Strain-based analysis of reinforced concrete pull-out tests under monotonic and repeated loading

Abstract

This paper presents the results of an experimental campaign on standard pull-out specimens instrumented with refined strain measurement techniques. The quasi-continuous strain measurements allowed the derivation of experimentally substantiated local bond stress-slip relationships for static and repeated loading. It was shown that the force transfer between concrete and reinforcement along the bond length is not uniform and that redistribution occurs with increasing as well as repeated load. The variation of bond stresses along the bond length is of great importance for fatigue studies, as the fatigue damage depends on the level of the applied stress. In addition, the refined measurements revealed non-uniformities in the unloading behaviour. Thus, a slip reversal occurs mainly on the loaded side of the pull-out specimen. The experiments confirmed that the residual nominal bond strength after repeated loading does not significantly vary from the initial bond strength, and the redistribution capacity was identified as a possible cause. The comparison with the nominal bond-slip relationship obtained in a conventional test setup agreed well with the mean value of the refined measurements. However, local degradation processes, such as fatigue, cannot be investigated properly with conventional pull-out tests.