Strength of Second-Growth Douglas-Fir in Tension Parallel to the Grain

Results of this study produced two averages for tensile strength of second-growth Douglas-fir, one for material at 12 percent moisture content and the other for unseasoned material. Based upon results from testing 529 specimens, strength of second-growth wood appeared to be comparable to that of old- growth Douglas-fir in tension. Specific gravity averages indicate that second-growth material could produce wood with as high a specific gravity as that published for old-growth wood. When growth rate was not considered, tensile strength increased as specific gravity increased. The average tensile strength of second-growth Douglas-fir was 161 percent higher for wood at 12 percent moisture content and 141 percent for unseasoned wood than published modulus of rupture values for old-growth wood. The results are based on tests in a 20,000 pound Tinius Olsen testing machine under continuously applied load to destruction.

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