Numerical model for the behavior and capacity of circular CFT columns, Part I: Theory

This paper presents a simple and effective model for the behavior and capacity of circular concrete-filled tube (CFT) short columns under extreme loading conditions. Firstly, efficient methods are presented to predict the complete stress–strain curve of concrete and steel, which are subjected to triaxial and biaxial stresses, respectively. Empirical expressions are proposed for the confinement effect, which increases both the ductility and strength of concrete but decreases the yield stress of steel. Subsequently, the fiber model is adopted to describe the complete behavior of the CFT columns under axial force and bending moment. The accuracy and the applicability of the proposed method are examined in a companion paper.