Variable shear span-depth ratios for reinforced concrete beams strengthened with various carbon fiber-reinforced polymer configurations

This paper presents an experimental study on the behavior of reinforced concrete beams strengthened with externally bonded (EB) carbon fiber-reinforced polymer (CFRP) sheets or near-surfacemounted (NSM) CFRP strips. A total of nine beams are monotonically loaded in flexure until failure occurs to examine the effect of variable shear span-depth ratios (a/d) ranging from 2.5 to 5.5. The effect of a/d is apparent on the load-displacement behavior of the test beams in terms of load-carrying capacity and deformability. Stress redistribution is observed for the strengthened beams prior to the occurrence of CFRP-debonding failure. The mode of failure is controlled by the degree of a/d in such a manner that: 1) the EB beams demonstrate shear-compression failure at a/d of 2.5 and 4.0 and shear-tension failure at an a/d of 5.5; and 2) the NSM beams reveal shear-crack-induced CFRP-debonding at a/d of 2.5 and 4.0, whereas the NSM beam does not show any evidence of debonding at an a/d of 5.5. The NSM beams dissipate more energy than the EB beams because of enhanced bond. The local rotation of the strengthened beams is restricted by the presence of the CFRP. As an a/d ratio increases, the bias factors (a ratio between test and prediction) of the experimental beams tend to augment. The moment-shear interaction of the strengthened beams is evaluated against theoretical equations. It is recommended that the effect of an a/d ratio be taken into account when CFRP-strengthening is designed.