Transverse reinforcement effects on anchored deformed bars

In the present research project, long anchorages provided with transverse reinforcement were tested with the aim of studying the confining effects of the stirrups. Particular attention was devoted to gathering detailed data on bar-to-concrete slip, splitting crack propagation and stirrup stresses. To carry out the pull-out tests, a special test set-up was built, and the friction between the specimen and the reaction plate was eliminated by resorting to a sophisticated design. The results show that (a) the maximum splitting crack opening increases for decreasing transverse-reinforcement diameter size and, under service loads, reaches remarkable values; (b) anchorage capacity increases with the stirrup index of confinement Ω up to an upper bound; (c) stirrup in specimens with a small amount of transverse reinforcement yielded under service loads. A comparison with the values prescribed by building codes evidence that the bond strength prescribed by both Eurocode 2 and ACI 318-95 code remarkably underestimates the experimental anchorage capacity for large values of the stirrup index of confinement.