The effect of detailed geometry reconstruction on the mechanical response of the French lap carpentry log joint - numerical analysis and experimental tests

The study focuses on traditional timber French lap joints commonly found in historical log structures in Europe. The analysed joints, used in the wall corners of log houses, consisted of five pine logs. Experimental load-bearing capacity tests were performed on a prototype testing stand using a biaxial strength testing machine, allowing rotation of one arm of the corner relative to the perpendicular arm. From the experiments, the relation between applied displacements and support reactions was obtained. The measured peak forces for the tested samples ranged from approximately 4.0 kN to 5.2 kN. The study also presents results of nonlinear static analyses performed using the finite element method for solid models of the investigated structures. A comparison between experimental results and numerical simulations was carried out for six joint models based on both idealised geometry and 3D scan-derived representations. The load capacity ratio of the idealised geometry model to the scan-based model was approximately 2. The highest correlation coefficient between the numerical results obtained for one of the models and the experimental data was R = 0.9426. The analysis examined the influence of log geometry and log arrangement on the mechanical behaviour of the tested timber joint, including stress distribution and joint deformation. Based on the analysis results, it can be concluded that accurately reproducing the geometry of the tested wooden elements can have a significant impact on the stiffness and load-bearing capacity of this type of carpentry joint.