Analysis Tools and Rapid Screening Data for Distortional Fatigue in Steel Bridge Girders


Evan Berglund, Arturo Schultz

November 2001

Report no. MnDOT 2002-06

Fatigue Cracking often occurs in composite bridges with unstiffened girder web gaps at the ends of transverse stiffeners. In this project, researchers sought to better understand bridge diaphragm deflection behavior and advance the ability to estimate web gap distortional stress. Trends from the parametric studies led to general observations that may assist in identifying fatigue-prone bridges. Variables that influence diaphragm deflection behavior include girder spacing, bridge skew, span length, and deck thickness. Transverse load distribution properties appear to play the most significant role in determining the magnitude of differential deflection. Parameter study stress trends indicate that out-of-plane distortional stress in fatigue prone web gaps primarily depends on web gap properties, bridge span length, and angle of skew. Differential deflection and web gap dimension trends apply to a varied spectrum of bridge configurations. The research resulted in a method to assess bridge girder differential deflection and distortional stress in actual steel bridges without complex analysis and modeling. Proposed procedures for evaluating out-of-plane stress should prove practical and aid in screening, identifying, and assessing bridges vulnerable to distortion -induced fatigue cracking.

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