Stiffness of spruce wood – Influence of moisture conditions

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, from Norway Spruce are presented. The measurements were carried out using a dynamic test method at equilibrium moisture content in 30% and 90% relative humidity. The test material, from two stands, was well defined with respect to growth conditions, material properties as knots and compression wood and position in the tree. Large variations in dynamic modulus of elasticity between the two moisture levels were found. For specimens from some trees, these variations were extremely large. The variations were not systematic within each tree as many other wood parameters. A part of the variations was explained by occurrence of compression wood and knots. A strong individual variation in stiffness between different trees was found. To achieve a more fundamental understanding of the relationships between stiffness and moisture content it appeared that also microscopic characteristics need to be taken into account.