Keywords: connection, joint, tube, concrete-filled, finite element, circular column.

Concrete-filled tube (CFT) columns have been widely used and studied for decades since the CFT columns possess an excellent axial load-carrying capacity and ductility, especially for the circular CFT columns. However, litter research [1,2] has been conducted on the behaviour of the connection joining the circular CFT column. The beam-to-column connections shall retain sufficient strength and ductility to resist the possible seismic load. In this paper, the analytical investigation of behaviour of connections between steel beam and concrete-filled circular steel tube column is presented.

Finite element analyses [3] were conducted to investigate the force transfer mechanism of various configurations of connection details. An exterior T-shaped beam-to-column connection subassemblage was modeled to analyze the effect of the parameters as well as the behaviour of the connections. Eight-node shell element was used to model the steel tube and structural beam, and the uniaxial elastic-plastic stress-strain relationship was assumed for steel material. An eight-node three-dimension solid element was adopted for the concrete core. Both the built-in concrete material model and simplifying stress-strain relations were employed to model the concrete material due to the consideration for computational convergence problem. The confinement effect of the concrete core provided by the steel tube was ignored. Moreover, a surface-based contact method was implemented to model the interface between concrete core and steel tube. The interface was assumed to simulate the physical phenomenon when the tube is subjected to tension and compression flange forces.

The experimental results [4] were adopted to verify the validation of the finite element modeling. Behaviour and the force-rotation relations of the connection specimens were compared to the analytical results. Good agreement between experimental and analytical results is obtained. This study demonstrates that failure behaviour of steel beam to circular CFT column connections can be predicted using nonlinear finite element analysis.

The analytical results for various connection details indicate that the concrete strength has an insignificant effect on the moment-rotation relations of the joints. The convergence problem is attributed to the stress-strain relations of the concrete material. Large diameter-thickness ratio of the tube results in high potential distortion of the tube wall that will lead to the premature failure of the joint. The connection of beam directly welded to the steel tube cannot develop the required flexural strength due to the distortion of the tube wall. Both external diaphragm and side plate reinforced connections possess the sufficient flexural strength since the beam flange forces can be effectively transferred to and resisted by the concrete core inside the steel tube.

1

Azizinamini, A., Shekar, Y., and Saadeghvaziri, M. A., "Design of through Beam Connection Detail for Circular Composite Columns", Engineering Structures, 17(3), 209-213, 1995. doi:10.1016/0141-0296(94)00002-B

2

Schneider, S.P., Alostaz, Y.M., "Experimental Behavior of Connections to Concrete-filled Steel Tubes", Journal of Constructional Steel Research, 45(3), 321-352, 1998. doi:10.1016/S0143-974X(97)00071-0

3

ABAQUS User Manual, Version 6.1, Hibbitt, Karlsson and Sorensen, Inc., 2000.

4

Lin, Ker-Chun, "Seismic Behavior of Beam-to-CFT Column Joint Using External Clamping Diaphragm", Ph. D. Dissertation, National Taiwan University, Taiwan, 2000.

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