Automated Screening Tool for the Stability of Highway Bridges Subject to Scour
Type of DegreeThesis
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Most bridges in Alabama that are over shallow bodies of water, including small creeks, wetlands, and marshes, were designed so that the bridge superstructure is supported on pile bents. During major flood events, excessive scour can occur at these bridge bent sites. Scour is the washing away of streambed material by the water channel flow. Hundreds of Alabama’s bridges were designed and constructed without recognizing the impact of scour events on the bridge piers. In lieu of this problem, the Alabama Department of Transportation (ALDOT) is currently assessing the scour susceptibility of its bridges, including an evaluation of the structural stability of these bridges for an estimated flood/scour event. Phase I research work determined that the development of a “screening tool” was technically feasible, the primary parameters that scour susceptibility depends on were identified, and it was verified that these parameters were in ALDOT’s databases, or could be estimated reasonably. In Phase II, a “screening tool” was developed to assess the adequacy of bridge pile bents for an estimated flood/scour event, and a user’s guide that explained the proper use of the tool when evaluating the structural stability of the pile bents was created. The objective of the Phase III work was to expand, refine, and automate the “screening tool” developed in the previous phases. This report focuses on the automation of the screening tool. Visual Basic Studio 2005 was the software package (chosen in agreement with ALDOT engineers) used to automate the ST. The ST is a stand-alone computer program in which ALDOT engineers input bridge/site parameter values, and the program evaluates the stability of a critical pile or bent, or a set of bents, and outputs results regarding the adequacy of the bridge's stability. The ST evaluates the four most critical failure modes, which were identified in Phases I and II as plunging, kick-out, buckling, and pushover failures. Tier-2 screening refinements and expansions, introduced in a sister Phase III report, were also included in the automation of the ST.