Abstract: In recent years several parallel bridges were designed and built in North America. These bridges have been selected to replace existing structures and to meet the ever-increasing demands of vehicle traffic. To meet the demands of increased traffic, the parallel configuration is often selected where each bridge deck carries traffic of opposite direction. This pair of decks, even when remaining dynamically independent, become coupled aerodynamically due to their proximity. In this configuration the aerodynamic forces can be enhanced by the similar cross-sections of each bridge and by the close dynamic properties of the twin structures. Becoming aerodynamically coupled, these twin-deck systems have been found to display aerodynamic behavior noticeably different to what could be expected from a single deck of the same cross-section. Typical known aerodynamic solutions to cure instabilities such as vortex shedding and flutter may not be as efficient for these cases. The conventional strategy to study each deck dynamically suspended upwind or downwind of the other statically-mounted deck section showed limited application given the new and complex motion-driven aerodynamic behavior that appeared only in a tandem dynamic arrangement of testing. Generally, there are slight geometrical differences in the twin sections (e.g., a walkway on one of the decks) and these difference lead to asymmetries in the combined cross-section. Therefore, finding an aerodynamic solution for one wind direction will not necessarily work for the opposite direction. Given that known solutions of a single section may not be efficient, and vice versa when considering bridge’s construction, an extensive circle of trials was required until appropriate aerodynamic solutions were found applicable in all conditions. This paper presents results of the aerodynamic studies for three different bridges, and of particular solutions found when required. Useful suggestions for future twin-bridge configurations of similar arrangements are also given.
Keywords: Parallel deck bridges, tandem section aerodynamics
