Steel braced frame composite column connection behavior

Concrete placed inside hollow steel tubular columns, which are part of braced frame structures, can significantly increase the axial strength and stiffness of these columns. However, in order for the contribution of the concrete in the columns to be taken advantage of, forces applied to the columns through the braces must be effectively distributed to the concrete. The connection details between the brace and column are the key aspects of ensuring that this distribution occurs. Past connection designs vary widely, and their seismic behavior is uncertain. An analytical and experimental study is being carried out at the University of Washington to describe the behavior of these connections and their impact on global performance. As part of this study, an analytical study of the joint is carried out which is described in this paper. It is shown that for connections which involve a through-plate, the majority of the force is transferred into the concrete from the steel by bearing, rather than by friction. Also, slip deformations between the steel and concrete are too small to mobilize the strength of shear studs which may be used in the connection.