Fire resistance of beam-to-column fully welded connection joint in steel frame

Abstract

Full-scale fire tests were conducted on fully welded connection joints in steel frames (FWC-SF) to investigate the effects of load ratio and fireproof coating on the fire resistance, critical temperature, and failure modes. Three specimens were tested, the temperature distributions and deformation responses under fire exposure were obtained. The results indicated that the heating rates of FWC-SF joint components varied, while fireproof coating could mitigate these differentials. Local buckling of the highly heated steel beam bottom flange and web was identified as the fundamental cause of joint failure, with the beam load ratio being the dominant factor affecting fire resistance. Finite element (FE) models were developed and reproduced the temperature field and fire performance of FWC-SF joints as recorded. A series of parametric studies was performed, revealing a threshold effect of column load ratio on fire resistance, and acquiring reduction factors for the initial rotational stiffness and ultimate bending moment of the FWC-SF joint at elevated temperatures. At 600 °C, the ultimate moment decreases by about 50 %, while the initial rotational stiffness is reduced to 15 %, and the FWC-SF joints nearly lose rotational stiffness above 700 °C.