The bridged crack model has been developed for modelling the flexural behaviour of reinforced concrete beams and related size effects explaining brittle–ductile–brittle failure mode transitions. In the present paper the model is extended to analyse shear cracks, introducing a given shape for the hypothetical crack trajectory and determining the initial crack position and the load plotted against crack length curve for three-point bending problems. The proposed formulation reproduces the pure mode I flexural behaviour as a particular case, so that the flexural and the diagonal tension (shear) failure modes can be immediately compared to detect which one dominates and to determine the relevant failure load. The model can predict all the mutual transitions between the different collapse mechanisms. In the current paper these transitions are shown by varying the governing non-dimensional parameters.