Structural behavior of beam-to-column connections of circular CFST columns by using mixed diaphragms

Abstract

Concrete Filled Steel Tube (CFST) is a structure made of a steel tube filled with concrete, in which the rigidity of the member can be increased as the steel tube confines the concrete and the concrete reduces the local buckling of the steel tube. The object of this study is a mixed diaphragm which uses a penetrated diaphragm and an exterior diaphragm in combination at beam-tocolumn connections of circular CFST columns to improve the concrete filling property. Verifying that the resistance force of mixed diaphragm is same as or superior to that of current type, the study has been conducted on the optimal dimension of mixed diaphragm of which the validity and superiority at connections of circular CFST structure have been confirmed. A size of the circular CFST column of which the yield moment is bigger than that of the beam has been selected. A type of circular CFST which exceeds the yield and full plastic moments of the beam and satisfies the condition of maintaining the initial rigidity and the maximum resistance force has been selected through finite element analysis, and a regression analysis has been conducted to obtain an approximate expression used to calculate the optimal diaphragm. The reliability and validity of the obtained approximate expression have been confirmed through a statistical theory based analysis and an approximate plane analysis. This approximate expression can be used to calculate the optimal size of the mixed diaphragm required at the beam-to-column connection of a circular CFST column.