RC square sections confined by FRP: Analytical prediction of peak strength

During the last ten years, several studies have been devoted to understanding the behavior of circular concrete sections confined by FRP. Comparatively fewer studies have dealt with square and rectangular cross-sections, even if the problem is equally important, since those are the most common shapes one can find in buildings in need of retrofitting with respect to vertical and horizontal actions.A practical approach to this problem could be to develop predictive equations through regression of experimental results. The resulting equations, even if well calibrated, fail to interpret the real nature of the underlying physical phenomena. Other approaches are based on the so-called “arching effect”, by which, without any reasonable explanation, a convenient geometric subdivision of the square/rectangular section into confined and unconfined regions is performed.With the aim of clarifying the real nature of the problem, an analytical model is here proposed for predicting the ultimate strength of FRP-confined square cross-sections, based on a revision of a classical strength criterion [34]. Since the model considers the corner rounding radius influence, circular sections are automatically included as a particular case.The predicting equation was tested against a large set of experimental values available in the literature: the accuracy of the model is discussed, showing that the comparisons, in terms of average absolute error and average ratio, were satisfactory.