Extensive researches in the past decades have demonstrated that FRP Jackets increase load carrying capacity and ductility of concrete columns which are one of the most important structural elements from the stand point of retrofitting. In addition, FRP confinement increases concrete strength. Therefore, applicable relations for computation of confined concrete strength are a necessity in design and analysis of concrete structures. Several studies have been performed on FRP wrapped circular and rectangular concrete columns and various models are proposed for calculation of confined concrete strength. Most of these existing models, which are derived from experiments on cylindrical concrete samples, are modifications of the well-known formula of Richart et al. It is proved that the FRP retrofitting is less effective in rectangular columns due to non-uniform distribution of confinement pressure. Consequently, many relations of the existing strength models for circular columns are reviewed and their accuracy compared. The comparison is conducted based on experimental results of various researchers. Moreover, two new strength models for short confined circular column are proposed using nonlinear regression techniques. Numerical evaluations verify the suggested relation accuracy in comparison with the existing models.

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