Behavior and Modeling of Ultra-High Performance Concrete-Filled FRP Tubes Under Cyclic Axial Compression

Abstract This paper presents an experimental investigation and a stress–strain model for ultra-high performance concrete (UHPC)-filled fiber reinforced polymer (FRP) tubes under cyclic axial compression. Test results from 12 cyclically loaded and 18 monotonically loaded cylindrical specimens with different tube thicknesses, curing regimes, and steel fibers are presented. The influence of the tested variables on the envelope curve, plastic strain, and stress deterioration was clarified to establish a theoretical stress–strain model. Through a comprehensive assessment of well-known cyclic stress–strain model developed for FRP-confined conventional concrete, a new model for FRP-confined UHPC under cyclic axial compression is proposed based on a more rational consideration of the key characteristics of FRP-confined UHPC. Both the monotonic envelope response and the cyclic response showed good agreement between the analytic predictions based on the proposed model and the test results, confirming the capability of the proposed model to predict the cyclic axial behavior of FRP-confined UHPC.