Fatigue life and change in mechanical properties of plain concrete under triaxial deviatoric cyclic stresses

The effects of a lateral confinement on the fatigue behaviour of plain concrete are experimentally investigated. Triaxial cyclic tests on cylinders, with confining pressure and axial load varying in phase opposition at 1 Hz, were performed in different deviatoric planes. The maximum stress deviator was 90% of the deviator at failure in a given deviatoric plane; the minimum deviator ranged between 70% and 95% of the maximum one. The residual strength and stiffness properties of those specimens that did not fail within a prescribed number of cycles were also assessed. For tests with cycles of equal amplitude (normalized to the triaxial static strength), fatigue life and residual strength seem to be positively affected by an increase in hydrostatic stress only up to a certain level. With the maximum deviator equal, in a given deviatoric plane fatigue life usually increases with decreasing cycle amplitude. In one of the deviatoric planes, cycle amplitude and mean stress were found to have opposite effects upon damage and residual strength.