Strength of Western Hemlock Compared for Two Areas

A statistical analysis was made to determine if differences occurred in basic strength properties of Tsuga heterophylla randomly sampled from Clatsop County and that part of Mt. Hood National Forest west of the summit of the Cascade mountains. Strength tests were conducted according to D-143-52 of ASTM. The average specific gravities, 0.38 and 0.39 for Clatsop and Mt. Hood respectively, were not significantly different. Significant differences between sample areas of various strength properties were determined by analysis of variance. The only notable differences in average properties from the two areas were fiber stress at proportional limit in static bending and compression parallel to the grain at the grain at the 2-1/2 percent significance level, and modulus of rupture at the 1 percent level. Averages for western hemlock from Mt. Hood were higher. For the combined areas, shear strength along a tangential surface was higher than along a radial surface at the 1 percent significance level. Simple linear regressions for modulus of rupture on specific gravity were different at the 5 percent level of significance. All properties in compression parallel to the grain were different at the 1 percent level. For combined areas, the slope of the regression line for radial shear on specific gravity was different from the slope for tangential shear at the 1 percent level.

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