An Analytical Evaluation of Distortion-Induced Fatigue in Steel Bridges

Abstract

Multi-girder steel bridges designed prior to the mid-1980's, have developed cracks due to distortion-induced fatigue. An analytical evaluation was conducted to better understand the effects of bridge configurations and common retrofits on distortion-induced fatigue, as quantified by hot spot stress in web gap regions. Results are described herein and present relative distortion-induced fatigue susceptibility of multi-girder bridges with varied skew angle, cross frame spacing, bracing configuration, and cross frame stiffness as well as regions within each variation where cracking is most likely to occur. Performance of retrofit techniques was also compared and included positive attachment, a slotted connection stiffener, a back-up stiffener, and cross frame removal with each implemented both locally and globally. In addition, influence surfaces were generated and analyzed for three bridge configurations to better understand the relationship between load placement and distortion-induced fatigue related stresses. It is hoped that this research will benefit bridge engineers working to identify and extend the fatigue life of bridges susceptible to distortion-induced fatigue.