Revisit of AASHTO Effective Flange-Width Provisions for Box Girders

The nonuniform normal stress distribution along the flange of thin-walled flexural members, such as box girders, is recognized as shear lag effects. Effective flange width is widely used to consider shear lag effects in bridge design. The existing provisions for effective flange width in AASHTO LRFD Specifications can be unconservative compared with this study and other design regulations worldwide. An energy-based variation analysis was used in the study to evaluate the AASHTO provisions. With extensive parametric studies, equations were proposed to calculate the effective flange width for box girders. The new provisions consider the critical factors for the shear lag behavior: geometry of the girder, loading pattern, material properties, and the existence of longitudinal stiffeners.

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