R.C. square sections confined by FRP: A numerical procedure for predicting stress–strain relationships

The effects of confinement on concrete elements subjected to axial load are well known: the resulting axial stress–strain relationship shows higher strength and ultimate strain with respect to the unconfined one. Several studies have been devoted to the understanding of the behavior of circular concrete sections while comparatively fewer studies have dealt with square and rectangular ones. Regarding square and rectangular sections, the so called “arching effect” is usually considered in order to define an equivalent reduced area, which is supposed as efficient as a circular section. Inside the equivalent area the stress induced by the confinement is considered uniformly distributed, even if it is not so, as already discussed in [17] where further on a strength criterion has been proposed for predicting the material strength increase, based on a revision of the classical strength criterion reported in [18]. That strength criterion, along with the methodology here proposed, are the basis of a procedure meant to develop a mechanics-based stress–strain relationship for FRP-confined concrete which stems from a step-by-step analysis of the behavior of FRP-confined square concrete sections.