Damage Tolerance of Longitudinal Cracks and Circular Holes in Wooden Beams: In load-Bearing Capacity Perspective

Cracks and holes are commonly found in wooden components, and ancient Chinese wooden buildings represented by Yingxian Wooden Pagoda demonstrate the ability to work with defects. This study systematically investigated the effects of longitudinal cracks and circular holes on the load-bearing capacity of wooden beams through four point bending experiments on 1580 samples. The study focuses on load-bearing capacity as the core indicator and provides calculation formulas for section weakening coefficient and damage tolerance coefficient to quantitatively evaluate the impact of cracks. Research has found that the harmfulness of damage strongly depends on its position within the wooden beam. In the horizontal direction, when the longitudinal crack is located in the pure bending section of the wooden beam, it has little effect on the load-bearing capacity of the wooden beam. Once it deviates to the transverse bending section, the load-bearing capacity of the wooden beam significantly decreases. The hole is most dangerous when it is located in the horizontal center of the wooden beam, and it is also dangerous when it is near the loading point. In the vertical direction, the crack has the greatest impact on the load-bearing capacity of the wooden beam when it is located in the neutral layer, while its impact decreases when it is close to the upper and lower surfaces of the wooden beam. Holes have the least impact when approaching the neutral layer, which is different from the impact pattern of cracks. In addition, the hazard increases when the hole is located in the tension zone of the wooden beam, and decreases when it is located in the compression zone. The anisotropy and fiber structure of wood are the microscopic basis for the damage tolerance mechanical behavior of timber beams.