Stress-Strain Model for FRP-Confined Concrete in Eccentrically Loaded Circular Columns

Extensive research has been conducted on FRP (fiber-reinforced polymers)-confined concrete columns under concentric compression, leading to many stress-strain models for such concrete. These concentric-loading (CL) stress-strain models have generally been used in the analysis of both concentrically and eccentrically loaded columns. Existing tests, however, have shown that eccentrically loaded FRP-confined concrete columns exhibit some behavioral aspects that cannot be closely predicted using a CL stress-strain model. This paper presents an in-depth investigation into this problem using an advanced three-dimensional (3D) finite element (FE) approach. The stress-strain response of concrete is shown to vary significantly 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 in the prediction of ultimate displacement/curvature. A stress-strain model for the confined concrete at the extreme compression fiber of the section is also shown to provide a relatively simple and much more accurate option for predicting the ultimate displacement/curvature of eccentrically loaded columns. Based on this conclusion, a so-called eccentricity-dependent (EccD) stress-strain model is proposed based on a comprehensive parametric study using the FE approach. The proposed model can be directly used in a section analysis or a theoretical column model and is proven to provide much more accurate predictions of the ultimate displacement/curvature of test columns than existing CL stress-strain models.