Abstract: The concept of Equivalent Nominal Stress (ENS), relationship between a structural Detail Fatigue Rating (DFR) and Fatigue Stress Concentration Factor (Kf) and the determination method of the structural DFR under variable amplitudes are presented. The ENS and the relationship between DFR and Kf are very important for structure fatigue analysis. When some structural ENS and locations come up to plastic condition, the ENS and the above relationship must be used to determine DFR under variable amplitudes. The tests and analytic examples show that the method presented in this paper is correct.

Key words: equivalent nominal stress, structural DFR, variable amplitude