Ductility of hybrid fiber composite reinforcement FRP for concrete

Reinforcing units of fiber composites, FRP, for concrete have elastic behavior up to tensile failure. For safety reasons a certain stress hardening and an elongation >3% at maximum load is usually required for the reinforcement. The desired behavior could be obtained with braided fiber strands around a specially made core. It is possible to increase the ductility in certain extent for braided FRP using a thin cylindrical shell core. Braids around such a core increase the ductility. Resin breaks up and a controlled collapse of the core enables the braids to rotate and compress. The optimal ratio of geometrical parameters of structure, modulus and stress state is analyzed theoretically and experimentally. The parameters are adapted so the elongation of the cable becomes ~ 3% at maximum load.