Flow distortion recorded by sonic anemometers on a long-span bridge: Towards a better modelling of the dynamic wind load in full-scale

Abstract

The turbulent wind field around a suspension bridge deck is studied using eleven months of full-scale records from sonic anemometers mounted above the girder. Using the mean and turbulent velocity characteristics, we demonstrate that the bridge structure can significantly distort the flow. More precisely, the friction velocity, the variance of the fluctuating vertical velocity and the mean wind incidence angle are underestimated on the downstream side of the deck. The local topography is also found to influence the flow in a non-negligible way, such that turbulence characteristics differ significantly from those observed in flat and homogeneous terrains. For a hexagonal girder with a width to height ratio B/H approximate to 4.5, deck-induced flow distortion is still observed on the downwind side of the girder at a height above the road equal to 3.6H. This further supports the idea that wind measurements from a suspension bridge should rely on anemometers on both sides of the deck to mitigate flow distortion. The improved flow description combined with high-resolution acceleration records of the deck provides a simulation of the wind-induced response of the bridge with a level of accuracy that is rarely achieved in full-scale. In particular, the limits of a wind model based on flat terrain assumption as well as the limits of the strip theory are highlighted by the recorded data and the improved modelling of the bridge buffeting response