Experimental Study On Circular Fillet Diaphragm-through Joint

In frame structures with concrete-filled square steel tubular members, diaphragm-through joint has been regard as recommended type in technical specification of our country. However, because studies on diaphragm-through joints are very limited, calculating theory and design method are not well developed in the corresponding codes and regulations, which restrict its practice in the project.To coordinate the promotion of concrete-filled square steel tubular column structure and the implementation of new design code, this paper summarizes joint types of moment resisting connections between concrete-filled square steel tubular column and steel beam, and simply introduces the present research of rigid joints. On the basis of above investigation, experimental study on cicrcular fillet diaphragm-through joints is carried out to understand its mechanical property.Based on the tensile load-bearing capability theory of diaphragm-through joint presented in specification of Japan, eleven specimens of the joint model are studied by static tensile test to investigate the structure behavior of the connection between concrete-filled square steel tubular column and steel beam flange. The failure process and feature of each specimen are described and the stress transfer mechanism in the connection zone is analyzed. Then comparing analysis is executed on the measured value and the calculated value of bearing capacity of this joint. Research results suggest that cicrcular fillet diaphragm-through joint model has high capacity and good ductility and that the yield capacity and stiffness can be increased by the concrete filled in the tube. Load-bearing capability calculated from the theoretical formula is conservative for the specimens with the tube filled in concrete, but overly estimates the strength of the specimens without concrete.In order to study the seismic performance of diaphragm-through joint, four full-scale cruciform specimens are studied under quasi-static test. The failure process and feature of each specimen are described. Based on the measured hysteresis loops, this paper makes a thorough comparing analysis on the index of seismic behavior such as load-carrying capacity of the joint, ductility, energy dissipation, and rigidity degeneration. The analysis results show specimens of diaphragm-through joint have good ductility and enough energy dissipation capacity. Details of the steel beam flange with the diaphragm have obvious effect on the ductility, energy dissipation and rigidity degeneration, and the seismic performance of joint of circular fillet type are better than those reinforced by taper plate welded to the beam flanges and diaphragm.