Flexural properties of ultra-high performance fiber reinforced concrete based on three-dimensional random distribution of steel fibers

The distribution of fibers and the fiber bridging affect the flexural strength and energy dissipation of ultra-high-performance fiber reinforced concrete (UHFRC) members. In this study, an analytical model to predict the flexural behavior of UHPFRC was developed based on the three-dimensional random distribution of fibers. The probability distribution model of the fiber orientation was developed as a sine function, which agreed to the measured probability data from the randomly distributed fiber specimens. The number of fibers at the fracture surface was determined addressing the effect of fiber orientation. Based on the proposed model, the method to predict the load–deflection curve of UHPFRC beam was suggested addressing the fiber bridging stress at fracture surface and tension softening effect. For verification, the four points flexural tests were conducted for six UHPFRC beam specimens. The test results showed that the peak flexural strength and energy dissipation can be predicted by the proposed model. Further, the proposed model was applicable to predict the strength and deformation capacity of existing test specimens. Based on the proposed model, the aspect ratio of fibers to prevent the brittle failure due to fiber rupture was suggested addressing the fiber tensile strength and bond strength.