Fatigue Design of Steel Bridges Considering the Effect of Dynamic Vehicle Loading and Overloaded Trucks

The current practice for bridge-fatigue design may have underestimated the effect of dynamic vehicle loading and truck overloading on the fatigue life of steel bridges. In this study, a new approach for fatigue design of steel bridges was proposed that considers the effect of these two factors more rationally. A three-dimensional vehicle-bridge coupled model was developed to simulate the interaction between the bridge and vehicle. A simply supported steel I-girder bridge was used as an example for illustration of the proposed approach. The fatigue vehicle model was adopted from the AASHTO LRFD code, and overloading was considered by increasing the gross weight of the truck model. Numerical simulations were conducted to study the influence of three important parametersroad surface condition (RSC), vehicle speed, and truck gross weighton the fatigue damage of the bridge considered. The results show that the RSC and truck gross weight both have a significant impact on the bridge-fatigue damage. By considering the cumulative fatigue damage caused by each truck passage under different RSCs and the deterioration process of the RSC during its whole lifecycle, a simple and reasonable expression was proposed for bridge-fatigue design. The proposed approach improves the current bridge-fatigue design method in that it rationally considers the vehicle dynamic effect, the influence of overloaded trucks, and the deterioration of RSC, which have a large influence on bridges' fatigue life.