Load history dependent creep: The case of alternating creep and cyclic loading

Long-term deformations during the service life of concrete structures are predicted by creep models developed for constant loads. However, constant loads are usually superimposed by recurrent cyclic loads, for example, due to traffic. Measurements on existing reinforced and prestressed concrete bridges show that the deformations measured may be significantly higher than predicted, which is traced back to the effect of cyclic loading. Going one step further, constant creep loading and cyclic loading often occur in an alternating manner, the effect of which on the long-term deformations is more or less unknown. In the presented research, thus, the strain developments due to constant creep loading and alternating creep and cyclic loading are investigated for comparable stress levels on a normal-strength concrete C30/37. It is shown that periods of cyclic loading amplify the strain development in periods of constant creep loading and, furthermore, can significantly increase the strains. Therefore, the influence of cyclic loading on the longterm deformation behaviour of concrete needs to be considered for the improvement of existing guidelines as well as their underlying creep models.