Failure criteria and stress-strain constitutive envelope surfaces for UHPFRC with different volume fractions of steel fibers under triaxial compression

Abstract

Ultra-high-performance fiber-reinforced concrete (UHPFRC) often withstands triaxial stress in practical engineering structures. However, research on the mechanical properties of UHPFRC under triaxial compression is limited. The influence of different volume fractions of steel fibers on the triaxial mechanical properties of UHPFRC has not been detailly revealed. Triaxial compression tests were conducted on 54 UHPFRC specimens, and different volume fractions of steel fibers (1.5 %, 2.0 %, 2.5 %) and confining stresses (0 ∼ 50 MPa) were considered. The experimental results indicate that for UHPFRC specimens with volume fractions of steel fibers, the failure modes of all specimens first changed from oblique shear failure to shear and compression failure as the confining stress increases from 0 MPa to 50 MPa. The greater the confining stress, the greater the peak stress and peak strain. The triaxial compression strength of UHPFRC first increases and then decreases as the volume fraction of steel fibers increases. The octahedral stress-strain relationships were discussed, and a quadratic function relationship between the octahedral peak shear stress and shear strain is obtained. On the basis of the octahedral stress-strain relationships, three triaxial compression failure criteria including Mohr-Coulomb, Willam-Warnke, and Bresler-Pister criteria were carefully discussed. The prediction accuracy for the experimental values of the Mohr-Coulomb criterion is better than that of the Willam-Warnke and Bresler-Pister failure criteria. However, for different types of UHPFRC, the distribution patterns of the predicted values calculated using the Willam-Warnke and Bresler-Pister failure criteria have better consistency compared to those of the Mohr-Coulomb criterion. Finally, envelope surfaces of stress-strain constitutive curve for UHPFRC were proposed. The research results provide a theoretical basis for promoting the engineering application of UHPFRC with different with different volume fractions of steel fibers.