Hybrid Fiber Reinforced Polymers (HFRP) for Strengthening Concrete Structures

Fiber Reinforced Polymer (FRP) materials have been identified as an attractive choice of materials for structural application due to their high strength, low density and good corrosion resistance. On the other hand, the mechanical behavior of FRP materials collides with the necessity to realize structural element with high level of ductility, in particular for seismic areas. Recently, many studies have been aimed to modify the constitutive law of FRP for obtaining reinforcements with high stiffness at service conditions and an adequate ductility at ultimate conditions. One of the most attractive solutions is achieved by combining different kind of fibers into the reinforcement: in particular, high modulus fibers, such as carbon fibers, and low modulus fibers, such as glass fibers, have been embedded in a polymeric resin using different volume fractions. This technique allows to obtain FRP materials with the so called hybrid effect: when the high stiffness fibers reach the ultimate strain, the load redistributes within the remaining fibers, resulting in a decrease of the elastic modulus and an increase of the ultimate strain. In this paper an experimental analysis of the mechanical properties of FRP hybrid reinforcements, is reported. Tensile tests have been carried out on different kind of hybrid FRP sheets, varying the amount of carbon and glass fibers within the composite. The experimental results, in term of stressstrain curves, have been analyzed and discussed. Finally a first application of hybrid FRP sheets to concrete elements, as externally bonded reinforcement, is presented.