Determination of optimum frp composite amount in strengthening reinforced concrete beams with inadequate shear strength

In this study, the behavior of the reinforced concrete beams having insufficient shear capacity under vertical loads was experimentally examined and the optimum strip width (wf) / strip spacing (sf) ratio of the CFRP, which will bring the behavior to the ideal level according to the code norms, was determined as a result of the strengthening of the beams with CFRP. In the experimental study, 8 samples of 125 x 250 x 2500 mm reinforced concrete beams with ½ scaled were prepared. In order to have insufficient shear capacity in the beams, stirrups were chosen as Ø5 / 35 cm. The other specimens were tested at increasing CFRP (wf) / (sf) ratios along the shear span, while one of the samples was tested as reference without strengthening. According to the experimental results, when the (wf) / (sf) ratio exceeds 0.55, the brittle behavior changes as ductile behavior. However, it is also seen that (wf) / (sf) ratio should be increased up to 0.82 in order for the beam to reach sufficient shear capacity according to the code norms. It was observed that the direction and unit weight for per square meter of the CFRP used in the study was one of the most important factors in strengthening and especially the 240 gr / m2 CFRP experienced sudden ruptures in the shear areas together with the shear cracks of the concrete.