ABSTRACT This study investigated through‐diaphragm‐type beam‐to‐column connections of concrete‐filled steel tubular (CFST) columns with different upper and lower column sizes. Although tapered steel tubes can transmit stress smoothly, their fabrication is complex, and the strength of CFST beam‐to‐column connections with different upper and lower column dimensions has not been investigated. Experiments were conducted to examine the performance of connections with a column size discontinuity, where joint strength is governed by diaphragm plate deformation, and the bearing resistance of filled concrete was accounted for. Specimens representing interior, side, and corner column types were tested. The hysteresis behavior, diaphragm plate deformation, and stress transfer mechanisms were examined in detail. Furthermore, an ultimate strength evaluation formula that accounts for the bearing resistance of the filled concrete was proposed based on yield line theory. The analytical results were in relatively good agreement with the experimental results, demonstrating the validity of the proposed formula.
Fujinaga et al. (2026) studied this question.