Stress-Strain Model of Ultrahigh Performance Concrete Confined by Fiber-Reinforced Polymers

The application of ultrahigh performance concrete (UHPC) as an alternative to conventional concrete has grown rapidly in recent years. However, to date, little is known about the confinement behavior of UHPC, knowledge that is necessary to develop design guidelines for UHPC columns. In a previous study, the authors investigated the stress-strain behavior of a series of UHPC-filled fiber-reinforced polymer (FRP) tubes with different fiber types and thicknesses under uniaxial compression. The FRP confinement was shown to significantly enhance both the ultimate strength and strain of UHPC. It was also shown that the existing confinement models are incapable of predicting the behavior of FRP-confined UHPC. Therefore, in this study, two commonly used FRP confinement models are recalibrated based on test results of FRP-confined UHPC. A model was further modified based on the stress-strain model of unconfined UHPC to better capture the linear response of UHPC before the activation of FRP confinement. A comparison of the three models showed that a recalibrated model provides the most accurate prediction of the stress-strain behavior of FRP-confined UHPC in terms of the stress-strain curve and ultimate strength and strain. (C) 2013 American Society of Civil Engineers.