This research aims towards presenting an appropriate model for analyzing reinforced concrete (RC) beams repaired and strengthened using jackets of cementitious materials. The jackets incorporated chemically activated fly ash with glass fiber to enhance the load carrying capacity, cracking load and ductility at normal temperature and after exposed to elevated temperature. Three-dimensional nonlinear finite element (FE) model has been developed using finite element package, ANSYS 14.0. Eleven RC beams strengthened using plain or RC jackets containing activated fly ash and glass fibers and loaded with four-point loading arrangement were analyzed. The parameters of the study comprised damage level induced before jacketing, effect of exposure to elevated temperature and effect of jacket reinforcement. The finite element results obtained in this investigation; ultimate flexural capacity, mid-span deflection, crack progression, failure mode and stresses in concrete, showed good agreement when compared with the available experimental data results. The presented FE models showed the potential of performing numerical simulation instead of experimental tests to save time and costs.