Experimental study on anchored bars in R.C. elements with transverse reinforcement

In the present paper, the experimental results of pull-out tests on anchorages are presented. The experiments allow for the evaluation of bar-to-concrete slip and splitting crack openings at several points along the anchored bar. Particular attention is devoted to the confining contribution of both transverse reinforcement and concrete cover. Two series of tests have been performed: in the first series, the influence of the confining contribution of transverse bars is studied, while in the second series the confining contribution of the concrete cover is analyzed. In specimens from the first series without transverse reinforcement, a splitting collapse of the anchorage occurred at the onset of the slip at the unloaded end of the anchored bar. The opposite was true for all the other specimens, as the transverse reinforcement percentage was such that a pull-out failure of the anchorage occurred. As the stirrup index of confinement Ω rose, the resultant ultimate bond stress value τ̄ increased; however, beyond the value Ωmax ≈ 0.05, there was no further significant increase of bond strength. The splitting-crack propagation rate exhibited a bilinear trend, with a faster crack propagation when the load was larger than 50% of the peak load.