Failure Criterion of Ordinary Concrete Subjected to Triaxial Compression of Full Section and Local Loadings

In this paper, experiments carried out on ordinary concrete under multiaxial compression of both full section and local section are presented and the failure modes compared under different loading conditions. According to the stress–strain curves obtained in true triaxial compression experiments, the mechanical properties of ordinary concrete were also extracted under different loading conditions, including full section loading and local loading. Because of the confining pressure, as for full section loading, the peak stresses under multiaxial compression were 1.27–2.27 times higher than those under uniaxial compression, whereas for local loading, the multiple was 1.24–2.05 times. It is obvious that the increasing coefficients under full section compression are more susceptible to confining pressures than those under local compression. The unique point of the experimental method is that ordinary concrete was subjected to full section or local uniaxial compression after full section or local triaxial compression. In this way, the failure modes of ordinary concrete were clearly revealed owing to the initial damage caused by triaxial compression. Meanwhile, the residual mechanical properties of ordinary concrete that had been subjected to full section or local triaxial compression were obtained, contributing to a comprehensive understanding of the mechanical properties of ordinary concrete under triaxial compression. Then a failure criterion of ordinary concrete under local loading was proposed based on the data of true triaxial compression experiments. The failure criterion was verified using data of both relevant scholars’ experiments and independent experiments of local triaxial loading. The results showed that the proposed failure criterion was simple but effective enough to compute the failure strength of ordinary concrete.