Fatigue Fracture of High-Strength Concrete and Size Effect

The results of an experimental study of fatigue fracture of geometrically similar high-strength concrete specimens of very different sizes are reported and analyzed. Three-point bend notched beams were subjected to cyclic loading. The number of cycles to failure ranged from 200 to 41,000. It was found that 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 applicable 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. A linear regression plot estimating the size-adjustment parameters is derived. An LEFM (linear elastic fracture mechanics)-type calculation of the deflections under cyclic loading on the basis of the size-adjusted Paris law yields correct values for the terminal phase but grossly underpredicts the initial deflections. Overall, the results underscore the importance of considering fatigue fracture growth in the case of high-strength concrete structures subjected to large, repeated loads, and taking into account the very high brittleness under fatigue loading.