United States Department of Transportation
i
Design and Performance of Highly Skewed Deck Girder Bridges
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2018-05-01
[PDF-20.31 MB]
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Abstract:High skew alters load paths and creates unique performance problems. Acute corner deck cracking, bridge racking, overloading or uplifting at bearings, changes in shear and moment reactions can result due to live or thermal loads. This project investigates the performance of bridges in Wisconsin with high skew to identify limits for simplified analysis methods, to evaluate and recommend design details and practices that can mitigate negative impacts of skew on decks and bearings. A literature review, including review of practices in other states, was conducted. Selected bridges were inspected to identify problems unique to skew. One prestressed concrete and one steel girder were tested in-situ to collect data that can validate finite element analyses. Long term (1-year) data were collected on the prestressed concrete bridge. 2-D analyses validated with test data were run to evaluate American Association of State Highway Transportation (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications girder-line analyses for bridges with varying geometry and details. Analyses were also run to understand displacements and stresses under long term loading. Bridge inspections showed that not all bridges with skew have the problems to the same extent. Although skew increased maximum skew and decreased maximum moments, AASHTO specifications with Wisconsin Department of Transportation (WisDOT) exceptions were able to predict load distribution, albeit with minimal safety margin for some cases. Bridges should be designed to accommodate racking and expansion joint displacements, which can be calculated from longitudinal displacements using geometry. Using mixed bearings over a single pier significantly reduces bridge horizontal displacements and helps control deck cracking. Restraint of deck through full-depth end diaphragms, laterally restrained bearings, or additional reinforcement are expected to worsen deck cracking.
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