Seismic behaviour of concrete-to-concrete interfaces subjected to combined shear and bending moment

Ductility of reinforced concrete (RC) connections is of paramount importance in seismic regions with regard to energy dissipation. Research has suggested that the presence of concrete-to-concrete interfaces subjected to combined shear and bending may reduce the ductility of RC beams under monotonic loading owing to slippage along the interfaces. In this paper, the seismic behaviour of RC beams with concrete-to-concrete interfaces is experimentally investigated by submitting specimens to cycles of reverse imposed displacements with growing amplitude. Concrete-to-concrete interfaces were located at the hogging region, to recreate a practical situation of the precast construction where continuity between precast elements is ensured by localised casting of joint connections in situ. Three types of casting interfaces were studied: (i) vertical and unreinforced, (ii) vertical and reinforced and (iii) diagonal and unreinforced. The results obtained were compared with those of a reference specimen produced without casting interfaces. Results show that the presence of casting interfaces do not reduce the specimens' maximum strength but can reduce the percentage of cycles sustained after yielding, up to failure, by 9% to 15%. Ductility, measured in terms of the ratio between ultimate and yielding displacements, was reduced by 30%. Interface reinforcement and interface direction had a negligible influence on the specimens' behaviour.