The objective of this work is to contribute to a better understanding of the shear behavior of reinforced concrete beams without and with steel fibers via their resistant mechanisms. For this, a comprehensive review of the state of the art was made and, based on this review, the experimental study carried out was planned. This study contemplated four concrete compositions that aimed a concrete compressive strength around 40MPa, varying the volume content (Vf = 0.0 percent, 0.5 percent or 1.0 percent) and the aspect ratio of the fibers (lf /df = 45 or 80). In addition to the materials characterization tests, tests were carried out to study the dowel action and the aggregate interlock effects and also tests of beams without stirrups with span to effective depth ratio of 2.55. Influence of Vf(lf/df) in the dowel action and the aggregate interlock effects, as well as in the behavior of the beams was observed. The use of Digital Image Correlation (DIC) allowed monitoring the cracking of the tested specimens and to obtain information that led to theoretical models to analyze the dowel action and the aggregate interlock effects. The obtained photogrammetry data during the beams tests made it possible to follow the formation and kinematics of the critical diagonal crack and, based on these data and on the models proposed here and on others presented in the literature, the contribution of the resistant mechanisms in different loading stages was analyzed. It was possible to observe that similar beams may present differentiated position, shape and kinematics of the critical diagonal crack, although with similar global responses. As a result, the contributions of the resistant mechanisms are also different.