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.

This paper presented a new joint core strengthened with multi-layer steel meshes for connecting the PVC-FRP Confined Concrete (PFCC) column and Reinforce Concrete (RC) beam. Seven specimens were tested under concentric compression and the effects of several parameters including the height, diameter of specimen and volume ratio of steel mesh on the compressive behaviors were investigated. Test results showed that all the reinforcement yielded successively and eventually the crushing of the concrete dominated the failures of specimens. The ultimate bearing capacity and ultimate equivalent axial strain decreased as the height of specimen increased, while they increased as the diameter of specimen or the volume ratio of steel mesh increased. The ultimate strains of all the reinforcement and concrete increased as the height of specimen increased while they decreased as the diameter of specimen or the volume ratio of steel mesh increased. Considering the influence of height of specimen, a modified formula for conveniently predicting the ultimate bearing capacity of the joint core strengthened with steel meshes was proposed based on the theory of confined concrete and superposition principle of multiple confinement. The predicted results were in good agreement with the experimental data. Additionally, an equivalent stress–strain relationship model of the joint core strengthened with steel meshes was suggested based on the experimental research. The predicted curves agreed well with the measured equivalent stress–strain curves. Moreover, a validated Finite Element (FE) model for the joint core strengthened with steel meshes was developed to conduct parametric studies, which broadened the available experimental results about the mechanical performances of the joint.

This paper presents an experimental study on mechanical behavior of Polyvinyl alcohol (PVA) fiber-recycled reinforced concrete (RC) one-way slabs. 21 specimens including 14 PVA fiber-reinforced recycled concrete slabs and 7 recycled RC slabs are fabricated and tested. The specimens are designed with different variables, such as replacement ratio of recycled coarse aggregate (RCA) γ, reinforcement ratio ρ_s, content of PVA fibers ρ_f, and span-to-thickness ratio I/h. The findings demonstrate that yielding of longitudinal reinforcement, breaking or pulling out PVA fibers along crack gaps and crushing of recycled concrete eventually dominate the failures of PVA fiber-reinforced recycled RC one-way slabs. The ultimate carrying capacity enhances as ρ_f or ρ_s increases, while decreases as I/h increases. The ultimate carrying capacity decreases with the increment of \(\rlap{--} \gamma \), while the introduction of PVA fibers can alleviate this weakening effect. The ultimate carrying capacity of RCB and PRCB decreases by 11.96% and 2.15%, respectively when the \(\rlap{--} \gamma \) increases from 0% from 100%. The ultimate deflection first increases and then decreases as ρ_s increases. Increasing γ, I/h or ρ_f increases the ultimate deflection. Comparatively, the variation of PVA fiber content has a more prominent effect on the ultimate deflection of PRCB-U. The ultimate deflection of PRCB-U and PRCB increases by 73.03% and 15.15% respectively when the content of PVA fibers increases from 1% to 2%. A verified finite element (FE) model for PVA fiber-reinforced recycled RC one-way slabs under static load is established on account of rational constitutive relationship of materials. Then, the parametric studies are carried out to further reveal stress mechanism and the impacts of five main influence parameters on mechanical behaviors are ulteriorly analyzed. Ultimately, several design recommendations are suggested based on the experimental and FE analysis results. The suggested content of PVA fibers is between 0.5% and 2% and the optimal reinforcement rate ranges from 0.49% to 0.59%.

Fibre reinforced polymer (FRP) is extensively applied in the field of maintenance and reinforcement. In the actual reinforcement of concrete structures, most reinforced concrete (RC) members are in a cracked state and the existing calculation methods seldom consider the initial damage of concrete, especially the effect of severe damage on the crack of RC members. Therefore, it is necessary to propose a model for accurately evaluating the crack width of the repaired different damage state concrete members with carbon fiber reinforced plastic (CFRP) sheet. This study presents an experimental investigation on the crack behaviors of the CFRP sheet flexural-strengthened pre-damaged RC beams based on the results of an experimental program involving ten specimens. The influence of the pre-damaged level, reinforcement ratio and CFRP sheet strengthening layer on the crack development, failure characteristics, crack spacing and crack width is analyzed and discussed. Taking into account the influence of the CFRP sheet strengthening layer and pre-damaged level, a formula for predicting the average crack spacing is proposed, and then an analytical model for the crack width prediction of the flexural-strengthened high pre-damaged beams is established based on the calculation model of the crack width of the ordinary RC beams. The predicted results agree well with test values including data of this study and experimental data of 64 sets of references.