Different resisting actions interact in the shear resistance of cracked concrete beams whose relative importance varies along loading as damage evolves. Thus, it is not possible to establish a governing resisting action in a general sense. Yet, most formulations for shear design models are empirically or semi-empirically based, which generally focus on one principal action, and show large scatter. Nevertheless, recent numerical models can complement experimental investigation, contributing to improve knowledge of the phenomenon and its state-dependency. In this paper, a mechanical model for the prediction of the shear-flexural strength of reinforced (RC) and prestressed (PC) concrete members with or without transversal reinforcement is presented. The model explicitly consider the different contribution of each shear resistance actions and is suitable for rectangular, I- or T-sections. The model is derived combining continuum and fracture mechanics and after setting a set of plausible hypotheses based on experimental and numerical observations at the limit stage of imminent shear failure, which allowed for simple equations suitable for design and assessment. The validation of the formulation is carried out by comparison against an extensive database of more than 1200 tests on RC and PC beams with and without stirrups with small bias and scatter.