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

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. A variety of parameters were considered in the investigation, including skew angle and girder geometry. The skew angles that were considered varied from 0 degrees (normal supports) to 45 degrees. The geometry of the girder cross-sections ranged from doubly symmetric rolled sections to singly symmetric plate girders. The number of intermediate braces along the girder length was varied as well as the brace orientation relative to the girder axes. Two brace orientations were considered for each skew angle: parallel to the skewed supports and normal to the girder line. In addition to determining the general bracing requirements, improved bracing details were also considered in the study. Details are proposed that will reduce the brace forces induced from truck traffic. In addition, bracing systems that will reduce the number of cross-frames or diaphragms are proposed. Reducing the number of braces will make the bridges easier to inspect since there will be fewer fatigue-prone details.

  • Corporate Authors:

    University of Houston

    Department of Civil and Environmental Engineering, 4800 Calhoun Road
    Houston, TX  United States  77204-4003

    Texas Department of Transportation

    Research and Technology Implementation Office, P.O. Box 5080
    Austin, TX  United States  78763-5080

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Helwig, Todd A
    • Wang, Liqun
  • Publication Date: 2003-7-25


  • English

Media Info

  • Media Type: Print
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 238p

Subject/Index Terms

Filing Info

  • Accession Number: 01000942
  • Record Type: Publication
  • Report/Paper Numbers: Research Report 1772-1
  • Contract Numbers: Research Study 0-1772
  • Created Date: Jun 15 2005 11:06AM