Non linear analysis of r.c. beams strengthened with frp: theoretical-numerical comparison

The adoption of innovative, advanced materials such as fiber reinforced polymer composites (FRP) has encountered a great growth in these last years, particularly for the Civil Engineering, in the strengthening field. These materials, made of carbon, glass or aramid fibers bonded with a polymeric matrix, are generally externally applied to existing elements. The FRP properties (high strength and stiffness in the fiber direction, immunity to corrosion, low weight) and the ease of installation have led this new technique to compete with traditional ones. All these positive aspects have given a new impulse to the study of the behaviour of strengthened elements. The FRP possibility of providing strength increases to r.c. and masonry structures is well known and recognised, but many uncertainties are still related to the ductile behaviour of r.c. structures reinforced with FRP composites. A first analysis of the influence of the FRP sheets on the local ductility of r.c. beams has been carried out by some of the authors in previous papers. A simple analytical model, able to account for non-linear behaviour of materials, strain localization and tension stiffening effects, was developed. The obtained results, expressed in terms of strength and ductility by means of interaction domains, have confirmed the effectiveness of the intervention in increasing the bearing capacity, but also a reduction of the plastic strain spreading. These remarkable aspects will be deepened in this paper by means of a comparison among numerical analytical and experimental outcomes.