General Engineer and

The purpose of our study was to define the influence of juvenile wood on the tensile structural performance of dimension lumber from fast-grown plantation pine wood. Ultimate tensile stress and modulus of elasticity were measured on nominal 2- by 4-in. (standard 38- by 89-mm) lumber from a 28-year-old fast-grown loblolly pine plantation in North Carolina. We compared four grades of lumber and two lumber lengths. Strength and stiffness decreased with increasing amounts of juvenile wood. Average ultimate tensile stress and stiffness values of pieces composed entirely ofjuvenile wood were from 45 to 63 % of those pieces composed entirely of mature wood, depending on grade and property. We used physical properties as grading criteria to conform our test material to 1988 National Design Specifications (NDS) allowable design values. For our test material, percentage of latewood, number of rings per inch (25.4 mm), specific gravity, and presence or absence of pith could not be used individually as successful criteria for assuring conformance to design values. We compared data on mechanical properties to 1988 NDS allowable design values and to In-Grade test values. The per-formance of the Select Structural lumber conformed closest to the NDS design values; in the thre