Unified stress-strain calculation model for UHPC-filled stainless-steel tubular columns with various cross-sectional shapes under axial compression

Different cross-sectional shapes of ultrahigh-performance concrete (UHPC)-filled stainless-steel tubular (UHPCFSST) columns result in their stress-strain curves exhibiting softening or hardening stages, and currently, there is no unified calculation model available that can effectively simulate these variations. Based on experimental data, models for predicting peak stress, peak strain, ultimate stress, and ultimate strain of UHPCFSSTs with high accuracy has been provided. Comparative analysis reveals that the stress transfer capability and stability of UHPCFSSTs with the different cross-sectional shapes from highest to lowest are as follows: circular, square, and rectangular. Building upon Wei et al.'s general stress-strain calculation model, a high correlation pattern between parameter b and hoop confinement coefficient (xi s) has been obtained through correlation analysis, elucidating the post-peak behavior of stress-strain curves of UHPCFSSTs. By modeling parameter b, Wei et al.'s model has been extended to accommodate the stress-strain relationship under axial compression for UHPCFSSTs with different cross-sectional shapes. This establishes a unified stress-strain calculation model for UHPCFSSTs with different cross-sectional shapes under axial compression. Comparative analysis indicates that the proposed unified calculation model for axial compression stress-strain behavior of UHPCFSSTs can effectively quantify the influence of cross-sectional shape on stress-strain curves, demonstrating high predictive accuracy and generality.