Nonlinear cumulative damage model and application to bridge fatigue life evaluation

Fatigue is a damage accumulation process in which material property deteriorates continuously. Fatigue life prediction issues are important for safety. This article aims to develop a nonlinear cumulative damage model. A fatigue damage model based on the continuum damage mechanics is addressed and applied to bridge fatigue life evaluation. First, the bridge nonlinear cumulative damage model based on damage mechanics is propounded and equivalent effective stress range is given. Then, the effects of the main parameter in the model are analyzed. Finally, Xinghai Bay Bridge is taken as a case study. The results indicate that the damage is increased with the material parameter alpha reduced, alpha is a material parameter depending on stress amplitude and without physical meaning. If alpha > 20, the effect of alpha is negligible. If alpha = 0, nonlinear cumulative damage model degrades into Miner's rule and effect of alpha to structural damage is maximum. The cumulative damage curve calculated by the nonlinear cumulative damage model is nonlinear, with a low cumulative rate initially but a very high cumulative rate at the end of the design life, whereas the Miner's rule is linear. The nonlinear cumulative damage model can reflect actual damage process, while Miner's rule is pessimistic.