Revisiting the Compression Parallel to Grain Design Values of Douglas-Fir

After the decrease in southern pine (Pinus spp.) design values, concerns were raised over the design values of Douglas-fir (Pseudotsuga menziesii), the most important structural species in the Pacific Northwest of the United States. Moreover, species need to be re-evaluated every 5 years for properties by the grading agencies. Variability within Douglas-fir lumber may have increased over time because of changes in the silvicultural practices and management techniques including the shift from government to private plantation. The compression parallel to the grain design values took the greatest hit for southern pine. To assess if there is any decrease in the compressional design values, No.2 grade Douglas-fir, of dimensions 38 by 89 by 2,438 mm, were attained from 36 different locations and were cut into 229-mm sections with 20 samples from each location. A total of 720 samples were tested to failure in compression parallel to grain according to ASTM International D4761. Additionally, 288 clear specimens were also tested. The compression strength was calculated and was compared among locations. The data were pooled to calculate the design values for compression parallel to the grain and compared with listed values in the National Design Specification. Variation of compressive strength within locations was observed, but even after accounting for the variation the calculated values are above the average reported value for clear wood specimens and higher than the code-recommended design value for nonclear specimens.