Strengthening the performance of reinforced concrete beams externally and internally with CFRP

Fiber reinforced polymers have become an indispensable composite material in the construction industry with their positive properties in the strengthening/repair of building elements, applying in externally or internally. These composites have properties such as high tensile strength, corrosion resistance, light weight, that will have a positive effect on the structure. This thesis consists of two series. In the first series, the aim is to investigate the effectiveness and efficiency of externally applied carbon fiber polymer (CFRP) or glass fiber polymer (GFRP) sheets/strips on the beam, considering the concrete strength, and to conduct a Finite Element Analysis (FEM) validated with it. In investigating the effectiveness, it is aimed to obtain maximum strength against optimum FRP usage. The second series aim to improve the performance of the beam by testing alternative configurations of internally applied CFRP strips according to deficiency of the beam. In the formation of alternative configurations, CFRP strips were formed to the stirrup or longitudinal reinforcement in tension zone according to the partial wrapping, full wrapping and positioning inside the beam. Within the scope of the study, 28 beams with dimensions of 200 mm (width) x 300 mm (height) x 2000 mm (length), including 14 reinforced concrete beams in each series, were subjected to four-point bending tests. Each series was divided into two groups, the first series depending on the concrete strengths (30 MPa and 35 MPa) and the second series depending on the deficiency of the beam (weak in shear and weak in bending). In order to evaluate the performance of the retrofitted beams, there are 4 control beams in total, one in each group. According to the results obtained, it was observed that the configuration applied with U-strips on the bearing areas as well as on the bottom of the beam for external strengthening contributed to a significant increase in the flexural capacity. This method also showed positive results in relatively high strength concrete. CFRP inclined strips, on the other hand, show an effective performance in increasing the shear capacity and preventing the formation of cracks. In internally reinforced beams, significant increases in bearing capacity were obtained in configurations where CFRP strips were applied to the stirrup to improve shear. An excellent strength increase was achieved in the partial wrapping where CFRP strips were applied to the side sections. However, in the configurations where CFRP strips were applied to the longitudinal reinforcement in tension zone, either no increase in bearing capacity was observed or it remained constant.