Cross-Frame and Diaphragm Behavior for Steel Bridges with Skewed Supports: Fid-Bau Portal

Cross-Frame and Diaphragm Behavior for Steel Bridges with Skewed Supports

T. A. Helwig / L. Wang

Steel bridge girders are prone to buckling from construction loads during casting of the concrete for the composite deck. The buckling capacity of the steel girders can be increased by providing bracing at intermediate locations along the girder length. The intermediate bracing typically takes the form of cross-frames or diaphragms. Skewed supports occur when the supporting abutments for the girders are not normal to the girder line, but are instead offset by a skew angle. The skew angle may be required due to characteristics of intersecting roadways or due to the geological terrain. Fatigue cracks are commonly found around locations of cross-frames and diaphragms during routine maintenance inspections. These cracks form from large stress concentrations in the girder due to cross-frame and diaphragm forces induced by truck traffic on the bridge. This is particularly true for bridges with skewed supports. The objective of the research outlined in this report is to improve the understanding of the bracing behavior of cross frames and diaphragms in steel bridges with skewed supports. General bracing requirements are developed and new cross-frame and diaphragm details to minimize fatigue problems at bracing locations are proposed.