Longitudinal compression: a measure of wood strength

Longitudinal compression strength (LCS) of plugs (0.5 in. diameter) removed from Douglas-fir beams (1 by 1 by 16 in.) was studied for its relationship with the bending-strength properties of the beams. The utility of LCS as a predictor of ultimate bending strength (MOR) was compared with that of Pilodyn pin penetration, radial compression strength (RCS), and specific gravity (SG) or density (D). LCS measured at 0.06-inch plug compression accounted for 54 to 66 percent of the variation in beam MOR. Slopes of regression equations predicting beam MOR from LCS measurements were statistically the same for untreated or preservative-treated wood, and sound or degraded wood. LCS was more accurate than Pilodyn pin penetration or SG for predicting beam MOR over a wide range of residual strength. RCS was not related to strength of sound Douglas-fir having a narrow strength range but was a better strength predictor than the Pilodyn or SG for decaying beams. LCS was the only predictor variable examined that reflected the reduced MOR of ammoniacal copper arsenate (ACA)-treated sapwood, as compared to MOR of adjacent untreated heartwood. LCS is useful for estimating wood strength of small beams; a study is needed to relate LCS of plugs to the strength of full-sized members and a field method for measuring LCS should be developed.

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