A unified failure envelope for hybrid fibre reinforced concrete subjected to true triaxial compression

A unified failure envelope for hybrid steel-polypropylene fibre reinforced concrete (HFRC) subjected to true triaxial compression is presented in this paper, aiming to predict the ultimate strength of HFRC under multiaxial compressions. The failure envelope based on a five-parameter failure criterion was developed which accounts for the presence of hybrid fibres. The model parameters were calibrated through true triaxial compression tests. The results showed that the steel fibres mainly contribute to the composite’s triaxial strength that was observed to improve significantly when both the volume fractions and aspect ratios of steel fibre were increased. On the other hand, the polypropylene fibres were found to have considerable effect on improving the tensile meridian rather than compressive meridian. Furthermore, the developed model was evaluated against existing experimental results of both plain concrete and fibre reinforced concrete. It was observed that, with the removal of fibres, the developed model can reverse to the model of plain concrete, and the prediction yields a close and mostly conservative approximation of the ultimate strength.