Vehicle Weight Limits and Overload Permit Checking Considering the Cumulative Fatigue Damage of Bridges

The ever-increasing demand in freight transportation results in a fast-growing number of overload permit requests every year. Overweight trucks, if not properly managed, can induce excessive fatigue damage that could significantly reduce bridges' load-carrying capacity and affect their durability. Therefore, developing rational vehicle weight limits and procedures for overload permit checking is very important to ensure the safety of bridges. In the current practice of overweight vehicle management, a permit decision is usually made by checking the ratio of the load effect imposed by the overweight truck to the design vehicle load effect against an allowable limit. The fatigue damage on the bridge due to the repeated vehicular loads and its influence on bridges' load-carrying capacity are usually ignored. The widely adopted federal bridge formula in the United States has also been criticized as being too restrictive for vehicles with certain axle configurations. In this article, a method for determining vehicle weight limit and overload permit checking is proposed based on the consideration of the cumulative fatigue damage of bridges. A typical steel-concrete composite girder bridge is used as an example for illustrating the proposed method. Based on the results from this study, the rationality of the federal bridge formula is discussed. The results from this study can not only be used to develop vehicle weight limits and assist in overload permit checking but also to assess the fatigue damage and predict the remaining fatigue life of existing bridges.