Abstract：The fatigue tests of 4 kinds of high strength steel bars (i.e., HRB400, HRBF400, HRB500 and HRBF500) connected by flash butt welding were carried. For each specification of steel bars, the diameter is divided into 16mm, 20mm, 25mm and 32mm. The fatigue tests include the main high-frequency fatigue test and the supplementary low frequency fatigue tests were supplemented. The stress ratio of the fatigue tests were 0.2 and 0.4. A total of 285 specimens were tested, among which 253 specimens were effective including 212 destroyed specimens and 41 undestroyed specimens. 19 S-N curves of various specifications of high strength steel bar were obtained including 16 high frequency test S-N curves and 3 low frequency test S-N curves. The fatigue stress amplitude of 2 million times, 5 million times and 10 million times of high strength steel bars connected by flash butt welding are obtained, respectively. On the basis of the statistical analysis, the design formula for fatigue stress amplitude of high strength steel bars connected by flash butt welding is proposed, in which the effect of steel bar diameter, fatigue stress ratio and the type of high strength steel bars are considered. The research results can provide reference for the improvement of railway design codes.
