Stress-strain behaviour of FRP-confined concrete in eccentrically-loaded circular columns

Fibre-reinforced polymer (FRP) jacketing/wrapping has become a widely accepted technique for strengthening/retrofitting reinforced concrete (RC) columns. Although extensive research has been conducted on FRP-confined concrete columns under concentric compression, leading to many stress-strain models, the applicability of these concentric-loading (CL) stress-strain models in the analysis of columns under eccentric loading has not been properly clarified. This paper presents an in-depth investigation into this problem using an advanced three-dimensional (3D) finite element (FE) approach. The axial stress distributions and the stress-strain responses of FRP-confined concrete in circular columns under eccentric compression are examined using the FE results. It is shown that the stress-strain response of concrete varies greatly over the section and the direct use of a single CL stress-strain model for the entire section in the analysis of eccentrically-loaded columns may lead to significant errors, especially for the prediction of ultimate deformation/ductility. The paper also shows that a stress-strain model for the confined concrete at the extreme compression fibre of the section provides a relatively simple and much more accurate option for the analysis of eccentrically-loaded columns.