Most advanced solution for strengthening of reinforced concrete structures is provided by applying high strength fibre reinforced polymers (FRPs). Two different methods are developed:
1) One of them is called Externally Bonded Reinforcement (EBR) which includes bonding of FRP strips or meshes to the surface of the member.
2) In the other case first a cut is prepared perpendicularly to the surface of the element until the first layer of reinforcement and the FRP reinforcement is glued into this cut. This is called Near Surface Mounted reinforcement (abbreviated: NSM Reinforcement).
The NSM strengthening method has a couple of advantages compared to the EBR method especially because the FRP reinforcement becomes bonded on its both sides. In this way peeling-off type failure can be avoided, therefore, the ultimate capacity of strengthening is higher.
Design and application of NSM strengthening needs further research in order to provide enough safety.
Present research will include:
(i) an experimental part with studies of parameters like length and inclination of NSM reinforcement
(ii) a modelling part with analytical and numerical studies in order to be able to describe the behaviour of strengthened elements as well as support the design process.
Application of NSM reinforcement is especially reasonable for shear strengthening of deep beams, e.g. bridge girders.
fib: „Design and use of externally bonded FRP reinforcement for concrete structures”, fib Bulletin 14, 2001, Lausanne