Comparing full-length bending strength and small-scale test strength of western redcedar poles

In order to determine which small-scale strength properties best reflected pole bending strength, the strength of 1- by 1- by 16-inch beams removed from pole tops and butts, the longitudinal compression strength of 0.5-inch-diameter plugs removed at pole groundline, and Pilodyn-pin measurements taken at groundline were correlated with full-length strength tests of 11 western redcedar poles. Modulus of rupture (MOR), modulus of elasticity (MOE), work to maximum load, specific gravity, Pilodyn-pin penetration, and longitudinal compression strength of beams cut from pole butts correlated significantly with pole MOR at groundline and with pole MOE (r = 0.62 to 0.85). Longitudinal compression strength of plugs taken at pole groundline correlated significantly with pole MOR at groundline (r = 0.78) but not with pole MOE. Pilodyn-pin penetration at groundline, probably affected by pole surface checks and preservative treatment, did not reflect pole strength. Additional full-length strength tests of poles and small-scale tests are needed to develop a prediction model for estimating pole strength. Special adjustments should be made in the prediction model for poles with growth characteristics that affect full-length pole strength, such as spiral grain or nonuniform shape.

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