Finite Element Investigation of Square Steel Tube–High-Strength Spiral Stirrup Composite Confined Concrete Columns

Abstract

Square steel tube–high-strength spiral stirrup composite confined concrete (SHSCC) columns combine the advantages of external steel tube confinement and internal high-strength spiral reinforcement, offering considerable potential for improving the seismic performance of composite columns. However, systematic investigations of their cyclic compression–bending behaviour over a broad range of key design parameters remain limited, and the relative importance of these parameters has not been sufficiently clarified. In this study, a three-dimensional nonlinear finite element model was established in ABAQUS and validated against one experimental specimen in terms of hysteretic response, skeleton curves, ultimate lateral load and failure mode. The differences between the numerical and experimental peak lateral loads were 3.6% and 16.8% in the positive and negative loading directions, respectively, while the difference between the average absolute peak loads was approximately 7.5%. Based on the validated model, a comprehensive parametric study was conducted to investigate the influences of axial compression ratio, concrete strength, spiral spacing, spiral bar diameter and steel tube thickness on the cyclic behaviour of SHSCC columns. The results showed that increasing the steel tube thickness from 4 to 7 mm increased the ultimate lateral load, ductility coefficient and initial stiffness by 62.3%, 26.9% and 52.0%, respectively, indicating a pronounced beneficial effect of steel tube thickness within the investigated range. Increasing the axial compression ratio to 0.90 reduced the ultimate lateral load by 37.8% and the ductility coefficient by 31.8%, indicating a pronounced deterioration in cyclic performance at high axial compression levels. Increasing the concrete strength from C30 to C60 increased the ultimate lateral load and initial stiffness by 12.2% and 22.9%, respectively. In contrast, increasing the spiral spacing from 20 to 200 mm reduced the ultimate lateral load and ductility coefficient by 5.2% and 30.8%, respectively, whereas changing the spiral bar diameter from 8 to 12 mm produced only a 2.5% increase in ultimate lateral load. These results quantitatively clarify the relative effects of the principal design parameters on the cyclic response of SHSCC columns and provide numerical evidence for parameter selection and seismic performance optimization.