This paper presents the improvement of the EC-2 shear strength formulation for concrete beams without
shear reinforcement. The method used is based on the modification of the Genetic Programming (GP)
technique configured to generate symbolic regression from a set of experimental data. Starting from
the EC-2 formulation, several points of the equation are subject to optimization, together with the set
of restrictions that must be fulfilled, achieving in this way to control and direct the searching process.
It is specifically pursued to improve the term of size effect, the influence of the amount longitudinal
reinforcement and the bending-moment–shear-force interaction. For the development and checking of
the models it has been used in about 1200 experimental tests on concrete beams from the literature.
The four expressions obtained are analyzed in depth through GP and, finally, three expressions of great
simplicity are proposed that improve, significantly, the shear strength prediction with respect to the
proposals of the Eurocode 2 and ACI 318-05 Code.