Non-uniform stress distribution in FRP-wrapped circular concrete columns under uniform axial deformation

The confinement of concrete columns using bonded FRP wraps has become a popular retrofit technique. Through extensive research in the last two decades, many stress-strain models have been developed for concrete in FRP-wrapped circular columns. All these models assume that the stress state is axisymmetric in an FRP-wrapped circular concrete column under concentric axial compression. This implies that the FRP wrap is assumed to be axisymmetric in geometry, but in reality such axisymmetry is not realised due to the existence of an overlapping zone. This paper presents a finite element investigation into the stress state in FRP-wrapped circular concrete columns considering the actual FRP wrap geometry used in laboratory tests and practice. The results show that common FRP wraps with an overlapping zone can lead to significant non-axisymmetric confinement to the concrete and hence a significantly non-uniform stress distribution in the concrete, even when the concrete is under uniform axial shortening.