Square and rectangular columns confined by FRP: experimental investigations vs ultimate strain prediction

Ultimate stress and strain prediction is an important issue to be solved in order to define the performance of FRP confined section. In case of circular section, the task can be considered as partially solved thanks to the several studies carried out. In case of square and rectangular sections, the difficulties due to the non-uniform confinement stress distribution are delaying the problem solution. Furthermore, the well-known problem of an objective definition and characterization of the ultimate strain increased the difficulty level: the strain of the confinement device, as well as the confinement efficiency, depends on the corner radius and is not uniformly distributed along the boundary section. Regarding the ultimate strength definition, an analytical solution has been proposed in a companion paper, while in this paper an experimentbased expression is proposed and validated against a set of experimental values collected in a database that includes also the tests carried out by the authors.