Toward Safe and Efficient Use of Fiber-Reinforced Polymer for Repair and Strengthening of Reinforced Concrete Structures

Models for the evaluation of shear force resistance, adopted by current seismic codes, rely on the truss analogy (TA) theory. In contrast with the TA, the compressive force path (CFP) method employs a more rational representation of the compressive and tensile force fields within the entire length of the member under the axial load and transverse deformations imposed at the ultimate limit state. This article reports on a study undertaken to demonstrate the applicability of the CFP method, through design and testing to failure, showing that it can be used for the ultimate limit state design of the repair and shear strengthening of RC beam-columns under large inelastic deformations. The authors report on test results of eight linear members, tested at the Reinforced Concrete Laboratory of the National Technical University of Athens (Greece), under different normalized axial load and shear span-to-depth ratios. These specimens had been previously tested and subsequently repaired or strengthened using fiber-reinforced polymer (FRP) sheets. All specimens are retested under constant axial load and cyclic transverse load, similar to the virgin control specimens. Retest results indicate that, unlike specimens repaired/strengthened by conventional methods that failed early in a brittle manner, all the members repaired by the CFP method reached both the redesign strength and the ductility levels inherent in current earthquake-resistant performance-based design. The authors conclude that, depending on the axial load, repair with FRP sheets designed to the TA method cannot always ensure that the design aims are fulfilled with the same level of reliability as the CFP method. This is due to the presence of weak links in the force path prediction that are not considered by the truss model in the TA method, such as the point of zero bending.