Evaluation of flange bending stresses in non-composite steel I-girder bridges during construction

Abstract

Exterior girders undergo direct torsional effects applied by deck forming brackets during construction. During this phase while these members are not composite, these effects are counteracted by internal lateral forces developed primarily in the flanges that modify the major-axis bending stresses produced by vertical loads. In curved and skewed bridges, additional lateral flange bending is introduced due to the eccentricity of the loads with respect to the supports and differential displacements. In this paper, approximate equations are proposed from a parametric study to estimate the lateral flange bending in continuous straight, skewed and curved bridges during the deck placement. The proposed equations were found to be less conservative than AASHTO approximate equations. For curved bridges, the major-axis bending was also approximated in terms of the curvature. The results showed that the variable that most affects the limit states for constructibility is the curvature, followed by the cross-frame spacing to a lesser degree. Conversely, for the girders evaluated in this work through the range of parameters studied, the limit states were not found to be sensitive to skew angle.

Keywords:

• steel I-girder bridges
• construction loads
• lateral flange bending
• finite-element analysis