Shear mechanism of RCS joints with whole column-section diaphragm

Abstract

The authors proposed a new precast RC column-steel beam (RCS) joint with whole column-section diaphragm, aiming to address the shortcomings including bearing failure and difficulty in prefabrication of the RCS joint details available in the existing literature. Due to its unique details, the proposed RCS joint may have a dissimilar force-transferring mechanism from the conventional beam-through type RCS joint. Moreover, the effect of various parameters on this novel joint was still unclear by limited test results. The objective of this study was to clarify the shear mechanism of the proposed joint and the impact of critical parameters. Specimens with different axial load ratios and thickness of parallel FBPs were tested under cyclic loading. The results showed that the increase in axial load ratio and thickness of parallel FBPs improved joint strength in this test. A detailed three-dimensional finite element (FE) model was developed and verified using the experimental results. The difference in the force transferring between the proposed joint and conventional beam-through RCS joints was explained in detail based on the numerical results. The dowel action of longitudinal column bars were evident in the proposed joint and the orthogonal FBPs were ineffective in activating the inner concrete strut. A parametric study was further conducted. The impacts of width of parallel FBPs, thickness of orthogonal FBPs, and axial load ratio were investigated. The joint strength linearly increased with the width of parallel FBPs. A parabolic distribution of shear stress in the parallel FBP section was obtained, while the yield zone was concentrated in the central area of the parallel FBP. The ductility could be improved with the thickness of orthogonal FBPs when the thickness was less than 10 mm. Further increasing the thickness of orthogonal FBP beyond 10 mm did not significantly affect the overall joint behavior. The joint may attain the optimal shear strength when the axial load ratio is between 0.3 and 0.4. The modeling approach in this study could be adopted as an effective tool to assess joint behavior. Moreover, the conclusions obtained by numerical study potentially promoted the application of the proposed joint.