Abstract: A three-dimensional elastoplastic damage constitutive model for concrete and the arc-length method are used to analyze the confining effect of stirrups in reinforced concrete under uniaxial compression. The uniaxial compressive strength and ductility increasing coefficients of confined concrete are then obtained. Based on the framework of damage mechanics of continuous media, the uniaxial compressive strength and ductility increasing coefficients of confined concrete are introduced. An elastoplastic damage constitutive model for confined concrete under uniaxial load is proposed. The analysis showed that the proposed model was in accordance with the thermodynamic equation. In addition, the increase of strength and ductility, strength softening, stiffness degradation, residual deformation, and crack effect of confined concrete can be obtained by the proposed model. The parameters of the proposed model use the same parameters of the constitutive model in the concrete design code. Therefore, the proposed model is suitable for engineering applications. The proposed model combined with fiber Timoshenko beam elements is implemented in the structural nonlinear analysis software package ‘SAUSAGE’ by independent development. A reinforced concrete frame is analyzed by SAUSAGE. The results show that the confining effect of stirrups could effectively restrain the development of nonlinearity of beam and column members, and reduce the global indexes such as the maximum story drift ratios and maximum story shear force.