Brace Stiffness Quantification for Lean-on Bracing

Cross-frames are critical for the stability of steel bridges during construction and play an important role in completed bridges. Historically, brace locations have been regions of fatigue concerns, and each brace requires significant handling and processing during fabrication. The braces represent one of the most expensive bridge components per unit weight. Therefore, there are major benefits to minimizing the number of cross-frames in a bridge in terms of economics and structural performance. In the application of lean-on bracing concepts, select cross-frames are replaced in certain bracing lines with top and bottom struts, which allow a single cross-frame to brace several girders as a method of minimizing the number of cross-frames in a bridge. Lean-on concepts were developed for the Texas Department of Transportation (TxDOT) in the early 2000s. Previous studies developed design guidelines, but recent applications of lean-on bracing in TxDOT bridge designs demonstrated the need for improved efficiency and clarity. The primary focus of this paper is related to the stability stiffness and strength capacity of lean-on cross-frame lines. The impact of the number of cross-frames per bracing line, will be discussed in terms of stability implications. Future work will validate the approaches detailed in this paper to determine an expression for the stiffness and strength contribution of the torsional brace.

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