The need of a unified model for strength analysis of strengthened concrete columns

The current paper reports selected findings from a research programme carried out at the University of Southampton into the fundamental understanding of the effectiveness of FRP confinement, when applied to circular concrete columns as a means of improving strength. The paper shows that predictions from the empirical formulae-based design guidelines recommended in The Concrete Society Technical Report No. 55 (the most widely used design standard in the UK) and ACI 440.2R-02 and ACI 440.2R-08 (the most widely used design standards in the USA) are unreliable. By comparing predictions from the code formulae for a database of test results, extracted from the published literature, the paper shows that the formulae fail to provide correct failure load. The paper shows that the models do not take into account of the effects due to: for instance, low confinements in high strength concrete, rupture strain of FRPs, change in the FRP rupture strain in jackets with multiple layers, and localised FRP failures likely to happen in large diameter columns, etc. In particular, it is shown that, although predictions form the Concrete Society model generally agree with the test results used to derive the original empirical formulae, it does not provide accurate predictions for failure load of new test specimens. The paper also identifies key design parameters, which may be incorporated in an accurate unified model to predict strength of FRP-confined columns. © 2013, NetComposite Limited.