Influence of Bridge Piers on Velocity under Unsteady Flows

Abstract

It is reported that every year hundreds of bridges collapse due to the dynamic forces acting on the piers, particularly during floods and the scour around the foundations. Since the determination of the velocity distribution upstream of the pier is directly related to thisforce, it is important to predict the effect of a presence and diameter of a bridge pier on velocity and turbulence parameters. In this study, the time variation of point velocities in the stream-wise and vertical direction at a point upstream of a bridge pier was obtained under clear-water and unsteady flow conditions. The presence of the bridge pier causes the velocity profile to be steeper. The increase in pier diameter decreased the maximum stream-wise velocity whereas it increased the vertical velocity in the down flow directionparticularly near the bed. The turbulence intensity in stream-wise direction increases in the rising limb and decreases in the falling limb, more prominently near the bottom. The maximum percent reductions in the stream-wise velocities at peak flow were calculated as 6% and 11% for the small and big piers, respectively. The reduction in stream-wise velocity at peak flow increases with depth especially for the pier with greater diameter.

Keywords

• flood flow
• bridge pier
• velocity time series
• velocity profile