Seismic loads induce local deformations at connections of H-shaped beam to concrete filled circular tubular (circular CFT) columns. Although diaphragms are used for stiffening the connections, a hole is inevitable in the diaphragms for concrete casting, and is likely to result the local deformations. The objective of this paper is to investigate the strength, deformation capacity, and failure modes of connections of steel beams to circular CFT columns by testing simple tension specimens. Furthermore, a FEM model is developed to predict the elastic-plastic behavior of the connections with various dimensions and material properties.
Seismic loads can induce shear in the panel zone and local tensile deformation of a connection between H-shaped steel beams and concrete filled circular tubular (circular CFT) columns. In this paper, the focus is on the local deformation of a connection. However, the diaphragm does not have a perfect stiffening effect, because it must have a substantial hole to allow the column tube to be filled with concrete. The local deformation of a connection leads to the reduction of the rigidity and strength of a whole building frame. On the other hand, it may be expected that the local deformation reduces the beam flange strains, and consequently early fracture of the beam flange is well prevented. Therefore, the local deformation should be controlled by adjusting the diaphragm dimensions, in order to realize the optimum condition of the seismicresistant capacity of a building frame. Four connection types are popularly adopted in beam-to-column connections for circular CFT columns:
the connection with polygon-shaped, external diaphragms;
the connection with circularshaped, external diaphragms;
the connection with internal diaphragms with center circular holes and extended flanges (the cutthrough diaphragms); and
the connection without any diaphragm (non-diaphragm type) [Fig. 1].
