Brace-Beam-Column Connections for Concentrically Braced Frames with Concrete Filled Tube Columns

Abstract

Composite concrete filled tube (CFT) columns are advantageous for use in seismic resistant braced frame construction since these CFT columns are relatively inexpensive, stiff and strong. However, to utilize the composite behavior of the columns, the vertical component of brace force must be transferred through the beam-brace-column connection and distributed to both the concrete and steel in the column. Beam-brace-column connection details are critical for development of this composite action. This paper describes analytical and experimental studies carried out to better understand the transfer and distribution of force to the joint. A range of beam-brace-column gusset plate connections were considered. It is shown that the majority of force transferred from the steel into the concrete occurs by bearing rather than by friction. Steel gusset plates with horizontal ribs, or gusset plates with holes, allow more force transfer and have more composite action than plain gusset plates. Slip deformations between the steel and concrete are likely to be too small to mobilize the strength of shear studs in these connections.