Characteristics and Dynamic Impact of Overloaded Extra Heavy Trucks on Typical Highway Bridges

Overloaded trucks, including some extra heavy trucks, often cause serious threats to bridges, such as deterioration, fatigue damage, or even collapse. Compared with the standard traffic design loads in design specifications, the actual characteristics of overloaded trucks, such as truck weight and types, are very difficult to predict or define. These characteristics are not specific only to the location. Rather, they depend on the economy, regulations, and law enforcement, and also vary over time as a result of uncertainties at a given location. In the current study, long-term traffic monitoring data are statistically studied to identify the key characteristics of extra heavy trucks, such as vehicle type, lane distribution, speed, axle weight, axle distance, and the variation of flow rate over time. All of the trucks from the traffic monitoring data are classified into 17 typical vehicle types, in which a total of 1,319 extra heavy truck scenarios are extracted from the traffic monitoring data. To study bridge performance under extra heavy trucks, advanced bridge/traffic interaction analysis software is developed and used to analyze the selected traffic scenarios. The bridge response and the dynamic amplification factors (DAFs) for a typical medium-span highway bridge are numerically investigated. Finally, these DAFs and bridge responses are compared with those as specified in both the AASHTO LRFD bridge design specifications and Chinese codes.