A Study on Connection Strength and Deformation Capacity of H-Shaped Steel Beams to Concrete Filled Circular Tubular Columns

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Although diaphragms are used for stiffening the connections of H-shaped beam to concrete filled circular tubular (circular CFT) columns, a hole is inevitable in the diaphragms for concrete casting, and is likely to result the local deformations. Therefore, a prediction of the deformations will be required in the seismic-resistant design for the connections.At the first research year, the strength and the deformation capacity were investigated by testing simple tension specimens, each of which was composed of a stub column, beam flanges, and a diaphragm. One of the test parameters was the connection type, i.e. a connection with an external diaphragm of polygon-shape or circular-shape, a connection with a cut-through diaphragm, and a non-diaphragm connection. The test revealed that connection failure modes were the punching shear cracks in a column tubular wall and/or the ductile fracture of a diaphragm plate. Since the large plastic elongation occurs prior to the failure, the deformation capacity may be enough, if the connection is stiffened by diaphragm plates.At the final research year, cruci-form frame specimens were tested. The specimen was subjected to a constant axial load and repeated beam-end loads as seismic loads. Differing from the simple tension specimen, the punching shear crack of column tubular wall was only the mode of failure. The reason may be the load repeating, which accelerates the strain concentration on tubular walls. However, the deformation capacity may be enough.A finite element model of connection (FEM model) is developed. The accuracy of the FEM model was demonstrated by a comparison with the test results. In the future, by performing a parametric analysis of the model, the authors will construct a numerical database and develop a prediction method of the local deformations of connections.