In order to analyze the influences of different stiffeners on joint performances in extended end plate connections, the finite element method with large and elasto-plastic deformation, suited to contact problems, was used. Effects of the size of extended end-plates and backing plates for column flange on rotational stiffness and resistance of the beam to column connection are studied. Developments of end-plate deformation and departure from each other between end plate and column flange were studied. It is found that the equilateral triangular stiffener with the beam web thickness will yield and/or buckle prematurely. When the stiffener angle is 63.4°, it can increase arm length against bending of the connection, thus reducing bolt tensile force, delaying the local buckling of beam compressive flange and forcing the beam plastic hinge to the end of the stiffeners, therefore such stiffeners enhance strength and stiffness of the connection significantly.
