ABSTRACT
Abstract Reinforcing units, FRP, of mono fiber composites for concrete have elastic behavior up to tensile failure. For safety reasons an elongation > 3% at maximum load is usually required for the reinforcement. The ductile behavior with the necessary elongation and stress hardening could be obtained with unidirectional hybrid fiber composite when ductility is caused by multiple breaking of low elongation fibers before total failure of composite. However too good bond between the fibers and matrix results in dynamic crack spreading from failing stiff fiber bundles to those with lover modulus. Another possibility to increase ductility of FRP consist in use of braided fiber strands around a soft porous core: in this case ductility increases when epoxy resin breaks up and collapse of core enables the braids to rotate. Keywords: Fiber composite reinforcement, FRP, ductility, hybrid fibers, braids, porous core, concrete.
