The increasing demand for reinforcement of concrete structures using carbon fiber composites was the main motivation of this work. This study consists of the comparison of different models that compute the contribution of the external reinforcement to the shear capacity of the beams, and of the implementation of a numerical procedure for the shear design of strengthened beams using the Brazilian code NBR 6118, the generalized truss model and the compression field theory. The objectives of this study are to supply a better knowledge of the materials used in the strengthening, to promote a better understanding of the parameters that act in the interaction between the concrete and the composite, and to systematize the design in order to obtain the carbon fiber composite cross-section area necessary for the reinforcement. The analysis of the shear reinforcement design models for determining the cross-section area of the carbon fiber composite was developed comparing the analytical results with the experimental results found in literature. The Chen and Teng model, published in 2003, for computing the contribution of the external reinforcement to the shear capacity of the beams, was used in the computational implementation due to the fact that it presented the best performance. Comparing the analytical results obtained by the theoretical model with the experimental results found in literature, the investigations showed the necessity of further studies regarding the implementation of a more appropriate model for the design of the shear reinforcement, and for a more precise computation of the cross-section area of the carbon fiber composite reinforcement.