Research for AASHTO Standing Committee on Highways. Task 415. Proposed AASHTO Guidelines for Bottom Flange Limits of Steel Box Girders

Steel box girder bridges are being used on a more and more widespread basis as they represent an alternative to steel I-girder bridges. Designers can be tempted to specify very thin/slender bottom flanges for steel box girders in positive moment regions (where the bottom flange is in tension). However, specifying too thin or too slender of a bottom flange could result in problems during fabrication, transportation, erection, or future inspection/maintenance, and potential strength and fatigue issues. Currently there is no consensus on minimum thickness and maximum slenderness limits for steel box girder bottom flanges. Industry recommendations on minimum bottom flange thicknesses vary, but are generally in the range of ¾” to 1”. Industry recommendations for bottom flange width to thickness (b/t) slenderness ratios also vary, generally over a range from 80 to 135. Since there are currently no limits in the AASHTO LRFD Bridge Design specifications, designs with even higher slenderness ratios are not precluded. The objective of this project was to propose AASHTO guidelines for the minimum thickness and maximum slenderness limits for steel box girder bottom flanges to (1) minimize issues during fabrication, handling, and erection; and (2) enhance the long-term performance of steel box girders.


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  • Status: Completed
  • Funding: $80000
  • Contract Numbers:

    Project 20-07, Task 415

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Dekelbab, Waseem

  • Performing Organizations:

    Georgia Tech Research Corporation

    505 Tenth Street
    Atlanta, GA  United States  30332-0420
  • Principal Investigators:

    White, Donald

  • Start Date: 20180809
  • Expected Completion Date: 20190708
  • Actual Completion Date: 20190708

Subject/Index Terms

Filing Info

  • Accession Number: 01669530
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 20-07, Task 415
  • Files: TRB, RIP
  • Created Date: May 21 2018 8:56PM