Acta Scientiarum Polonorum

In the paper, the fatigue strength of ribbed reinforcing bars, not embedded in concrete, with the diameter of 32 mm, made of the B500SP steel grade for pulsating tensile stress, has been determined. The fatigue tests were performed on the Instron 8806 machine under axial tensile loading. Each of the fatigue tests was run until damage or up to 2·106 cycles of loading. The fatigue tests were performed on 12 specimens. The specimens were cut from one bar of the length 12 m. The fatigue strength of the steel being tested was determined by the classical method consisting in making of a Wöhler curve (S – log N curve). The determined fatigue strength Zrj = 135 MPa for 2·106 cycles constitutes ca. 22% of the tensile strength and also is much lower than the yield point (it is ca. 26% of its value). The paper identifies the factors that may affect the value of the fatigue strength.