Considering wood defects in the structural analysis of bending wooden elements

Wood is a natural material widely used in construction. Unlike artificial building materials, wood is characterized by natural defects (flaws) that can negatively affect its performance under load. This study proposes a model for calculating the strength and deformations of bending wooden structures based on material deformation diagrams, allowing the consideration of natural wood defects, such as knots. The model accounts for the physical nonlinearity of wood deformation under compression and the presence of materials with different deformation diagrams within the analyzed cross-section, enabling stress redistribution at all stages of loading, up to failure. Theoretical calculation results obtained using proposed method were compared with the own experimental test results and with experimental data, obtained by others. The findings of the experimental and theoretical study confirm the feasibility of applying the diagrammatic approach to calculate the bending strength of wooden structures with defects (knots). This approach involves modeling the deformation of knots under compression using a parabolically linear diagram with a maximum ordinate equal to the resistance of the main wood perpendicular to the grain, while neglecting the tensile performance of knot wood. In addition to evaluating the strength and deformability of wooden elements in buildings under construction or in use, the proposed consideration of wood defects in the form of knots will facilitate the justified rejection of defective wooden elements during sorting.