Triaxial Strength and Failure Criterion of Ultrahigh-Strength Concrete

The mechanical properties and failure criteria of ultrahigh-strength concrete (UHSC) with uniaxial strength over 100 MPa were studied under triaxial compression. Various confining pressures from 0 to 30 MPa were applied in the tests to investigate the confinement effect on UHSC. Through the triaxial test, the failure mode of the specimen was observed. The complete stress–strain curve and characteristic point parameters of triaxial stress–strain were analyzed, and the variations in strength and deformation performance indexes of UHSC were also revealed under different confining pressures. The experimental results showed that with the increase in confining pressure, the peak stress and peak strain increase, and the stress–strain curve of the peak stress becomes smoother. The failure criterion for UHSC, based on the Ottosen four-parameter model, has been established. In addition, formulas for calculating peak stress, peak strain, parametric constitutive equation, and volumetric strain of UHSC under triaxial compression align well with experimental data. Finally, the effects of confining pressure on the peak compressive strength are compared across different levels of concrete strength through normalization.