Abstract Evaluating the cumulative damage of seismic members is an important issue in seismic design. Steel beams are the primary components of seismic moment-resisting frames, wherein the story drift angle and ductility factor with respect to the number of cycles are used as indices of the degree of damage. The former is widely used in the United States and several other countries, whereas the latter is used in Japan. Additionally, these indices are used to express the plastic deformation capacity up to the ultimate state determined by fracture or other failure modes. In this study, an appropriate evaluation method was developed based on the numerical analysis of sub-assemblies for determining the cumulative damage and plastic deformation capacity of steel beams. The analytical results indicate that a unified evaluation is possible based on the relationship between the ductility factor of the beam of each steel grade and the number of cycles to fracture. The proposed method can be used regardless of geometric conditions, except in the case of short-span beams.
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