Mechanics of bond under repeated loading

In the last two decades, an increase in the live loads applied to structures, such as bridges, coupled with a decrease in dead load due to the use of lighter high-strength materials have made the effect of repeated loading on these structures more pronounced. The concrete–steel bond dictates the behaviour of reinforced concrete at the serviceability and ultimate limit states. However, relatively little research has been reported in the literature studying the effect of repeated loading on bond. In this study, nine reinforced concrete anchorage-beam specimens (250 × 150 × 2000 mm) were tested under different repeated loading range levels. The results showed that bond fatigue failure could occur for load ranges as low as 45% of the beam’s static capacity and that the load-life behaviour was linear on a log–log scale. As the number of cycles increased, the slip behaviour changed from a stable to an exponential increase. This was accompanied by a redistribution of the bond stress along the bonded length. Based on the experimental observations and data analysis a description of the mechanics of bond stress and slip under repeated loading is presented.