Behavior of FRP-confined ultra-high performance concrete under eccentric compression

This paper presents an investigation on the eccentric compressive behavior of fiber-reinforced polymer (FRP)-confined ultra-high performance concrete (UHPC). Twenty specimens with varied tube thicknesses and loading eccentricities were tested. The results indicated that nearly all specimens showed a strain-hardening behavior, except that several specimens with a very large loading eccentricity showed a strain-softening behavior. With the increase of the loading eccentricities, the load-carrying capacity and deformability exhibited a substantial reduction, while the tube thickness only showed a significant effect in concentric or small eccentricity cases. A finite element model was established, where UHPC was treated as a two-phase material and simulated with UHPC matrix and explicitly modeled steel fibers. An equivalent stress-strain relationship derived from the single fiber pullout test was proposed for the embedded steel fibers to provide a more accurate prediction for the fiber-matrix interfacial behavior. Based on a regression analysis of the experimental and numerical results, a design equation was developed to predict the ultimate load-carrying capacity of FRP-confined UHPC under eccentric compression.