Influence of culm position and regional growth conditions on the tensile strength perpendicular to the grain

Bamboo has received increasing attention as a sustainable structural material; however, its tensile strength perpendicular to the grain remains elusive in governing splitting failure, particularly in joint and connection design. This study experimentally investigates the tensile strength perpendicular to the grain of five bamboo species collected from three different regions and three culm positions (top, middle, and bottom). A total of 675 specimens were tested using the split-pin method in accordance with ISO 22157. The results demonstrate significant variability in tensile strength among the investigated species, reflecting the heterogeneous structure of bamboo. Variations along the culm height were also observed and are associated with differences in culm wall thickness and vascular bundle distribution. In addition, regional growth conditions influenced the mechanical performance of bamboo, indicating that environmental factors may affect the development of bamboo microstructure. Statistical analysis using one-way analysis of variance (ANOVA) revealed that regional origin significantly influenced tensile strength perpendicular to the grain for all investigated species, whereas the effect of culm position was significant only for selected species and remained comparatively modest based on post-hoc interpretation. Failure analysis showed that cracks generally initiated at the drilled loading hole due to stress concentration and subsequently propagated longitudinally along the fibre direction. Although splitting was the predominant failure mode, some specimens exhibited partial cracking, which may be attributed to variations in geometrical characteristics, fibre bundle distribution, and lignin matrix integrity. Overall, the findings contribute to improving the structural reliability of bamboo components and provide valuable insights into the variability and failure behaviour of bamboo subjected to transverse tensile loading, particularly in applications where tensile stresses perpendicular to the grain govern failure.