EXPERIMENTAL ASSESSMENT OF THE EFFECT OF LENGTH ON THE TENSILE-STRENGTH OF STRUCTURAL FINGERJOINED LUMBER

The effect of specimen length on the strength of fingerjoined lumber i s incompletely documented in the literature. The objective of this stu dy was to experimentally assess the effect of length on tensile streng th parallel to the grain in fingerjoined structural lumber. The effect of length was observed for 38- by 89-mm (2- by 4-in.) fingerjoined lu mber members made of short kiln-dried black spruce lumber segments of 1.32 and 1.83 m (4.3 and 6 ft.) in length complying with the requireme nts of the 1650f-1.5E and the 2100f-1.8E machine stress-rated (MSR) lu mber grades. Tests were performed on specimens made of 4 and 6 segment s fingerjoined together producing members of 6.10 and 8.53 m (20 and 2 8 ft.) in length, which were tested over gauge lengths of 4.88 and 7.3 2 m (16 and 24 ft.), respectively. For each grade(1650f-1.5E and 2100f -1.8E), an additional group from a previous study of specimens made of two segments producing members of 3.66 m (12 ft.) in length and teste d over a gauge length of 2.44 m (8 ft.) was used in the assessment of the effect of length. The length effect factors (g(L)) obtained for bo th MSR grades of fingerjoined lumber appear to be considerably higher than the g(L) values for unjoined visually graded lumber reported in t he literature. The length effect factor at the 5th percentile was foun d to be more significant for the 2100f-1.8E grade (g(L) = 0.33) than t he 1650f-1.5E grade (g(L) = 0.30) because a better fit on the regressi on line was obtained. The average tensile strength for the 1650f-1.5E tends to converge to the value of 24 MPa at longer lengths. This sugge sts that the linear logarithmic theory may not be the more efficient m ethod for the evaluation of the effect of length in structural fingerj oined lumber.