ANALYSIS AND DESIGN OF AXIALLY LOADED SQUARE CFST COLUMN TO RC BEAM JOINTS STIFFENED BY DIAGONAL RIBS

Abstract

This work proposes a partially through-beam joint system to connect square concrete-filled steel tubular (CFST) columns and reinforced concrete (RC) beams. In the system, the holes in the steel tube allow longitudinal beam reinforcements to be continuous through the joint zone to achieve direct load-transfer of the beam, and the square steel tube with holes is strengthened by welding diagonal ribs located at the corners of the steel tube. Finite element (FE) analyses on joints with RC beams were carried out based on verified models. The analysis results showed that diagonal ribs welded to the joint tube confined the concrete in the joint zone efficiently and made up for the reduction in axial load capacity caused by the holes of the steel tube, so the joint system can meet the requirements of strong-joint weak-component under axial compression with ease. Finally, mechanics-based models and axial strength equations of joints were proposed, and the predicted results agreed well with the FE results. These results proved that the square CFST column to RC beam joints stiffened by diagonal ribs were feasible and can be applied in engineering practice based on reasonable design.