The need of a unified method for strength and ductility analysis of strengthened concrete columns

The current paper reports selected findings from a research programme is being carried out at the United Southampton into the fundamental understanding of the effectiveness of FRP confinement, when applied to circular concrete columns as a means of improving strength and ductility. The paper shows that the predictions from the empirical formulae-based design guidelines recommended by The Concrete Society Technical Report No. 55 (the most widely used design standard in the UK) and ACI 440.2R-02 (the most widely used design standard in the USA) are unreliable. By comparing the predictions from the two design recommendations for a database of test results extracted from the published literature, the paper shows that the formulae do not provide correct results. The models do not effectively take into account of differences in the confinement provided by FRP jackets in large columns. Similarly, the less effective confinement exerted in high strength concrete, reduction in the rupture strain of thick (stiff) FRP jackets, effects due to the height / diameter ratio of the column cannot be incorporated into the models. In particular, the paper shows that although the predictions form the models agree well with the test results used to derive the original empirical formulae they do not provide accurate predictions for the failure load of new test specimens