New axial Stress-Strain model of square concrete columns confined with lateral steel and FRP

Due to its efficiency, Fiber Reinforced Polymers (FRP) jacketing has become a common practice for confining concrete columns that need increased axial strength, axial ductility or shear capacities. The presence of confining lateral steel in columns, when externally retrofitted with FRP, changes the mechanism of concrete behavior. The interaction between lateral and longitudinal steel and FRP jacketing redistributes stress concentrations in concrete and yields more complex effective confined area compared to that of plain concrete confined with either FRP or lateral steel alone. Square columns confined with lateral steel and FRP are not well-addressed in the literature compared to circular columns. Therefore, this research focuses on square columns confined with lateral steel and FRP sheets through reviewing existing models in the literature and benchmarking their performance against experimental cases of square columns using axial stress-strain diagrams. Moreover, statistical analysis conducted for theoretical peak strength and ultimate strain obtained from the available models highlight their comparative performance which can be further improved. Therefore, this paper proposes a new model that overcomes shortcomings found in the reviewed models and predicts peak strength and ultimate strain more accurately.