Stability Bracing Requirements for Lean-on Systems

Lateral torsional buckling often controls the design of steel bridges during construction. The buckling resistance is affected by a number of factors, including the geometry of the girders and the spacing between braces. Steel bridges are commonly braced by cross-frames, which commonly consist of single-angle members. In bridges with complex geometry such as significant support skew, the installation and long-term maintenance of cross-frames are complicated due to the skewed geometry. Lean-on bracing concepts, which selectively remove cross-frames in place of utilizing only top and bottom struts are becoming an attractive design option. Lean-on bracing significantly improves the ease of installation during erection and can also reduce the fatigue demands on the braces. However, there are several questions regarding the stability bracing behavior of these systems. Recent research has shown that system behavior is greatly influenced by the implementation of lean-on bracing, but has not specifically addressed the impact of different lean-on bracing configurations on the stiffness and strength of these systems. This paper is focused on a methodology for quantifying the impact of configuration on lean-on bracing systems through the use of linear eigenvalue buckling and nonlinear imperfection analyses.

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