Theoretical Axial and Lateral Stress–Strain Model for Steel Tube–Reinforced Concrete Column

Steel tube–reinforced concrete (STRC) columns are composite members consisting of an inner concrete-filled steel tube (ICFST) component and an outer reinforced concrete (ORC) component. These columns are commonly used in the bottom columns of high-rise buildings and bridge piers to withstand significant axial loads. However, the stress state of the components in a STRC composite column differs from that of a single confinement component. As a result, the existing lateral strain model and concrete constitutive model cannot be directly applied to describe the stress–strain development of each component. To address this issue, this study combines the existing confined concrete models with the stress balance condition and strain development characteristics of the cross section of a STRC composite column. Theoretical models are proposed to simulate the development of lateral strain and confining stress in both the ICFST component and ORC component. Additionally, the biaxial stress state of the steel tube is considered based on the generalized Hooke law and Prandtl-Reuss theory in the theoretical model. Consequently, an incremental iterative calculation model for the whole axial load–strain curve is proposed. The effectiveness of the proposed models is verified by comparing the calculation results with the experimental results.