An improved criterion for sufficiently/insufficiently FRP-confined concrete derived from ultimate axial stress

This paper presents the assessment results of existing criteria for sufficiently/insufficiently fiber-reinforced polymer (FRP)-confined concrete, develops a unified ultimate axial stress model and proposes an improved criterion. The existing criteria for FRP-confined concrete in circular and rectangular columns are reviewed. A large database has been established by collecting the available experimental results from the open literature for evaluation of the existing criteria. The assessment results indicate that there is still room for improvement in the existing criteria, especially in those for rectangular specimens. An improved criterion for FRP-confined concrete in both circular and rectangular columns is proposed on the basis of the existing criteria and deduced from the unified ultimate axial stress model which is developed in this paper as well. Comparisons between the criterion predictions and the test results demonstrate the accuracy of the proposed criterion.