Reinforced Concrete Beams Retrofitted with External CFRP Strips towards Enhancing the Shear Capacity

The practical difficulties in upgrading the structural performance of existing reinforced concrete (RC) structures is discussed, when retrofitting structural members by conventional RC jacketing. The use of retrofitting schemes employing externally applied fiber reinforcing polymer (FRP) strips attracted considerable research attention as a preferable alternative. Such retrofitting FRP schemes aiming to upgrade the shear capacity of existing RC beams have been examined in many published works employing such externally applied FRP shear reinforcing schemes without confronting the practical difficulties arising from the presence of the RC slab. Anchoring external CFRP strips aiming to shear upgrade, which is the focus here, overrides this difficulty. It is shown that effective anchoring, using either mechanical anchors such as the ones devised by the authors or CFRP anchor ropes produced by the industry, can effectively upgrade the shear capacity of an RC T-beam under-designed in shear to the desired level. A novel laboratory test set-up, devised by the authors, can be utilized to quantify the tensile capacity of CFRP stirrups with or without anchors, that can be of practical use. The predicted, according to design guidelines, upgraded shear capacity of the tested prototype RC T-beam, employing the used shear retrofitting schemes, under-estimates the measured shear capacity by 58%. This conservatism can counter-balance uncertainties arising from in situ conditions in constructing the various parts of such a shear retrofitting scheme.