Screening Tool to Assess Adequacy of Bridge Pile Bents during Extreme Flood/Scour Events

A common design/construction procedure for highway bridges in Alabama is the use of steel HP piles driven to a firm stratum with a length above ground up to the level of a concrete bent cap which supports the bridge superstructure. The use of three, four, five, or six such piles in a row with the two end piles battered are very common bridge pile bents. Because of the large number of bridges in the state and the tendency to use standardized designs with pile bent substructures, the Alabama Department of Transportation recently developed a “screening tool” to assist its engineers in assessing the adequacy of bridge pile bents for extreme flood/scour events. The evaluation procedure employed in the screening tool is presented in macro and microfloodchart form in this paper, and basically moves through the following sequence: (1) preliminary or general checks such as the bridge bent being located in water with scour possible, etc.; (2) checking the bent piles for possible “kick-out” or plunging failure; (3) checking the bent piles for buckling failure; and (4) checking the bent for transverse (transverse to the bridge centerline) pushover failure from combined gravity and flood water loadings. The screening tool is a dynamic tool and is currently being automated, expanded in capabilities, simplified, and improved.