Axial compressive behavior of multi-cavity square concrete-filled steel tube stub columns

This study performed axial compression tests and used finite element method (FEM) to examine the effects of cavity number and wall thickness ratio of outer steel plates to inner cavity plates β on the compressive behavior of multi-cavity concrete-filled steel tube (CFST) stub columns. Experimental results demonstrate distinct failure mechanisms: single-cavity specimens exhibited catastrophic weld fractures triggered by continuous global buckling, while quadruple- and nonuple-cavity specimens developed localized half-wave buckling deformations owing to partition plate restraint. This mechanism significantly enhanced deformation uniformity and structural ductility, where specimens with β= 1.5 achieved the optimal ductility performance. Bearing capacity analysis quantified a 6.0 % higher ultimate load for quadruple-cavity specimens compared to single-cavity ones, whereas nonuple-cavity specimens demonstrated only a marginal 0.4 % improvement over quadruple-cavity ones. Bearing capacity of specimens with β= 1.5 exceeded those of specimens β= 1.0 and β= 2.5 by 28.0 % and 5.3 %, respectively. Evaluation of international design codes against experimental and FEM results proved the highest predictive accuracy of CECS 28:2012. Optimized design parameters include: β= 1.5, limiting number of cavities≤ 9, and core concrete strength restricted below C40 grade, based on rigorous validation of confinement effectiveness and material performance thresholds.