EFFECT OF CYCLIC HUMIDITY EXPOSURE ON MOISTURE DIFFUSION IN WOOD

It is known that moisture content changes in wood strongly affect the mechano-sorptive effects, which in turn contribute significantly to th e deformation and strength under long duration loads. Earlier studies have shown that the moisture changes due to the daily and annual varia tion in the surrounding air tend to be confined to the edges of practi cal size members. Therefore, prediction of the moisture content near t he boundaries of a timber section becomes an important issue. This pap er studies the mathematical solutions of the diffusion equation for th e finite thickness element considering the effect of surface resistanc e. By introducing a surface attenuation factor, a simple approximate s olution may be obtained. Procedures for evaluating the coefficients K and D are also discussed, together with some data on these values for radiata pine (Pinus radiata). The surface emission coefficient K is a function of air velocity V. A procedure for assessing this effect of t he air velocity is also given. A numerical example shows that the prop osed approximate solution accurately predicts the cyclic range of mois ture content for an ambient cyclic boundary condition. The procedures described herein can be easily extended to include the analysis of two -dimensional and three-dimensional elements.