Stiffness of spruce wood - Influence of moisture conditions

In this paper stiffness measurements on 968 specimens, 11 x 11 x 200 mm(3), from Norway Spruce are presented. The measurements were carried out using a dynamic test method at equilibrium moisture content in 30% and 90% relati ve humidity. The test material, from two stands, was well defined with resp ect to growth conditions, material properties as knots and compression wood and position in the tree. Large variations in dynamic modulus of elasticit y 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 w as explained by occurrence of compression wood and knots. A strong individu al variation in stiffness between different trees was found. To achieve a m ore fundamental understanding of the relationships between stiffness and mo isture content it appeared that also microscopic characteristics need to be taken into account.