Design and Performance of Highly Skewed Deck Girder Bridges
Diaz Arancibia, Mauricio
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Highly skewed deck girder bridges experience several performance problems. These stem from modified load paths that change girder load distribution, superstructure horizontal movements and deck diagonal cracking caused by long-term loading. This research was motivated by the need to understand and quantify the adverse effects of skew on load distribution and performance of bridges, and identify design details that can mitigate these effects. Skew related provisions of AASHTO LRFD Bridge Design Specifications and several Depts. of Transportation were reviewed. Field inspections were conducted on low and high skew prestressed concrete and steel girder bridges. One prestressed concrete and one steel girder bridge with high skew were load tested in the field. The prestressed concrete bridge was also monitored for a year for long-term effects. These efforts aimed to reveal the effects of existing deck cracks on load distribution under truck loading, and horizontal movements and deck cracking behavior under long-term loading. Validated 1-3D finite element models were used to explore skew angle effects on load distribution, horizontal movements, fixed bearing forces, and deck cracking.The research showed that not all skewed bridges have performance problems to the same degree, emphasizing the importance of other bridge details and geometry. Increasing skew amplified horizontal movements, fixed bearing forces, and deck cracking under long-term loading. The level of model refinement needed to reach adequate safety margins for girder load distribution, horizontal movement and fixed bearing force was revealed. A truss analogy model was proposed for preliminary design of expansion bearings. Experimental and analytical results showed that using mixed bearing arrangements over piers was effective in controlling excessive thermally induced transverse bearing movements. Fixed bearing forces may be reduced by introducing non-composite action between deck and girders. Details that may improve deck cracking were bridge ends without diaphragms and laterally restrained expansion bearings. Increasing deck reinforcement, and/or orienting it along the skew aggravate cracking.