The plastic deformation capacity of steel beams is regulated as restriction on the depth-thickness ratio by the Japanese building design codes. The capacity is, however, determined not only by the depth-thickness ratio but also by the collapse mode of the beams. Controlling the collapse mode improves the plastic deformation capacity of the beams. In this paper, difference in plastic deformation capacity and collapse mode is evaluated by the ratio of the shear strength to bending strength of beams and an example of rational design of steel beams is introduced.
