Legame di aderenza in elementi in cemento armato confinati con armatura trasversale

The bond between concrete and reinforcement affects the ductility and the cracking characteristics of a reinforced concrete element. Splitting cracks born in the concrete around the tensile reinforced bar and they develop towards the edge of the element (splitting failure). If there is a confinement action, the concrete corbels near the ribs of the bar crash before the slitting cracks reach the edge of the element (pull-out failure). An analytical model able to evaluate the bond-slip law of confined reinforced concrete elements is developed and presented in this paper. The model is based on the studies developed by Tepfers and by den Uijl and Bigaj on the thick-walled cylinder model and extended to the case of the presence of transverse reinforcement. The bond strength and the considered failure modes (splitting or pull-out failure) are expressed as a function of the geometrical (concrete cover and transverse reinforcement) and mechanical (concrete strength) parameters of the element. The application of the proposed methodology allows to foresee the failure mode, and equations for the bond-slip law are finally proposed for a range of steel strain lower than the yielding one.