Wheel Load Distributions in Multi-Cell Box Girder Bridges

Although a simplified girder-line analysis is permitted by the 1998 AASHTO LRFD Bridge Design Specifications for the design of highway bridges in the US, fairly tight constraints are imposed on a number of important design parameters. For the case of box-girder bridges, which are a common type of bridges in California, the AASHTO LRFD Specifications imposes limitations on the curvature of the bridge, variation of deck-width, skew of bridge support, girder spacing etc. More specifically, the simplified 2D girder-line analysis is limited to bridges with:

  • Constant Deck Width
  • Number of Girders Great Than 4
  • Parallel Girders of Approximately Equal Stiffness
  • Plan Curvature Less Than 12 Degrees

For bridges with parameters outside of these constraints, design of such structures requires a more refined 3D analysis, either by finite element or grillage analysis. The objective of this project is to conduct a parametric study to examine the limitations imposed by the current AASHTO LRFD Specifications and determine if these limitations can be broadened for typical bridge geometry in California. Preliminary results indicated that the current AASHTO LRFD Specifications is conservative with respect to the distribution of bending moments and shear forces to individual girders, and constraints imposed by the Specifications can be extended.

Key publications

  • Song, Shin-Tai, Y. H. Chai and Susan E. Hida (2003), “Live Load Distribution Factors for Concrete Box-Girder Bridges”, Journal of Bridge Engineering, ASCE, Vol. 8, No. 5, pp. 273-280.

For a PowerPoint presentation of the project, click here.

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