DAMAGE STUDY ON CONCRETE FATIGUE IN TENSION UNDER MULTI-LATERAL PRESSURES BASED ON RESIDUAL STRAINS
The tensile fatigue experiments of concrete for constant and variable amplitudes under multi-lateral pressures of 0.25fc, 0.50fc and their combination, respectively were conducted. The cumulative ultimate strain, the ultimate residual fatigue strain, and the relationships between the residual strains and the number of cycles were obtained. It is found that the residual strain was independent of loading history, and was mainly affected by lateral stress levels and the ratio of cycles. A united equation between damage variable and the cycle ratio was developed based on the damage variable defined as the ratio of residual strain to that of ultimate one. Therefore, the ratio values of cumulative strains and the static peak ones under the same stress level were compared with that of ultimate residual strains. It is shown that the ultimate strain increased with lateral stress accordingly; the influences of lateral stress level on ultimate stains were proved; on the other hand, the static peak strains approached the ultimate cumulative fatigue strain. The ratio values between the ultimate residual fatigue strain, the static peak strain and the ultimate cumulative strain of fatigue were stable. The variation range is from 0.22 to 0.28, and the deviation of the two ratios is 0.0 to 0.2. In the end, the variable amplitude fatigue lives were predicted by the modified Miner rule and the proposed damage models, the results were suitable.