Design model for FRP-confined normal- and high-strength concrete square and rectangular columns

It is well understood that the confinement of concrete with fibre-reinforced polymer (FRP) composites can significantly enhance its strength and deformability. However, the effectiveness of FRP confinement on square and rectangular concrete sections, in which the concrete is non-uniformly confined, is much lower than the effective confinement of circular sections. To investigate the shape factors that influence the compressive behaviour of FRP-confined concrete in square and rectangular sections, current theoretical models are reviewed and a database of existing test results is assembled. The database is then studied, together with a companion database consisting of the test results of FRP-confined concrete in circular sections, in order to capture the change in the effectiveness of confinement due to the change in the sectional shape. The combined database records the compression test results of 1547 specimens with unconfined concrete strengths ranging from 6.2 to 169.7 MPa. It provides a significantly extended parameter space, thereby allowing clearer observations of the important factors influencing the compressive behaviour of FRP-confined concrete in various sections. The second half of the paper presents an assessment of the performance of existing models proposed to predict the ultimate conditions of the FRP-confined concrete in square and rectangular sections. Finally, a unified model for FRP-confined concrete in circular, square and rectangular sections is developed based on the observations from the databases.