Open issues in design procedures for FRP strengthening of reinforced concrete bridges

Several materials and methods are available for strengthening RC bridges. In particular, exter- nally bonded FRP sheets/plates have found increasingly wide applications in bridge engineering. The struc- tural behaviour of FRP-strengthened RC structures has been widely studied over the last decades but, despite the number of works available in literature, design procedures aimed at checking the efficiency of the strengthening technique are not well defined yet. In particular the efficiency of the intervention in relation to the characteristics of the existing RC structural element, particularly the existing steel reinforcement, does not seem deeply studied. Particular problems/critical issues related to bond between concrete and FRP, shear strengthening, confinement of columns are topics currently under investigation by the scientific community and code predictions related to these problems can lead to unconservative results. This work has the aim to point out these general problems/critical issues on the basis of the actual experiences.