Design-oriented stress–strain model for RC columns with dual FRP- steel confinement mechanism

Many research studies have been conducted to evaluate confinement-induced enhancements on the mechanical properties of FRP (fiber-reinforced polymers)-confined plain concrete elements subjected to axial compressive loading, leading to the development of extensive predictive models. Nevertheless, experimental stress–strain results for FRP-confined RC columns (FCRC) have demonstrated some behavioural features that cannot be simulated accurately through this kind of model, developed exclusively for FRP-confined concrete columns (FCC). In this paper, a new design-oriented stress–strain model is proposed for the prediction of load-carrying capacity versus axial strain relationship of FCRC. For this purpose, a new parabolic stress–strain expression is developed for calculating the first branch of FCRC's response up to the transition zone, followed by a linear function. New formulations are proposed to determine the first branch's stress–strain gradient, transition zone-related information and the second branch's slope, calibrated using a large test database of FCRC. The proposed design-oriented model is capable of simulating accurately the combined influence of the dual FRP and steel confinement on load-carrying capacity versus axial strain relationship of FCRC. Lastly, the capability of this model is validated by comparison to existing experimental data of FCRC and those obtained from some of existing models in the literature.