Panel Zone Behavior of Moment Connections Between Rectangular Concrete-Filled Steel Tubes and Wide Flange Beams

During the 1990s, guidelines for the detailing of composite joints for seismic safety have been proposed and adopted. Such guidelines were based on the testing of composite joint subassemblies under cyclic loads. The role of the confined concrete core in composite joints has been documented and quantified for systems using steel shapes encased in concrete, as well as for other mixtures of reinforced concrete and structural steel. The need to understand the role of the concrete core in moment connections utilizing concrete-filled tube (CFT) columns still exists.

In this research program, the split-tee through-bolted moment connection between wide-flange steel beams and concrete-filled tubes was studied. The aim of the study was to understand the role of the confined concrete core in transferring forces through the joint. Fifteen half-scale panel-zone specimens were designed and tested to model the shear behavior of the split-tee connection. Following an analysis of the results of the panel-zone tests, six full-scale moment connections were designed and tested. Variables studied were: concrete compressive strength , the b/t ratio (slenderness) of the steel tube walls, and the split-tee contact area against the steel tube.

Following an analysis of the test data, design criteria for the concrete contribution to the joint strength are presented, and recommendations are made for the inclusion of CFT systems in the design recommendations for composite joints. Suggestions are made for further research.