| 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.;This paper is organized into two primary parts. The first, entitled "Distortion-Induced Fatigue in Steel Bridges: Causes, Parameters, and Fixes" is a stand-alone article and was published in the conference proceedings of the American Society of Civil Engineers/Structural Engineering Institute (ASCE/SEI) Structures Congress, held in Orlando, Florida in May 2010. The second is entitled "Parametric Analysis of Cross Frame Configuration on Distortion-Induced Fatigue in Skewed Steel Bridges." The main body of the second portion is intended for future publication and therefore, supplementary material containing additional details of the investigation have been included in appendices and are separated by topic. |
