Analysis-oriented stress–strain models for ultra-high-performance concrete confined with fiber-reinforced polymer

The use of fiber-reinforced polymer (FRP) jackets or tubes as confining devices can significantly improve the compressive performance of ultra-high-performance concrete (UHPC). For FRP-confined UHPC, an analysis-oriented stress–strain model is essential for a comprehensive understanding of its compressive behavior and the development of design models. Although several analysis-oriented stress–strain models have been developed for FRP-confined normal-strength concrete (NSC), such models for FRP-confined UHPC are still lacking. In this study, an experiment is conducted to investigate the failure mechanism of UHPC confined with FRP under concentric compression, and the stress–strain behavior of the FRP-confined UHPC is analyzed using the stress–strain models of actively-confined UHPC. Results showed that the stress-path-independency assumption, which has been proven to apply to FRP-confined NSC, was inapplicable to FRP-confined UHPC. By modifying the confining pressure to consider the influence of stress-path dependency, an analysis-oriented model was proposed. The proposed model was verified using a collected test database. The results show that the proposed model accurately predicted the stress–strain behavior of FRP-confined UHPC.