Research on Ultimate Strengths and Elasto-Plastic Behaviors of Beam-to-Square Tube Column Connections with 4-plate External Diaphragms

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The purpose of this research is to obtain the ultimate strengths and elasto-plastic behaviors of H-shaped beams-to-square tube column connections of 4-plate external diaphragms in comparison with those of ordinary diaphragms. The types of diaphragms used in the experiments are two types of proposed diaphragms for internal and external columns in a building, and the ordinary external diaphragm type. Other experimental parameters are ultimate strengths of filled concrete (Fc=210kg/cm^2, and 450kg/cm^2) and axial forces (N=0.3Ny). The specimens were subjected to an axial load, and the lateral loading was simulated by applying verical loads to the beam ends simultaneously.All of the specimens of 4-plate external diaphragms displayd ductile response as well as those of the ordinary diaghragms did. The failure mechanisms of the specimens were classified to four groups, such as shear buckling of connection panels, local buckling of column plates, local buckling of beam flanges and fracture of beam flanges. The 4-plate external diaphragms were broken in spite of severe stress concentration. The ultimate strengths of 4-plate diaphragms were almost equivalent to the calculated values which were obtaied through the previous experiments. Consequently, the ultimate strength of a beam-column connection with 4-plate diaphragms can be estimated by the proposed equations. The deformability of the specimens of 4-plate external diaphragms were not inferior to those of the ordinary external diaphragms. However, the deformability of the specimens of high strength concrete was inferior to that of the specimens of ordinary strength concrete.