Shear strength for concrete members without stirrups is one of the most controversial aspects related to ULS. Some excellent rational models have been developed; however, most of these models were too complex to be implemented in a code of practice. As a result, most concrete codes, as the European Code 2, are based on empirical formulations. Moreover, the EC-2 procedure does not take into account the bending moment-shear force interaction. In this paper, an improvement of this procedure is presented, with the main objective of predicting this interaction. The obtaining of the new expression was based on the use of Genetic Programming techniques. Two simple expressions are obtained, being one of them able to predict the bending moment-shear force interaction. Furthermore, the two equations significantly improve the adjustment with experimental results.