Dynamic Interaction Between Heavy Vehicles and Highway Bridges

Modern prestressed reinforced concrete bridges are designed per LRFD standards, and are lighter with smaller safety factors. At the same time bridges are loaded with heavier vehicles with substantial masses when compared to the mass of the bridge. It requires fairly detailed FE models of the vehicles (in addition to the FE models of the bridges) for a meaningful analysis of the vehicle-bridge dynamic system. Imperfections in road surfaces can trigger significant dynamic loads on the bridge with adverse effects, which are not well understood. FDOT issues over 90,000 permits for heavy vehicles every year, therefore finding newer, easier, and more economical ways to study and understand the actual impact of dynamic loads on bridges is critical for design and maintenance of highway bridges. The main goal of this research was to develop numerical models of heavy vehicles and bridges and to use them for transient analysis of dynamic interaction between the vehicle and the bridge. An assessment of three finite element (FE) vehicle models and one bridge FE model was carried out and the necessary improvements were implemented. Additional bridges in North Florida were surveyed, and two substructures were selected for modeling. The two selected bridges had different geometric characteristics and their FE models were developed according to AASHTO specifications. Three FE models of heavy vehicles were used with three different bridges for computational dynamics analysis using the LS-DYNA computer code. The influence of several factors such as vehicle mass and speed, road surface condition, and loosely secured cargo were assessed. Dynamic load allowance (DLA) was determined for each vehicle-bridge combination. Practical conclusions regarding methods to mitigate DLAs were presented.