Abstract: Stress-strain relationships of concrete circular columns confined by interlaminated hybrid fiber sheets of carbon fiber,aramid fiber,glass fiber,and basalt fiber are experimentally researched in this paper.Results show that HFRP can evidently increase the strength of circular columns,and significantly improve the ductility.Based on the experimental data and analysis on the research production,a constitutive confinement model is developed for concrete circular columns confined with HFRP.The feature of the model includes the effects of HFRP confinement on the concrete microstructure by evaluating the internal concrete damage using the axial,lateral,and volumetric strains,which introduces that the confinement model is simple and has a physical and fundamental interpretation with the mechanical behavior of concrete.Meantime,the secant concrete modulus is used in the model and expressed as a function of the secant modulus softening coefficient.The HFRP-confined concrete model accurately predicts the stress-strain relationship of concrete circular columns confined with HFRP as verified in comparison with experiments.