Aiming to develop an analytical solution to describe the behavior of reinforced concrete beams post-strengthened with FRP systems, a non-linear solution based on a tri-linear moment-curvature response was proposed. The three stages of the moment-curvature diagram are determined by concrete cracking, steel yielding and ultimate capacity of the cross section. The load-deflection responses of the post-strengthened beams are obtained by double integration of the moment-curvature curves. The analytical procedure was implemented through the Matlab® software and the numerical results perfectly agree with experimental results obtained through bending tests realized in concrete beams post-strengthened with post-tensioned and non post-tensioned FRP strips.