Tensile Strength of Special Douglas-Fir and Hem-Fir 2-Inch Dimension Lumber


  • James W. Johnson
  • Robert H. Kunesh


<i>Pseudotsuga menziesii</i>, <i>Tsuga heterophylla</i>, <i>Abies spp.</i>, edge knots, center knots, single knots, multiple knots, specific gravity, modulus of elasticity, skewed distributions, strength tests, lumber strength


Nominal 2- by 4-, 6-, 8-, and 10-inch Douglas-fir and hem-fir dimension lumber was tested in tension parallel-to-grain. Five hundred ninety-three pieces of hem-fir and 563 of Douglas-fir were included in various categories of none, single small and large center and edge knots, and multiple knots. Tension stress, specific gravity, and modulus of elasticity in flatwise bending decreased as width of lumber increased. Tensile strength decreased with increased knot size. Pieces of lumber with single center knots occupying 21% of the width were similar in tensile strength to pieces of lumber with single edge knots occupying 14%. Pieces containing several small knots, well scattered, were as strong in tension as those with single small knots. Tensile strengths of Douglas-fir and hem-fir were not significantly different. In estimating lower exclusion values, adjustments should be made for skewed distributions. One method is suggested.


Kunesh, R. H. 1966. Grips for tension tests of structural-size lumber. For. Prod. J. 16(6):60.nKunesh, R. H., and J. W. Johnson. 1972. Effect of single knots on tensile strength of 2- by 8-inch Douglas-fir dimension lumber. For. Prod. J. 22(1):32.nKunesh, R. H., and J. W. Johnson. 1974. Effect of size on tensile strength of clear Douglas-fir and hem-fir dimension lumber. For. Prod. J. 24(8):32.nWarren, W. G. 1974. Comparison of exclusion values for lumber strength. Wood Fiber 6(3):237-241.n






Research Contributions