continuous and butt-welded specimens of different types of british high-yield reinforcing bars have been fatigue tested, in air, at endurances up to 10 8 cycles. a mean line relationship between stress range (sigma r) and cycles to failure (n) of n sigma r 9.5 = 1.8 x 10 29 has been derived for continuous bars and it is suggested that the inclusion of high-yield reinforcement in the code of practice for fatigue for the design of bridges (bs 5400 part 10) will necessitate the introduction of a class r design curve. the results for welded bars were in general agreement with the class d design curve of bs 5400 up to endurances of approximately 2 x 10 6 cycles. as endurance increased beyond this value, the d classification gave increasingly conservative estimates of permissible stress range. the effect of bar diameter on fatigue performance was briefly examined and it was found that large bars were significantly less resistant to fatigue damage than smaller bars of the same type. the fracture surfaces of a representative selection of specimens have been examined by scanning electron microscopy to investigate the effect of surface features of a bar on its fatigue performance. it was found that the fatigue cracks in continuous bars had initiated at small defects associated with the surface oxide layer and that the rib pattern on deformed bars had little influence on the positioning of the crack initiation sites.(a)

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