Abstract
With regard to moment-resistant frames installed by diagonal braces, the strong axial force is introduced into a column from diagonal braces at a beam-to-column connection. When the column is made of CFT (concrete-filled steel tube), the axial force from braces firstly transfer to the steel tubular portion of the column. If the steel and concrete composite action is expected, a certain component of the axial force should transfer to the filled concrete. Two types of stress transfer mechanisms may be available in CFT columns. The one is the concrete bond to steel tube, and the other is a mechanical shear key functioned by the cut-through diaphragm which is often used for beam-to-column connections in Japan. The paper presents the quantitative effect of diaphragm shear key and the evaluation method in practice.
