Stress–strain relationship of concrete confined by rectangular steel tubes with binding bars

• The paper is a further study on the behavior of rectangular CFT with binding bars.
• A stress–strain model of concrete for rectangular CFT with binding bars is proposed.
• The binding bar arrangement in different directions is considered in the model.
• The failure criteria for concrete under triaxial compression are included.
• The proposed model is also applicable to rectangular CFT without binding bars.

This paper presents a model for uniaxial stress–strain relationship of concrete confined by rectangular steel tubes with binding bars. The difference between concrete confinement effect provided by broad faces and that provided by narrow faces of steel tube is considered in the proposed model. Also, the binding bar arrangement in different directions is taken into account in the model. The failure criteria for concrete subjected to triaxial compression is applied to estimate the ultimate strength of concrete core. The parameters of the model are determined based on the experimental results and the calculation of complete load–strain relationship curves is conducted for axially loaded rectangular CFT specimens with binding bars using this uniaxial stress–strain relationship. The concrete core strength and stress–strain behavior of rectangular CFT columns with binding bars is found to exhibit good agreement with experimental results. In addition, the proposed model is also applicable to concrete confined by rectangular steel tubes without binding bars.