Axial compressive behavior of novel laminated bamboo tubes: Experimental tests and predictive buckling model

Engineered bamboo materials reduce the inherent high variability in the geometry of natural bamboo, while offering enhanced and consistent mechanical properties. However, these materials often lose the distinctive aesthetic appeal of the original bamboo culms, which feature a hollow circular cross-section, rendering them indistinguishable to non-experts when compared with equivalent engineered wood materials. This study introduces novel laminated bamboo tubes that restore the efficient circular hollow cross sections of natural bamboo into engineered bamboo products. The novel manufacturing process of laminated bamboo tubes utilizes a hot-pressing technique and phenol formaldehyde adhesive to bond longitudinal trapezoidal bamboo strips into structurally consistent and aesthetically appealing circular hollow sections. This study experimentally investigated their axial compressive behavior, initially assessed the mechanical performance in terms of elastic modulus, parallel-to-grain compressive strength and perpendicular-to-grain tensile strength. A total of 144 specimens across three replications, with varying lengths, diameters, and thicknesses, were subjected to axial compressive loads to characterize their structural performance and assess the influence of slenderness ratio. The findings reveal two predominant failure mechanisms: hoop delamination (longitudinal splitting due to tension perpendicular to grain failure) in tubes with low slenderness and global buckling in long tubes, with intermediate behaviors observed in tubes of medium slenderness. The experimental results were adopted to calibrate a novel predictive model accounting for the non-linear effects and material anisotropy inherent in bamboo materials. This study paves the way for the application of these innovative tubes in actual construction projects, supported by a robust predictive model for instability buckling ready to be included in Standards and Code of Practice.