Impact of bonded carbon fibre composite on the shear strength of reinforced concrete beams

This paper reports on a study to determine the effectiveness of using externally bonded carbon-fibre-reinforced polymer composite sheets as a method of increasing the shear strength of reinforced concrete beams. The investigated parameters were the amount and distribution of the composite, the bonded surface and fibre orientation. The overall behaviour of the test beams up to failure, the onset of cracking and crack development with increased load and ductility were recorded. Beams strengthened with 90 degrees U-wrap composite sheet showed a large increase in ultimate-load-carrying capacity compared with beams strengthened with 90 degrees composite web strips of 50 mm width. Decreasing the spacing between the strips was also found to be efficient, while using 45 degrees strips rather than 90 degrees strips did not produce a remarkable increase in shear capacity. Depending on the variables investigated, the externally bonded composite increased the shear capacity by 34-75% compared with the control beams. Some previously published models were found to give consistently good correlations with the test data, with acceptable coefficients of variation. However, the model proposed by the American Concrete Institute showed unsatisfactory performance because of its empirical nature and use of an inappropriate model for bond length.