Enhancing Bamboo structural grading under axial compressive load: a comparative analysis of green and yellow bamboo

Abstract

This study enhanced the structural grading of two Sri Lankan bamboo species subjected to axial compressive loads. It created strength and capacity grading systems for Dendrocalamus giganteus (Green bamboo) and Bambusa vulgaris (Yellow bamboo). Bamboo exhibits nature's inventiveness by providing a renewable and environmentally beneficial alternative to conventional building materials. Its quick growth and adaptability make it ideal for sustainable buildings, particularly in hot, humid climates and earthquake- prone areas. Despite its strong performance bamboo’s full potential in modern building remains largely untapped due to insufficient design guidelines and the material's natural diversity. This work attempts to improve bamboo structural grading under axial compressive load whereas develop standardized testing and design methodologies by looking at the physical and mechanical properties of aforementioned two bamboo species. 60 samples from Green bamboo and 35 samples from Yellow bamboo were obtained to perform mechanical tests. Various diameters and ages were chosen to ensure sample representativeness. Compressive testing was performed adhering to ISO 22157 guidelines. The Universal Testing Machine measured compressive strength parallel to fibers. The maximum compressive loads (Fc) were recorded. Compressive strengths of bamboo samples were calculated by assuming hollow and solid circular sections (σcw and σcc, respectively). Linear mass (q) demonstrated a significant correlation with compressive force Fc, with coefficient of determination, R²=0.78, making it an excellent predictor for bamboo structural grading. The correlation between q and Fc was relatively low (R²=0.25) for yellow bamboo. Culm density and wall density were identified to be better predictors to estimate σcc with R²=0.69 and σcw with R²=0.68 in green bamboo. All the predictors indicate low R² values (R²<0.25) when predicting σcw and σcw of yellow bamboo. Results show that the compressive capacity of the bamboo can be predicted more accurately than the compressive strength. Hence capacity grading of bamboo is more effective comparing with strength grading.