Cross Frame Stiffness Study by Using Full Size Laboratory Test and Computer Models

Cross frames are critical bracing elements for the stability of steel bridge systems. They help plate girders in resisting lateral torsional buckling and contribute to live load distribution. In curved bridges, cross frames serve as the primary structural members in resisting torsion generated by the eccentric loads. Therefore, accurately estimating the stiffness and strength of cross frames is important in bridge design. A Texas Department of Transportation (TxDOT) sponsored research project at the University of Texas at Austin is focused on improving the behavior of steel bridge cross frames. Previous studies have shown the effectiveness of a single diagonal tubular cross frame system in stabilizing plate girder structures. However, the stiffness and ultimate strength of this type of cross frame has not been thoroughly characterized. Also, connection details have not been considered. This paper documents the results of a study on the torsional stiffness of full size cross frame systems. Both conventional and newly proposed designs are being tested to establish the actual torsional stiffness of the cross frames. Furthermore, a comparison is made using different computer models to evaluate the stiffness.

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