A damage-based life prediction model of concrete under variable amplitude fatigue loading

This work investigates damage characteristics and fatigue life of plain concrete subjected to flexural loading. This type of fatigue loading is of concern in the design of concrete bridges, seashore structures, and concrete pavement slabs since the flexural stresses in these structures can be critical. Both laboratory experiments and theoretical analysis have been conducted. Concrete beam specimens were prepared and tested in fourpoint bending under constant amplitude fatigue loading condition. The maximum displacement was recorded during the tests and used as a damage parameter to establish a 'damage curve' at different stress levels. The damage curves relate the damage propagation to the increase in the number of loading cycles. By implementing the damage curves and the cubic spline surface fitting technique a 'damage surface' has been introduced. The damage surface relates the damage to the number of loading cycles and the stress level. A damage mechanics based model, that utilize the damage surface, is proposed to predict the fatigue life of plain concrete. The proposed model is able to account for the nonlinear propagation and accumulation of damage and can model the effect of the magnitude and sequence of variable amplitude fatigue loading. Two-stage variable amplitude fatigue tests were performed to examine the validity of the proposed model. The model shows close agreement with the test results. The present study indicates that the fatigue life of concrete is greatly influenced by the magnitude and sequence of applied variable amplitude loading. It is seen that the linear damage theory proposed by Miner is not applicable to concrete under such loading cases. The proposed non-linear damage model, which includes the effects of the magnitude and sequence of applied fatigue loadings, allow for more realistic fatigue analysis of concrete structures.