Effectiveness of applying FRP-strengthening to enhance the seismic performance of a RC frame structure is studied in this paper. The performance is expressed in term of reliability which implies calculation of the probability to reach the required level of performance under specified loadings and environmental conditions. The proposed approach was applied to a typical three-storey RC frame structure. Two strengthening configurations are compared: applying flexural FRP-strengthening to members – beams/columns – and/or applying FRP-confinement to columns of the structure. Seismic reliability assessments are presented in term of fragility estimates which involves performing nonlinear time history analysis to record the maximum lateral top drift of the RC frame structure under seismic loadings. This analysis is carried out using finite elements method. To reduce the computational effort, an efficient meta-modelling method based on Polynomial Dimensional Decomposition PDD in conjunction with the Monte-Carlo Simulation is developed. Results of simulations demonstrate the efficiency and computational advantages of the proposed method for the seismic reliability assessment of RC frame structures. Furthermore, the results confirm a significant increase in reliability of RC-frames subjected to seismic due to FRP-flexural/FRP-confinement strengthening especially in case of applying FRP-flexural strengthening.