The axial compression behavior of a new type of joint wherein the core concrete is confined by a core steel tube while the external concrete is confined by a ring stirrup is investigated in this study. Such a joint core is intended to connect a polyvinyl chloride-carbon fiber reinforced polymer–confined reinforced concrete column and reinforced concrete beam. The failure process and the effects of structural parameters on the mechanical behavior of the joint core are analyzed. Results indicate that the crushing of concrete in the joint core is the predominant failure modes of all specimens. The crack development speed is related to the specimen height and the reinforcement ratio of the core steel tube. The stirrup ratio does not significantly affect the crack development speed but can dominate the crack growth path partially during the crushing of the specimen. In addition, the ultimate bearing capacity of the joint core increases with the decrease in the specimen height, whereas it decreases as the stirrup ratio or reinforcement ratio of core steel tube decreases. Furthermore, a formula for predicting the ultimate bearing capacity of a joint core confined by a core steel tube is proposed based on dimensional analysis associated with the numerical simulations. This study is expected to provide preliminary guideline to facilitate such connection joint cores for structural systems.

In this paper, seven specimens were designed to study the influence of the height (h), width (b), and reinforcement ratio (ρ) of ring beam on the failure mode, bearing capacity, deformation, and equivalent stress–strain relation of joint core reinforced with ring beam for connection of polyvinyl chloride fiber‐reinforced polymer confined concrete column and reinforced concrete beam. The experimental results indicated that the crushing of concrete in the joint core dominated the failure of specimens. The ultimate, yield bearing capacity and axial strain decreased with the increase of height, while raised with the improvement of width or reinforcement ratio. The growth of the strains of reinforcement and concrete accelerated with the increment of height, while decelerated with the rise of width or reinforcement ratio. Subsequently, based on the local compression theory, confined concrete theory, and the principle of superposition of multiple confinement, considering the influence coefficient of joint height βh and the enhancement coefficient of stirrups αs, a new formula was proposed to estimate the ultimate bearing capacity of specimens under axial local compression. Then, on the basis of Mander's model, taking the correction parameter η into consideration, a new model of equivalent stress–strain relationship was established. Verification results showed that the models proposed in this research agreed well with the experimental results.