Abstract: In order to reveal the effects of the thicknesses of end-plate and stiffener on the failure modes of extended end-plate connection in a fire,the formation conditions of one or two groups of plastic hinges in the tension zone of end-plates were investigated based on the elastic-plastic theory and validated by using nonlinear FEM(finite element method).The research result shows that with the increase of temperature,two groups of plastic hinges will be formed in the tension zone of an end-plate with a thin thickness,and large plastic bending deformation occurs to lead to a large rotation of the beam and severe local buckling of its bottom flange in compression.Under the condition of a thin stiffener and a thick end-plate,only one group of plastic hinges will be formed,and stiffener buckling will result in the failure of the connection.The conditions to form the plastic hinges in the connection in a fire are nearly the same as those at room temperature,but the most common failure mode in a fire is severe local buckling.Therefore,the thicknesses of end-plate and stiffener should be increased properly to avoid the buckling of stiffener and beam flange and improve the fire resistance of the connection significantly.