Evaluation of ductility requirements in current design guidelines for FRP strengthening

Advanced composites are widely used for the strengthening of existing concrete structures. Current design guidelines give basic requirements on how to model the enhancement of structural performance of concrete members using surface bonded FRP (fibre reinforced polymer) reinforcement. With respect to this, it is of interest to evaluate the ductility requirements which are explicitly or implicitly imposed by design guides. Based on an evaluation of four major design guidelines in Europe, Japan and North-America, and a small parametric study, the ductility aspect of the design of FRP strengthened concrete members is verified. It appears that the ductility of flexural members strengthened with FRP should be considered with care, as reduced deformability is obtained at ultimate, though generally a minimum deformability is implicitly obtained in a proper design. At the other hand, ductility enhancement by means of FRP confinement is explicitly considered in the design guidelines.