Fatigue fracture of high-strength concrete and size effect

Results of an experimental study of fatigue fracture og geometrically similar high-strength concrete specimens of very different sizes are reported and analyszed. Three-point bend notched beams 1.5, 4.24, and 12 in deep were subjected to cyclic loading with a lower load limit of 0.07P_u and an upper limit between 0. 73 and 0.84 P_u. It is found that the Paris law for the crack length increment per cycle as a function of the stress intensity factor, which was previously verified for normal concrete, is also appicable to high-strength concrete. However, for specimens of different sizes, an adjustment for the size effect needs to be introduced, of a similar type as previously introduced for normal concrete.