Prediction of Bending Strength of Yellow-Poplar 2 By 4’S from Estimated Strength Ratios

The bending strength ratio of each of 300 8-foot long yellow-poplar 2 by 4’s was estimated from knot size measured by displacement and on the worst face. Actual strength ratios were determined by testing. Linear regression analysis showed actual strength ratio to be more closely correlated with estimated strength ratio based on worst-face knot size than displacement knot size. Respective coefficients of determination were 27 and 17 percent. Actual strength ratios were greater than predicted for large knots and less than predicted for small knots. Correlation of modulus of rupture directly with estimated strength ratio did not result in a significant increase in explained variation. A more precise method appears to be needed for estimating bending strength of yellow-poplar.

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