Proposed strength formula for concrete-filled square hollow tubular section column-beam pinned connections

The higher a building, the more concrete-filled square hollow tubular section column-beam connections are applied. The RC core and exterior concrete-filled tubular (CFT) column-beam pinned connection is one of the structural systems that support lateral load. If this structural system is used, due to the minimal CFT column thickness compared to that of the CFT column width, the eccentric distance of the column flange surface and connection degrades the strength by the local moment on the column flange surface. This study performed a finite element analysis on the CFT column-beam pinned connection to determine the strength degradation of the CFT column. The column's width and thickness were used as variables for the analysis. To guarantee the reliability of the finite element analysis, an actual-size specimen was fabricated and tested. The yield line theory was applied in the proposed strength formula for the CFT column-beam pinned connection. Based on the study's results, the strength improved with the increase in the column's size, which suggested the limitations of the concrete-filled square tubular column type without internal reinforcement. If the limitation value is not satisfied, the reinforcement inside the column is mandatory. The form of the horizontal stiffener was proposed along with the strength increase of the concrete-filled square tubular column and simplification of its fabrication process. The formula for the strength of the CFT column-beam pinned connection, which factors the strength decline, is therefore proposed both for columns with and without internal horizontal reinforcement.