Analysis of axially loaded columns strengthened with fibre-reinforced polymer

When estimating the rectangular stress block of a reinforced concrete flexural member, it is important to take into account different behaviours due to load eccentricity, the ratio and type of fibre-reinforced polymer strengthening, specimen height and confinement ratio. To investigate the impact of these key variables on a rectangular stress block, an extensive analysis of an experimental database of 84 specimens reported by several independent research groups was undertaken. The accuracy and conservativeness of several models under axial compression and flexural loading were first assessed. Comparisons revealed overestimations for specimens strengthened with carbon-fibre-reinforced polymer and underestimations for those reinforced with glass-fibre-reinforced polymer. Inaccurate predictions were also obtained even after more accurate models of concentrically loaded tests were analysed using existing concrete design codes. Expressions for columns strengthened with fibre-reinforced polymer under pure axial compression and modifications for the coefficients of the rectangular stress block were developed. The results indicate a good and safe correlation of predicted strength values.