Improved bending strength of Douglas fir (Pseudotsuga menziesii) timber relative to Japanese larch (Larix kaempferi Carr) grown in Korea

Small-diameter logs are intended to function as high-value structural timber. Bending strength properties is an essential phenomenon for structural lumber. Herein, the modulus of elasticity, the modulus of rupture and the allowable bending stress (ABS) of domestic (Korea) small and large-diameter larch and large diameter Douglas fir timber were measured and compared according to the standard of ASTM D 2915. Samples were visually graded as Grade 1 to Grade 4 following the provisions included in KS F 3021.2013. The large-diameter Douglas fir timber (Grade 1 to Grade 4) exhibited the highest MOE value, but in Grade 4, it showed the lowest MOR value compared with the small and large diameter of larch timber. The ABS of small-diameter larch was 12.0 MPa, higher relative to KBC 2009 Grade 1 structural lumber (8.0 MPa). The ABS of large-diameter of larch and Douglas fir timber exhibited 15.5 and 18.1 MPa, respectively.