The present study tested the shear strengths of four reinforced concrete composite beams, simply supported and with two point loads. Each beam had a different treatment of the interface between the two concretes casted at different times in order to resist the horizontal shear at the interfaces: smooth surface or very rough surface, with or without additional shear connectors. Some parameters were fixed, such as the length and geometry of cross sections, longitudinal reinforcement ratios, shear reinforcement ratios and shear span-depth ratios of specimens. The nominal compressive strength of concretes (30 MPa) was the same for the two concretes used in the composite beams and for all the specimens. The aim of these tests was to analyse the influence of horizontal shear on the behaviour of reinforced concrete composite beams subjected to vertical shear stresses. This communication shows the results of these tests, in particular: the horizontal shear stresses and loads and shear forces reached during the tests, comparing them with those calculated according to design codes fib MC, EC2 and ACI 318. While horizontal shear failure was expected in three of the beams, they all failed due to vertical shear, which was also theoretically underestimated. It was observed that an interface existing between two concretes casted at different times influences the shear strength mechanism developed by the structural element and, therefore, the reached strength.
García et al. (Wed,) studied this question.
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