Comparative study on axial load capacity of PFCC column-beam joints with two different connection configurations

In this study, seventeen PVC-FRP confined Concrete (PFCC) column-beam joints including eight PFCC column - enlarged ring beam (ERB) joints and nine PFCC column-beam joints strengthened with Core Steel Tube (CST) are designed and tested. The failure modes, ultimate load capacity, deformation capacity of two different types of joints is compared and analyzed. The test results demonstrate that the failure processes of two different types of joints are basically similar, experiencing the elastic, crack development, yield and failure phases. Comparatively, the PFCC column-ERB joints enter the yield phase relatively earlier than the joints strengthened with CST. Both of the connection configurations can effectively constraint the concrete at the joints and significantly improve load capacity, showing their respective advantages. From the point of view of improving the connection efficiency of the joints, increasing ring beam width has the most obvious effect on the PFCC column-ERB joints, while reasonably reducing the height of joint has the greatest influence on the joints strengthened with CST. The axial equivalent ultimate strains of these two different types of joints are much higher than the ultimate compressive strains of ordinary concrete, indicating that both of the connection configurations can remarkably enhance the deformation capacity of the joints. By comparison, the deformation resistances of the PFCC column-ERB joints are greater than those of the joints strengthened with CST. In addition, taking into account the scale effect, a comprehensive influence coefficient of the joints is introduced, and a unified formula for estimating the axial load capacities of the two different joints is proposed based on a modified superposition approach and validates the test data of this paper and other references with good agreement.