Direct tensile behaviors of steel-bar reinforced ultra-high performance fiber reinforced concrete: Effects of steel fibers and steel rebars

Based on strengthening the structural performance of ultra-high performance fiber reinforced concrete (UHPFRC), a steel-bar reinforced ultra-high performance fiber-reinforced concrete (R-UHPFRC) is presented in this study. To provide more information about the direct tensile behaviors of R-UHPFRC member, several dogbone-shaped R-UHPFRC specimens are tested, with the experimental variables including the volume content of steel fiber and the reinforcement ratio of steel rebar. The effects of the fiber volume fraction and reinforcement ratio of steel bars on the direct tensile properties of R-UHPFRC are evaluated using multiple performance parameters, including load-deformation relationship, tension-stiffening behavior, tensile stiffness and damage pattern. Test results indicate that there is minimal difference in overall load-elongation responses of R-UHPFRC specimens with an increasing fiber volume fraction. The variation in the reinforcement ratio of the steel bar, by contrast, has significant influence on the tensile responses of R-UHPFRC specimen, especially the peak strength and hardening modulus increases considerably with a growing reinforcement ratio as compared to non-reinforced UHPFRC specimens. Importantly, the tensile strain values of R-UHPFRC with rebars are significantly higher than the counterparts of UHPFRC without rebars, and this rising trend is even more pronounced when the reinforcement ratio increases. Further, the use of R-UHPFRC with combined reinforcements is beneficial to extend the strain hardening capacity of UHPFRC itself. Even, a desired post-peak ductility can be achieved by a rationally designed reinforcement ratio of steel bars. The increased reinforcement ratio of steel rebars transfers the tensile failure pattern of the R-UHPFRC members from a single, localized crack into multiple localized cracks. (C) 2020 Elsevier Ltd. All rights reserved.