Hydrodynamic Uplift Forces on Submerged Bridge Decks during Bedform Migration

Abstract

Hydrodynamic forces, especially uplift forces, during a flood event are critical to the stability of bridge superstructures. This study focuses on the interaction between the migrating dunes, the scour depth beneath the deck, and the uplift force that fluctuates during bedform migration. Experimental results show that the fluctuation of uplift forces is closely related to the arrival of dune crests and troughs, which periodically alter the approach flow behavior. The fluctuation becomes particularly apparent for partially submerged decks, for which the intermittent overtopping phenomenon plays an essential role in producing vertical forces with varying directions. In contrast to previous studies using fixed plane beds, positive uplift forces may occur in this study for some partially submerged decks, which poses an additional risk to the superstructure. New lift coefficient equations are proposed to take the effect of migrating dunes into consideration and enhance the safety margin in design for highly dynamic fluvial environments.