Verification on both load-bearing and plastic deformation capacity for a steel beam-column welded connection at elevated temperature is of importance to secure fire safety of steel building structures. At the fire resistant design, it is required that the beam-column welded connection does not fracture before the adjacent heated steel beam exhibits stable plastic collapse mechanism. The AIJ design recommendation (Architectural Institute of Japan, 2017) cannot, however, offer a fire resistant verification method for the beam-column welded connection, because the fire resistance has not been verified experimentally. Main purpose of this study is to clarify both load-bearing and deformation capacity for steel beams including the beam-column welded connections at high temperature, by conducting their experiments under a condition on constant temperature and gradually increasing load.
The beam-column welded connection with through diagrams is arranged in the center of beam specimen. The boundary condition is simple support and a shear force is applied through the medium of the column above the beam-column welded connection. In the welded connection, scallop working for a web plate in the wide flange section is not used. This kind non-scallop working is widely used for the actual beam-column welded connections to avoid brittle fracture at the structural design in Japan. The base metal and weld material are JIS SN490B and JIS YGW11, respectively. Stiffener plates to avoid local buckling of the flange plate in the beam are arranged near the beam-column welded connection, because the large tensile force is acted to the welded connection. The number of specimens is five and an experimental parameter is specimen temperature, which is given by ambient temperature, 600, 700, 800 and 900 °C. The specimen temperature was gradually risen by an electric furnace, and the shear force was applied after the temperature reached to the test temperature and kept constant it. Bending moment and rotation angle of the specimen are estimated respectively, and the shear force loading continued until the rotation angle exceeded 0.2. From minute investigations on the experimental results, the following knowledge was obtained.
All specimens exhibited the beam bending collapse mode and the welded connections did not fracture. They possessed the larger bending strength than the full plastic moment at each temperature. The shear force applied at the high temperature experiments approximately kept constant with the specimen plastic deflection increase. From specimen observation after those experiments, the weld metal itself in the beam-column connection besides the beam largely deformed, however, ductile cracks in the weld metal and heat affected zone were not observed. It is expected that the beam-column welded connection with the high seismic performance by the non-scallop working also possesses the high load-bearing and deformation capacity at the fire. Furthermore, in-plane numerical analyses using a beam element were conducted, and it was clarified that both numerical and experimental specimen behaviors approximately agreed.
