Evaluation method of compression parallel to grain stiffness in wood and relationship between stiffness and shape of contact surface

The compressive behavior parallel to the grain is an essential parameter for the designing of multistoried and large timber buildings. However, the application of a compressive force parallel to the grain results in significant deformations near the end grain, which is referred to as the damage zone. Therefore, this study elucidates the mechanism of the damage zone and proposed a methodology to evaluate the properties of the damage zone. The cause of the damage zone was attributed to an uneven contact surface. As the contact surface shape remained non-flat even after reaching 28% of the predicted maximum load, the initial stiffness of compression parallel to the grain necessitated an assessment based on the influence of the damage zone. The Young’s modulus of the damage zone was approximately 2% of that of the middle zone and an evaluation method for the damage zone length was proposed using the strongest link model. The Young’s modulus and damage zone length evaluation methods were used to evaluate the stiffness of the specimens when compressed parallel to the grain. The proposed method could adequately evaluate the experimental values.