Stress-strain model for circular concrete columns confined by FRP and conventional lateral steel

Behavior of reinforced concrete columns confined by Fiber Reinforced Polymer (FRP) or conventional lateral steel (tie/spiral) reinforcement has been studied extensively by many researchers. Although FRP wrapping is used when lateral steel is not sufficient to confine the concrete core, the ability of lateral steel to provide confinement in most of the cases is not negligible. A constitutive stress-strain model is proposed for concrete confined by FRP and conventional lateral steel reinforcement when they act simultaneously. The accuracy of the proposed model in predicting the monotonic stress-strain relationship of concrete confined by both FRP and conventional reinforcement is assessed compared to various experimental data from specimens tested under concentric monotonic load, and several representative models. Additionally, the moment-curvature response of a section, using the proposed model in a fiber-based analysis, is compared and benchmarked against several independent experimental results.