Nonlinear fatigue damage assessment of existing bridges considering progressively deteriorated road conditions

Variable stress ranges from dynamic vehicle loads can induce fatigue damage accumulations at certain bridge components and accelerate the road surface deterioration in bridges’ life cycle. The interactions of the road surface deterioration and random dynamic vehicle loads might accelerate the fatigue damage accumulations and lead to serious fatigue failures when such damages increase to a certain limit. This paper presents a nonlinear fatigue damage assessment approach for existing bridges to include the progressive road surface deterioration and the nonlinear effects of the fatigue damage accumulation due to random dynamic vehicle loads. In each stress block for fatigue damage calculation, vehicle types and speeds and road profiles for a certain road roughness coefficient are randomly generated for the vehicle–bridge dynamic system. Fatigue damage and cumulative probability of fatigue failures due to these variable stress ranges are calculated based on a nonlinear cumulative fatigue damage rule. Nevertheless, the vehicle types, numbers, and weights are used to predict the road roughness coefficient for the next stress block. The predicted fatigue damages are different when using the linear and nonlinear fatigue damage rules. The effects from the random variables in the vehicle–bridge dynamic system are discussed, as well.