Performance of fiber-reinforced polymer-wrapped reinforced concrete columnunder combined axial-flexural loading

This paper presents results of an experimental investigation into the perfo rmance of reinforced concrete beam-columns strengthened with externally app lied bidirectional carbon fiber-reinforced polymer material. The external m oment was applied to the specimens through corbels that were part of the co lumns. The overall length of the column specimens, including the corbels, w as 11.8 ft (3.6 m). Six series of rests were performed on the specimens. Th e first five series, corresponding respectively to eccentricities of 0, 3, 6 12, and 16 in. (0, 75, 150, 300, and 400 mm), were performed under a comb ined axial-flexural loading condition. The sixth series was tested in four- point pure flexure with no axial load. Results indicate that the strength c apacity of beam-columns improved significantly as a result of the combined action of the longitudinal and the transverse weaves of the bidirectional c omposite fabric. The longitudinal carbon fiber-reinforced polymer (CFRP) el ements contributed mostly to flexural capacity, whereas the transverse elem ents enhanced the compressive capacity of the compression zone through conf inement action. The maximum capacity gain achieved was slightly below 30% i n pure compression, and over 54% in pure flexure. Under combined axial forc e-bending moment conditions, the gain in moment capacity attained 70%. The increase in the compressive strain due to the confinement effect varied fro m 49 to 166%. The transverse confinement was engaged in the compression zon e from the early stage of loading. Finally, within the conditions and the l imits of this study, the proposed design procedure, based on the stress of confined concrete in the compression zone in conjunction with an effective confinement ratio that takes into account the rectangular shape of the beam -columns, compared reasonably well with experimental results.