Compressive behavior of large rupture strain (LRS) FRP-confined square concrete columns: experimental study and model evaluation

A large rupture strain (LRS) fiber reinforced polymer (FRP), with a rupture strain value of more than 5%, is a promising alternative to traditional FRPs with a 1-3% rupture strain for seismic retrofitting of reinforced concrete (RC) structures. The LRS FRPs provide a bilinear stiffness around concrete columns while this feature is linear for traditional FRPs (e.g., carbon FRP). This paper presents a careful analysis of the compressive behavior of LRS FRP wrapped square column, especially since their confining stress is nonuniformly distributed. A total of 66 square concrete columns, measuring 150 x 150 x 300 mm with varied corner radii from 0 to 75 mm were tested under monotonic axial compression. The experimental results, in terms of full stress-strain behavior, compressive strength, hoop strain distribution, and dilation behavior were systematically investigated. As the corner radius increases, the strength enhancement after LRS FRP confinement also increases, and the hoop strain is more uniformly distributed. The stress-train curves exhibit a triple-section pattern with a smooth transition zone. The peak dilation rate of LRS FRP-confined concrete is higher than that of traditional FRP-confined concrete, and the curve of dilation rate versus axial strain exhibits a remarkably long stable response. Moreover, results show that most existing models of FRP-confined concrete can provide conservative predictions for an improved compressive strength of LRS FRP-confined square concrete columns.