FRP rupture strains in FRP-wrapped circular concrete columns: a combined experimental and finite element study

Strengthening concrete columns using bonded FRP confining wraps has become a popular retrofit technique. Failure of an FRP-wrapped column is usually governed by rupture of the FRP in the hoop direction. Numerous experiments have shown that the hoop strain at failure is significantly lower than the FRP rupture strain determined from tensile coupon tests. Many factors may contribute to this complex phenomenon. This paper is concerned with one of these factors, namely, the geometrical discontinuities at the ends of the FRP wrap. This paper first presents results from axial compression tests on six FRP-wrapped concrete columns, in which the particle image velocimetry (PIV) technique was used to obtain continuous strain distributions near the ends of the FRP wrap. A three-dimensional finite element (FE) investigation is then presented, which considered the actual FRP wrap geometry in the laboratory tests and adopted an advanced plastic-damage model for concrete. A comparison between the experimental and the FE results demonstrates the validity of the FE model and clarifies the significance of the effect of geometrical discontinuities on strain concentrations in the FRP wrap.