The fatigue behaviour of cracked concrete

Cracks are among the most common flaws in civil engineering structures and, considering the cyclic nature of the variable loading patterns, it is evident that the evaluation of the structure safety factor should consider the stability of cracks when fatigue loading occurs. In the present paper, the behaviour of cracked concrete subjected to cyclic loading is experimentally investigated by means of direct tension tests. In particular, the experiments concern cycles that stay below the critical concrete softening curve. The results show that, depending on the maximum load, damage could occur and that the cyclic envelope curve is very close to the monotonic quasi-static curve. On the basis of the experimental results, an empirical model for subcritical crack growth for cracked concrete under low-cycle fatigue loading is proposed.