Live Load Distribution Factors for Straight Steel I-Girder Bridges

The current American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications (BDS) Article 4.6.2.2.2 provides approximate live load distribution factors (LLDFs) for line girder analysis of steel I-girder bridges and other beam-slab bridge types. Some of these provisions and specifically Article 4.6.2.2.2d, which covers LLDFs for exterior girders, are based on limited research, and various designers and owners have questioned their accuracy. The LLDFs in Tables 4.6.2.2.2b-1 and 4.6.2.2.2d-1 were developed assuming the presence of only end cross-frames and ignoring parapet stiffness. In addition, recent innovations in steel I-girder bridge design are facilitating the use of “lean-on bracing” framing systems on straight bridges with or without skew, which feature far fewer diaphragms or cross-frames than were traditionally used. Thus, the applicability of current AASHTO provisions is unknown. Research is needed to investigate the appropriateness of the current LLDFs for straight steel I-girder bridges using either traditional framing or lean-on bracing framing. OBJECTIVE: The objective of this research is to evaluate the accuracy of the moment and shear LLDFs provisions for girders in straight steel I-girder bridges with composite concrete deck when using line girder analysis methods.

• Record URL:
  • http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=5866
• Supplemental Notes:
  • Contract to a Performing Organization has not yet been awarded.

Language

• English

Project

• Funding: $750,000
• Contract Numbers:

  Project 12-131

• Sponsor Organizations:

  National Cooperative Highway Research Program

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

  American Association of State Highway and Transportation Officials (AASHTO)

  444 North Capitol Street, NW
  Washington, DC  United States  20001

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Project Managers:

  Abu-Hawash, Ahmad

• Start Date: 20260113
• Expected Completion Date: 0
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Girder bridges; Live loads; Load transfer; Mechanical fatigue; Steel bridges
• Identifier Terms: AASHTO LRFD Bridge Design Specifications
• Subject Areas: Bridges and other structures; Design; Highways;

Filing Info

• Accession Number: 01956835
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 12-131
• Files: TRB, RIP
• Created Date: May 29 2025 1:11PM