Strain Gradient in FRP-Confined ECC Columns under Eccentric Compression and Simplified Strength Model

Abstract Fiber-reinforced polymer (FRP)-confined engineered cementitious composite (ECC) columns are of interest as hybrid members due to their structural and durability characteristics. Although eccentric loading is critical in column design, studies on FRP-confined ECC columns under such loading remain limited. This paper examines the axial and eccentric compression mechanisms of glass FRP (GFRP) and large rupture strain (LRS) FRP-confined ECC columns and proposes an axial load–axial displacement model that accounts for strain-gradient effects. The model links the strain gradients induced by eccentric compression to the development of the confinement force gradient, from which analytical expressions for the confinement force under different eccentricities are derived. The results demonstrate that the proposed model can accurately capture the mechanical response of GFRP/LRS FRP-confined ECC columns under eccentric loading. A parametric investigation was conducted to quantify the effects of FRP confinement stiffness, load eccentricity, and core material type on the axial load–axial displacement relationship. Moreover, based on a compiled database of eccentric-compression results, a simplified model was developed to predict the strength of FRP-confined ECC or normal concrete columns under eccentric loading. Compared with existing models, the simplified model exhibits improved accuracy and robustness, thereby providing a practical, straightforward, and computationally efficient tool for engineering design and assessment.