Trapezoidal steel box girder systems are frequently used in Texas for the construction of highway interchanges and elevated expressways in urban areas. Although these girder systems are widely used, there are a number of aspects about their behavior that are not well understood. Previous studies have been conducted on the boxes that have resulted in design expressions for some of the bracing systems that are used to improve the torsional response of the girders. However these studies were conducted on girders with radial supports and no external intermediate cross-frames. The effect of the skew angles and the external bracing on the internal bracing systems is not well understood. The focus of the research outlined in this dissertation has focused on the behavior of steel box girders with skewed supports. The effect of the skew angle and the external intermediate cross-frames on the girder behavior has been investigated through field monitoring and computational studies. The study has resulted in modifications to previous design expressions as well as recommended bracing details. A design methodology for external intermediate bracing has also been formulated.
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