Axial compression behavior of bamboo-encased timber composite columns: Experimental and theoretical study

A novel bamboo-encased timber composite (BETC) column was proposed to enhance the compressive performance of conventional timber columns and achieve superior mechanical properties. Bamboo scrimber and Douglas fir were combined to fabricate BETC columns for experimental investigation. Axial compression tests were conducted on 27 composite columns, divided into nine groups, with varying cross-sectional configurations and slenderness ratios. The failure modes, axial displacement, lateral displacement, axial strain, ultimate bearing capacity, and stiffness of the composite columns were analyzed. The results demonstrated that the addition of bamboo scrimber significantly enhanced the ultimate load and initial stiffness of the columns, with the B20W20 configuration (49% bamboo proportion) achieving the optimal balance between strength, cost, and weight efficiency. Furthermore, the study revealed that the slenderness ratio had a pronounced effect on the buckling behavior and compressive capacity of the columns. In addition, a theoretical calculation method for the ultimate bearing capacity of composite columns was established based on the stability coefficient derived from NDS-2018 and the superposition theory for hybrid materials. Considering the incomplete interface force transfer efficiency, an interface shear strength correction factor was introduced, and its calculation formula was obtained by fitting experimental data. The predicted results using this improved theoretical method were in good agreement with the experimental values. These findings provide valuable insights for the design and application of bamboo-timber composites in sustainable construction.