Relationship between the mass profile and the strength property profile of decayed wood

To resolve degradation problems of timber structures, analysis of the development of a fungal attack on structural timber is important. The progression of wood decay especially that of structural timber is not always uniform and reduces strength locally. Therefore, the strength profile is important in estimating the strength of decayed wood. In this study, Sitka spruce (20 mm x 20 mm x 100 mm (longitudinal direction)) was exposed to brown- and white-rot fungi for 3 to 15 weeks from the end surface. After decay, mass profiles of an oven-dried specimen were obtained by X-ray densitometry, and specimens for compressive and tensile tests were cut from the decayed wood to determine both compressive and tensile strength distribution profiles in the longitudinal direction. Except for some results of the tensile strength, after 3 weeks treatment with brown-rot fungus, both strength and mass were reduced. For the same decrease in mass, the tensile strength was reduced more by the brown-rot fungus than by the white-rot fungus, whereas the results for compression strength were almost the same for the two fungi. The results suggested that it is possible to estimate the strength loss of the decayed wood from the mass profile.