Mechanical behaviour of concrete under triaxial compression — Loaded along paths in(stress, train, train) pace

Under the condition that was similar to plane-stress state, true triaxial tests were conducted on concrete cubes with the length of 100 mm. Loading process comprised of two steps: (1) keeping the three axial stresses equivalent, compressive stress was increased to lOMPa, which was maintained for a period of time;(2) on the basis of keeping the stress in z axis as well as the stress rate ratio between x and y axis remained constant, strain in y axis was increased monotonously. Test was divided into four groups, 2~3 specimens for each group, and there are four types of stress rate ratios: 0.25, 0.5, 0.75 and 1.0. Full relationship curves of three axial stresses and also curves between strain in z and y axis were developed, from which, it is found that, with loading processing, the maximum and intermediate principal stresses interchanged with each other; in the axis of maximum principal strain (Y axis), the stress rate ratio and intermediate principal stress had little influence on the peak stress and its corresponding strain, for peak stress the fluctuation was less than 9%, and less than 20% for peak strain; in the second phase of loading, the relationship between z and y axis tended to be curves near the starting point, but became linear when the variation quantity of strain in y axis exceeded 0.015, and the slopes of linear parts varied monotonously with the stress rate ratio altering.