This paper describes the plastic deformation capacity of beams which are fabricated from high strength steel with low yield ratio, or high yield ratio. And collapse forms of beams with stocky flange plate are shown by experiments and numerical analysis. These collapse forms are the lateral buckling and the ductile fracture of the tensile flange. The deformation behavior of beams is not influenced by the yield ratio when beams are collapsed by the lateral buckling. Finally, the plastic deformation capacity of considering the ductile fracture of the tensile flange is shown by the flange width-thickness ratio and the moment gradient.
