Monotonic Stress-Strain Behavior of Steel Rebars Embedded in FRP-Confined Concrete Including Buckling

Fiber-reinforced polymer (FRP) confining jackets offer an attractive solution for the seismic retrofit of RC columns. For the accurate prediction of strength and ductility of FRP-confined RC columns, it is necessary to understand interactions between the FRP jacket and the RC column at all deformation levels under seismic loading. In particular, when the transverse steel reinforcement consists of widely spaced steel stirrups or spirals, the longitudinal steel reinforcing bars (rebars) are likely to develop buckling deformations despite the lateral support provided by the FRP-confined concrete. This paper presents a theoretical study into the buckling behavior of longitudinal steel rebars embedded in FRP-confined concrete subjected to monotonic axial compression. In the theoretical model, a beam-on-elastic foundation idealization is used, where the steel rebars are laterally supported by elastic springs representing the FRP-confined cover concrete. To evaluate the stiffness of the elastic springs, a curved beam model is proposed. Predictions from the theoretical model are compared with test results, demonstrating the reliability of the theoretical model. A parametric study is then presented to examine the influence of three key factors (i.e., spring stiffness, yield strength of steel, and slenderness ratio of rebar) on the overall compressive stress-strain response of laterally supported steel rebars. Finally, an empirical compressive stress-strain model considering the effect of buckling deformation is proposed for steel rebars embedded in FRP-confined concrete subjected to monotonic axial compression and validated through comparisons with the test results.