Aerodynamic Characteristics and Wind Load Partitioning in Double-deck Girders: Effects of Inter-deck Clearance Height

The inter-deck clearance height (IDH), defined as the vertical distance between decks, is a key parameter in the aerodynamic design of double-deck bridges. This parameter governs both global aerodynamic characteristics and the allocation of wind loads across different subcomponents (top/bottom decks, windward/leeward trusses) of the girder, yet its effects remain underexplored. This study examines the effects of IDH using five double-deck girders with varying IDH, combining wind tunnel tests and Computational Fluid Dynamics (CFD) simulations. Results show that the drag and lift (absolute) coefficients increase with IDH, notably at high angles of attack. For all investigated girders, roughly half of the average drag is sustained by the windward truss. Furthermore, as the IDH increases, the mean drag force borne by the leeward truss increases, whereas the share carried by the top/bottom decks decreases correspondingly; meanwhile, the primary contributor for the fluctuating drag force shifts from the leeward to the windward truss. In contrast, both the mean and fluctuating lift force are primarily carried by the decks, with the trusses having a negligible contribution, and this partitioning pattern remains unchanged regardless of IDH. Furthermore, Dynamic Mode Decomposition (DMD) reveals that increasing IDH enhances flow instability near the windward truss while suppressing vortex development in the leeward region, leading to a shorter downstream persistence of wake structures. These findings provide insights into the underlying flow mechanisms and offer guidance for the aerodynamic selection and wind-resistant design of double-deck bridges.

کلیدواژه ها:

Double-deck bridge girder ، Inter-deck clearance height ، Subcomponent load partitioning ، Computational fluid dynamics ، Dynamic Mode Decomposition