Study of the stress-strain relationship of FRP-confined circular concrete column with a strain-softening response

The performances of circular concrete columns confined with FRP of various volumetric ratios and three different types of FRPs, including high strength FRP, high modulus of elasticity FRP and high ductility FRP, were tested. The FRP-confined circular concrete columns may or may not exhibit strain-softening. The maximum stress of FRP-confined concrete mainly depends on the confinement strength or the confinement modulus of FRP, while the axial ultimate strain of FRP-confined concrete is related not only to these two parameters but also to the ultimate tensile strain of FRP. Boundary values of the confinement ratio are suggested for determining the stress-strain curves of FRP-confined circular concrete columns with or without strain-softening. Based on the discussions on the effects of confinement strength and confinement modulus of FRP, the ultimate tensile strain of FRP, the strength and the modulus of elasticity of concrete, two stress-strain models as well as formulations for predicting the peak stress and the corresponding strain, the ultimate stress and the ultimate strain of FRP-confined circular concrete columns with strain-softening are proposed. The formulations and models demonstrate good agreement with experimental results from the present and previous studies.