Evaluation of the tensile strength of structural finger-jointed lumber.

Abstract

A study was undertaken to evaluate the tensile strength performance of both vertically and horizontally finger-jointed laminae with 3 different lengths of finger profiles for 5 softwood species. Douglas fir finger-jointed lumber showed the best joint efficiency at 74.1%, followed by spruce-pine-fir (SPF) groups, at 65%, among the 5 wood species. Both Japanese cedar and southern pine finger-jointed lumber had lower joint efficiencies due to weak finger profiles causing early failure in tension. Southern pine finger-jointed lumber was found to have the highest tensile strength, 116.6% higher than the lowest Japanese cedar group, followed by the Douglas fir group which was 65.9% higher. The hemlock and SPF groups had similar tensile strengths, and they were also higher than the Japanese cedar group by 46.8 and 40.7%, respectively. The tensile strength of lumber joined with a 21-mm long finger profile showed a significantly lower value than those with 18- and 24-mm finger profile groups by 11.3 and 8.5%, respectively, due to the wide finger tips. The results show that there was no significant difference in tensile strength of finger-jointed lumber between horizontal and vertical finger formation. With the exception of the 21-mm finger-jointed group, slightly higher tensile strength (7.4%) for the 18- and 24-mm finger length groups with vertical finger-joints was obtained, compared to those with horizontal joints.