Hygrothermal Effects on Mechanical Properties of Lumber

As part of a parent study of possible environmental effects on the long‐term load‐carrying performance of structural lumber, the material characteristics of a lumber sample are evaluated in several hygrothermal states. The modulus of elasticity and modulus of rupture of sorted groups of select structural Douglas‐fir 2×4 lumber are determined from standard pseudostatic bending tests after the groups are brought into equilibrium with various prescribed environments. Lognormal statistical distributions of strength and stiffness of the various groups are related by evaluating the distribution parameters as quadratic functions of temperature and moisture content. The correlation between modulus of elasticity and modulus of rupture, and observed modes of failure, are also presented as they pertain to changes in temperature and moisture content.