Design-oriented stress-strain model for FRP-confined ultra-high performance concrete (UHPC)

Current axial stress-strain models of FRP-confined concrete mainly focus on FRP-confined normal concrete, the research work on studying the stress-strain behavior of FRP-confined ultra-high performance concrete (UHPC) is limited so far. To fill this research gap, this study develops a new design-oriented stress-strain model to predict the stress-strain relationship of FRP-confined UHPC cylinders under axial compression. The developed model has two versions, i.e., the Version I model is applicable to the specimens experiencing stress reduction, and the Version II model is a typical bi-linear model with a parabolic first portion and an ascending linear second portion. A large amount of compressive test data collected from five previous experimental studies involving 117 FRPconfined UHPC cylinders was used for the model development. The assessment results reveal that both versions of the developed design-oriented model have the capability of accurately estimating the characteristic stresses and strains at characteristic points. In addition, it is demonstrated that the full stress-strain curves predicted by the developed model agree reasonably well with most of the test results.