In this paper an analytical method is derived for high-strength reinforced concrete beams (HSRC) retrofitted with fiber-reinforced polymer (FRP) plates to determine the allowable plate area and achieve a targeted value of ductility. The proposed method provides designers with a useful tool for designing levels of ductility. Nonlinear models for concrete and reinforcement are applied. The evaluation of ductility is based on a concrete model that doesn't consider concrete confinement effects. The derivation of equilibrium and compatibility equations for a rectangular cross section is presented, and the solution to the nonlinear equation for determining the allowable plate area is demonstrated with example. Analytical results are compared with experimental data reported in literature. It is noted that additional conditions need to be checked to ensure ductile performance, such as local failure of the concrete layer between tension reinforcement and FRP plate or debonding of the plate itself.
