Influence of slenderness ratio and eccentricity on the load-bearing capacity of laminated bamboo lumber (LBL) columns derived from Bambusa spinosa Roxb

Sustainable structural options are needed as conventional materials face supply and carbon constraints. We examined laminated bamboo lumber (LBL) columns manufactured from Bambusa spinosa ( kawayang tinik ) and quantified how the slenderness ratio ( λ ) and eccentricity-to-height ratio ₀ ( e ₀ / h ) affected the ultimate capacity under eccentric compression. The mechanical properties used in the analysis were parallel to grain. Prismatic LBL columns (50 ×50 and 25 ×25 mm; clear heights, 300, 450, 600 mm) were tested under quasi-static displacement control (0.5 mm min -1 ). Axial load, including prescribed eccentricities, was introduced through bonded steel end brackets that provided uniform bearing and pinned-like end conditions; offsets were verified prior to loading. There was a clear inverse relation between λ and capacity, reflecting increased buckling susceptibility with slenderness, and a pronounced sensitivity to ₀ e ₀ / h consistent with combined compression–bending. Based on the dataset, a species-specific empirical equation is proposed that integrates λ and ₀ e ₀ / h . Predictions clustered near the identity line with MAE = 1.35 kN, RMSE = 1.69 kN, and MAPE = 9.09% over the tested range (approximately λ ≈ 21 − 83 ; ₀ e ₀ / h ≈ 0.042 − 0.167 ), exhibiting a small conservative bias desirable for design. A benchmark against a published model indicated comparable accuracy while preserving local calibration to B. spinosa . In contrast to prior LBL studies that largely feature Phyllostachys pubescens and single-eccentricity tests, this work provides a dedicated B. spinosa dataset, examines multiple eccentricities together with slenderness, and delivers a calibrated, validated capacity model with a stated domain of applicability. The findings offer design-oriented, species-appropriate guidance for the structural use of engineered bamboo in Philippine practice and similar contexts.