Numerical investigations on the flexural behaviour of RC beams retrofitted with FRP

The rehabilitation of the reinforced concrete structures is an important problem in civil engineering. The wide use of fiber reinforced polymers has outlined the need of research to study this application in civil structures. Consequently, the research world has tried to find the more appropriate an-swers. Due to their useful properties, Fibre Reinforced Polymer (FRP) are finding ever-increasing use for restor-ing and repair. Nevertheless, in spite of the increasing number of applications of this strengthening technique, the complexity of the mechanism at FRP-concrete interface influences the local phenomena which have to be under-stood and correctly predicted in order to obtain a reliable evaluation of safety margins of rehabilitation design with respect to both ultimate and service-ability limit states. FRP plates or sheets externally bonded are one of the most efficient techniques for externally bonded reinforcement (EBR) of rein-forced concrete (RC) elements or of the existing structures. In literature, some studies concerning these local phenomena can be found. The first ap-proaches were based on linear-elastic assumptions, but research is still in progress and takes into account also the non linear behaviour of the prob-lem. The research presented in this pa-per is aimed at describing the local phenomena which affect the behavior of the EBR-RC beams tested in bend-ing. To localize the study, some small specimens have been previously inves-tigated. The study presented in this paper is performed by theoretical and numeri-cal analysis on both some specimens with simple geometry and on some RC beams. The theoretical model, based on the concepts of Fracture Mechanics, is aimed at evaluating the stiffness of both integer and cracked element and at correlating the actual behaviour of the specimen with different parameters (crack’s height and kind of FRP). Fi-nally, a numerical analysis has been performed using Matlab 5.1. The frac-ture energy has been evaluated and the parametric investigation on different values of Young’s modulus of FRP al-lows to outline the influence of FRP on a cracked section.