This paper presents an analysis of the numerical investigation of RC beams, strengthened with CFRP and tested in flexure, using the ANSYS © numerical analysis code. In the first part of this paper, finite-element models of RC beams (control and CFRP-strengthened), subjected to four-point bending, are developed based on experimental tests as reported in the literature. Then, a 3D nonlinear finite-element analysis (NLFEAs) with perfect bonding, along with 12 cohesive zone material (CZM) models proposed by researchers in literature, are explored to simulate the behaviour of CFRP-strengthened RC beams. In the second part of this work, the compressive strength of the concrete and the elastic modulus of the epoxy resin are examined to study their effect on the same CFRP-strengthened RC beam. On the basis of those two studies, a bilinear CZM model is modified to predict the behaviour of RC beams strengthened with FRP materials, and interfacial shear debonding phenomena. The modified CZM model is verified against a database of experimental results that includes 23 RC beams, strengthened with FRP tested in flexure, with different concrete compressive strength, FRP modulus of elasticity and resin elastic modulus. The experimental and predicted ultimate loads are compared to verify the accuracy of the modified CZM model. The level of fitness between the modified CZM model and experimental results is elaborated with statistical metrics such as integral of the absolute error (IAE), root mean square error (RMSE) and coefficient of determination (R 2 ). The results show good agreement between the experimental and predicted ultimate loads.