) sizes were collected from a forest-through-mill study and tested in static bending. A small clear specimen (25 x 25 x 410 mm) was prepared from each piece of lumber and tested in static bending. The effect of growth ring orientation was explored, and overall, samples tested on the radial or rift face explained the variation in lumber more accurately than did samples tested on the tangential face. However, the relationships were generally poor for modulus of elasticity (MOE) (R-2 = 0.22) and modulus of rupture (MOR) (R-2 = 0.11) pooled data. A lumber-based multiple regression model explained 44% and 37% of the variability for MOE and MOR, respectively, whereas a stand-based multiple regression model explained 41% and 29% of the variability for MOE and MOR, respectively.