In order to study the reasonable value of fatigue damage factors of the railway steel bridge,based on the damage equivalent principle in European code,an iterative calculation method was proposed to determine the equivalent stress amplitudes of the traffic fatigue loading history.A calculation method of the fatigue damage factor based on completely damage equivalent was put forward.The proposed method was applied and verified with the cases of 12 kinds of standard traffic loads in European code,and the results were compared with the results of the bi-linear S-N curve calculation method.The effects of tensile-compressive stress history and the S-N curve styles on the fatigue damage factors were discussed with the proposed method.The results showed that the bi-linear S-N curve calculation method generally overestimated the fatigue damage equivalence factors and the maximum deviation was 22.5％compared with European code.The results of the proposed fatigue damage factors calculation method agreed well with the European code with the 1.1％maximum deviation.The rationality of the proposed method was verified,and the value basis of fatigue damage factor in European code was revealed.It was safe to calculate the fatigue damage factor by using the stress amplitude without distinguishing the tension-compressive stress course.The smaller the negative reciprocal m of the slope of S-N curve was,the larger the fatigue damage factor was.It was safe to calculate the fatigue damage factor with the smaller m.For the components with shorter influence line length,the calculated fatigue damage factor without considering the fatigue cut off limit was larger,which was about 1.36 times of that considering the fatigue cut off limit.When the loading length of the influence line was longer than 30 m,the influence of the fatigue cut off limit was ignorable.
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