Stiffness and ductility of fibre-reinforced polymer-strengthened reinforced concrete members

The use of fibre-reinforced polymer (FRP) composites for repair and strengthening of civil engineering structures is gaining increasing acceptance worldwide and can be considered close to achieving the status of mainstream technology. Especially widespread is the application of externally bonded FRP laminates and bars for flexural strengthening of reinforced concrete (RC) members. Although a vast amount of experimental and theoretical research has been devoted to quantifying the strength of FRP-strengthened beams, less attention has been paid to stiffness and ductility aspects. The aim of this work is to carry out a systematic numerical analysis of the influence of the most relevant parameters on stiffness and ductility of FRP-strengthened RC cross-sections. As far as stiffness is concerned, the substantial advantages related to the use of active (i.e. pre- or post-tensioned) strengthening systems are quantified. For evaluation of ductility, an energy-based index is proposed which allows comparison of cross-sections with different amounts and types of FRP reinforcement accounting implicitly for their different moment–curvature behaviour. The damage accumulation of the cross-section is also addressed by means of an energy-based index and of the Park–Ang damage index.