Performance of Fiber-Reinforced Polymer-Wrapped Reinforced Concrete Column under Combined Axial-Flexural Loading

This paper presents results of an experimental investigation into the performance of reinforced concrete beam-columns strengthened with externally applied bidirectional carbon fiber-reinforced polymer material. The external moment was applied to the specimens through corbels that were part of the columns. The overall length of the column specimens, including the corbels, was 11.8 ft (3.6 m). Six series of tests were performed on the specimens. The 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 combined axial-flexural loading condition. The sixth series was tested in fourpoint pure flexure with no axial load. Results indicate that the strength capacity of beam-columns improved significantly as a result of the combined action of the longitudinal and the transverse weaves of the bidirectional composite fabric. The longitudinal carbon fiber-reinforced polymer (CFRP) elements contributed mostly to flexural capacity, whereas the transverse elements enhanced the compressive capacity of the compression zone through confinement action. The maximum capacity gain achieved was slightly below 30% in pure compression, and over 54% in pure flexure. Under combined axial force-bending moment conditions, the gain in moment capacity attained 70%. The increase in the compressive strain due to the confinement effect varied from 49 to 166%. The transverse confinement was engaged in the compression zone from the early stage of loading. Finally, within the conditions and the limits 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.