Research on the mechanical performance of circular concrete‐filled steel tube columns under bending‐torsional coupling

Under the influence of wind and horizontal seismic forces, structures such as piers in curved beam bridges, main arches of steel tube concrete arch bridges, and frame columns may experience combined bending‐torsion stress states, affecting the safe usage of the structure. To investigate the mechanical performance of circular concrete‐filled steel tube(CFST) columns under bending‐torsional coupling, a three‐dimensional solid‐shell finite element model of circular concrete‐filled steel tube columns under various bending and torsion ratios (k) was established using ABAQUS software, and validated with existing experiments on such columns under bending‐torsional loading. Parametric analysis was conducted to explore the trends of interface slip and the restraining effect in circular concrete‐filled steel tube columns under different bending and torsion ratios, analyzing the impact of parameters such as the yield strength of steel, concrete strength, steel content in the cross‐section, and shear–span ratio on the combined bearing capacity. The results of the parametric analysis show that: (1) with the increase of k, the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (2) the relative slip at the interface between the core concrete and the outer steel tube first increases and then decreases, with interface slip leading to a reduction in the load‐bearing capacity; (3) with the increase of k, the circumferential and axial stresses in the steel tube surface of the circular concrete‐filled steel tube columns increase, while the shear stress decreases, leading to a transition in the failure mode of the columns from combined bending‐torsional failure to bending‐shear failure. Based on these findings, a practical calculation formula for the bending‐torsional combined bearing capacity of circular concrete‐filled steel tube columns is proposed, offering high calculation accuracy and serving as a reference for the design of such components.