A unified method for predicting cross-sectional capacity of confined CFST columns

Concrete-filled steel tubular (CFST) columns may experience reduced cross-sectional capacity due to environmental and accidental actions. External confinement retrofitting methods (ECRMs), such as fiber reinforced polymer (FRP) fabric bonding and tube-grout confinement schemes, offer practical strengthening solutions. However, existing calculation methods are typically limited to specific cross-sectional shapes or confinement schemes, with complex formulations or lacking general applicability. This paper develops a unified calculation method for predicting the cross-sectional capacity of confined CFST columns with various cross-sections (circular, square, and rectangular) and confinement schemes (FRP fabric external bonding, FRP tube-grout confining, and steel tube-grout confining). Comprehensive validation against a database of 277 experimental results demonstrates good prediction accuracy, with 70 % of predictions within ±13 % relative error. The proposed unified framework eliminates the need for multiple calculation approaches, providing engineers with a practical tool for design of strengthened CFST columns under diverse service conditions.