Confinement-dependent failure criterion for high-strength concrete in multiaxial stress states

High-strength concrete is becoming progressively wide applications in modern civil engineering structures because of its excellent mechanical properties and workability. However, most of the commonly adopted failure criteria were developed based on the low-strength concrete (cylinder compressive strength less than 40 MPa), and they may not accurately reflect the behavior of high-strength concrete due to the changes in its failure modes from intergranular failure to transgranular failure. The systematic analysis of databases consisting of 2120 experimental results of concrete multiaxial test collected from a wide range of existing literature has been carried out. It was found that the ratios of concrete ultimate strengths under uniaxial tension and equibiaxial compression to its uniaxial compressive strength (fc0) were negatively correlated with the uniaxial compressive strength. While under triaxial compression, the ultimate strength enhancement was affected by the uniaxial compressive strength and the degree of confinement (sigma m/fc0) simultaneously. On this basis, through the careful discussion of the morphological characteristics of concrete cracks after multiaxial failure, the concepts of the weakly and heavily confined states of concrete under triaxial compression were developed quantitatively, and the critical degree of confinement sigma m/fc0 =-0.8 was proposed. Under the heavily confined state, the ultimate strength enhancement of the high-strength concrete was less than that of the low-strength concrete, whereas there was no difference between them under the weakly confined state. A confinement-dependent failure cri-terion was formulated that utilized the piecewise compressive meridian to achieve a more rational description of the multiaxial ultimate strength for high-strength concrete. With the suggested failure criterion, a peak axial stress model for confined concrete was proposed. As verified by the experimental data of concrete confined by fiber-reinforced polymer (FRP) wraps from existing literature, which contains both high-strength and low -strength concrete, the proposed model showed better prediction accuracies with less scatters than the existing counterparts. This study can also be a reference for the research of the multiaxial failure criterion of other concrete-type materials.