Performance of Round-Ended Concrete-Filled Steel Tubular Columns Under Combined Compression–Bending–Shear Loading

This study develops and validates a finite element model for round-ended concrete-filled steel tubular (CFST) columns subjected to combined compression–bending–shear loading using ABAQUS. Based on the calibrated model, the mechanical behavior of such members is thoroughly analyzed, including lateral bearing capacity, axial force evolution, and interaction mechanisms. The influences of key parameters, such as shear-span ratio, axial load ratio, cross-sectional aspect ratio, concrete strength, and steel yield strength, on the bearing capacity are systematically investigated. Furthermore, a calculation method for predicting the ultimate bearing capacity is proposed based on the section equivalent approach. The results demonstrate that the loading direction relative to the principal axes significantly affects structural performance: long-axis loading leads to higher bearing capacity and improved ductility, whereas short-axis loading reduces the ultimate capacity by an average of 49%. As the shear-span ratio increases, the ultimate lateral capacity gradually decreases. For shear-span ratios between 1.0 and 3.0, the long-axis loaded specimens exhibit pronounced compression–bending–shear failure modes. Variations in the axial load ratio notably influence both lateral capacity and axial force distribution; both bearing capacity and ductility decrease with increasing axial load ratio, although the effect on ultimate capacity remains minor when the axial load ratio does not exceed 0.4.