Cyclically loaded elliptical FRP-confined concrete: Behavioral characteristics and modeling

The previous studies on elliptical concrete confined with fiber-reinforced polymer (FRP) are mainly concerned with their monotonic compressive responses. By contrast, no research has been focused on their performance under cyclic axial loading. Motivated by this research gap, the behavioral characteristics of cyclically compressed elliptical FRP-confined concrete (FCC) were investigated in this research. The experimental parameters included the aspect ratio varying between 1.0 (circular section), 1.3, 1.7 and 2.0, the number of FRP layers, and the loading pattern (monotonic loading or two schemes of cyclic loading). The results revealed that plastic strains and stress degradation in elliptical FCC were confinement-independent parameters, regardless of confinement efficiency (affected by sectional geometry) and confinement level (governed by FRP thickness). This was similar to the case of cyclically loaded rectangular FCC (characterized by depth-to-width ratio). Moreover, the mechanism of non-uniform hoop strain distribution was dominated by two aspects, namely curvature radius-induced varying confinement stiffness and concrete cracking-induced strain localization. In contrast, the cyclic loading had a marginal effect on this distribution. Based on the monotonic model (considered as envelope curve) for elliptical FCC and the hysteretic rules originally for circular FCC, the complete compressive behavior of cyclically loaded elliptical FCC could be modeled with favorable accuracy.