The effect of concrete strength on the behavior of sheetbeams reinforced with different CFRP types

In this study, the changing behavior of reinforced concrete beams manufactured in 5 different concrete classes with insufficient shear capacity, under equilibrium, under vertical load, as a result of regional reinforcement with CFRP in shear openings, was investigated experimentally. In the study, the behavior of CFRP, which will bring the beam behavior to the ideal level in terms of strength, strength and ductility, according to the norms in the regulations, was observed according to the weight and three types of wrapping. In the experimental study, 35 pieces of 1/3 scale reinforced concrete beam samples of 100x150x1000 mm were prepared. The longitudinal reinforcements in the beams are 2Φ8 and 2Φ10, while the stirrups are chosen as Φ6/50 mm, two each on the supports only and five in the middle span region, in order to have insufficient shear capacity. It has been observed that the CFRP used in the study can enable the beams to reach their bending capacity rather than shear failure, or that the concrete experiences sudden ruptures with cracking. In the Turkish Building Earthquake Code (2018) only the full wrap type is included in the reinforcement of beams against shear, and reinforcement of the beam from two or three sides in ACI 440.2R-17 (2017) (Design and Construction Guide of Externally Bonded FRP Systems for Reinforcement of Concrete Structures). For this purpose, the external characteristic compressive strength of concrete must be at least 17 MPa and the characteristic concrete tensile strength must be at least 1.4 MPa. In this study, it was observed that full wrapping was more effective on the strength and behavior of the beam than wrapping on two and three sides, especially for concrete strengths of 5 20 MPa. It is thought that detailed information about the concrete class of the structural elements to be strengthened and the weight of CFRP in the regulations will bring more appropriate and more economical solutions. Keywords: carbon fiber material (cfrp), cutting, bending, reinforcement, reinforced concrete beam, concrete grade, wrap type