Fatigue strength of rebars embedded in concrete-A numerical approach

The effect of embedding in concrete on the fatigue performance of steel reinforcement bars is not evident. Some test series provided in literature demonstrate a higher fatigue resistance of embedded bars as compared to bars in air, whereas others provide a lower resistance. In addition, debate exists on the mechanisms behind the difference between tests in air and tests in concrete, if any. These mechanisms mentioned in literature are empirically based. This paper provides a numerical (finite element) study on the stress concentration factors and the stress intensity factors for the two conditions. It shows that the locations of cracks in concrete relative to the ribs on rebars and the distance between concrete cracks have little influence on the stress peaks in the rebar and hence on the fatigue performance of the rebar. Mechanical interlock or pressure of concrete against the ribs slightly contributes to the rebar stress concentrations. No significant difference should be expected in fatigue resistance between rebars in air and rebars embedded in concrete. Variations in local geometry at the root of ribs appear of more significant influence.

Automated summary

This study indicates that embedding steel reinforcement bars in concrete does not significantly improve fatigue performance compared to bars in air. Factors such as crack location, distance between concrete cracks, and mechanical interlock have little impact on rebar stress peaks and therefore on rebar fatigue performance. No significant difference in fatigue resistance should be expected between rebars in air and rebars embedded in concrete. Variations in local geometry appear to have a more significant influence on fatigue performance.