To obtain the fire resistance of beam-to-column semi-rigid joints for CFST frames

a numerical analysis of the thermal mechanical coupling behavior of extended end plate joints between CFST columns and steel beams in fire was done.The constitutive models of steel and core concrete material at high temperature were determined.The nonlinear finite element modeling of extended end plate joints to CFST columns was made considering the floor effect.The full process analysis of the typed connections under three-face fire and loading was carried out.The effects of load ratio

bolt pretightening force

fire protection layer thickness and material properties

geometry dimension of the main parameters on the fire resistance of the joints were studied.The research results show that the load ratio

the bolt pretightening force

the fire protection layer thickness and the dimensions of the steel beam significantly affect the fire resistance of composite joints.It provides the scientific basis of the design theory of semi-rigid CFST frames in fire.