Influence of bond-slip on the behaviour of reinforced concrete beam to column joints

The bond-slip correlation proposed by CEB is the most commonly adopted to predict slip displacements at the interface between steel bars and concrete. As known, the CEB model is based upon experimental results obtained from pull-out tests performed on bars anchored by concrete for a limited length (usually 5 d). In real beams the steel bar is usually bonded for a much longer length, and even in presence of concrete cracks, the maximum slip does not generally reach the values predicted by the CEB curve. An evidence of the above has been observed analyzing experimental data, registered during a wide campaign for testing full scale r.c. beam to column joints, carried out by the Authors. Consequently, it has been calibrated a modified bond— slip curve and an innovative test arrangement has been proposed, able to investigate bond-slip correlation for rebars in actual anchoring conditions. In the paper they are illustrated some promising preliminary results, obtained with the proposed testing setup, confirming the experimental evidence about the significant modification of the bond-slip curve with respect to the CEB one.