Modulus of Rupture and Dynamic and Static Modulus of Elasticity of Eastern Cottonwood Two-By-Fours

MOR and apparent static MOE were calculated and recorded with the corresponding dynamic MOE values. The three variables were analyzed by a least squares regression procedure. A high correlation was found between static MOE and dynamic MOE. The regression line explained 83.6 percent of the variation. Previous studies showed similar results. Lower correlations resulted when static and dynamic MOE were used to predict MOR. The regression line for MOR vs. static MOE explained 61.2 percent of the Variation. This coefficient of determination corresponds closely with data obtained using small clear green specimens. The regression line for dynamic MOE vs. MOR explained 45.6 percent of the variation. The inclusion of SG in the MOR regression equations had no effect on either the correlation coefficients or the standard errors of the residuals. The dynamic MOE values for the 184 2 by 4’s were placed in the proper regression equations to predict static MOE and MOR for each 2 by 4. Of the 184 pieces for which static MOE values were predicted, only 7 had values of dynamic MOE that fell outside the range of data from which the regression was developed. For the predicted static MOE values, the mean was 1.52 million pounds per square inch and the standard deviation was 0.2013 million pounds per square inch. For the predicted MOR values, the mean was 7,392 pounds per square inch and the standard deviation was 1,369 pounds per square inch. These predicted values compare well with the actual destructive test data.

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