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Fatigue Prone Steel Bridge Details: Investigation and Recommended Repairs
  • Published Date:
    2004-05-01
  • Language:
    English
Filetype[PDF-3.09 MB]


Details:
  • Corporate Contributors:
  • Publication/ Report Number:
    K-TRAN: KU-99-2
  • Resource Type:
  • TRIS Online Accession Number:
    01536582
  • Edition:
    Final Report
  • Format:
  • Abstract:
    Development of fatigue cracking has led to severe structural deficiency in many of the Kansas Department of Transportation’s (KDOT) welded steel bridges. In most circumstances, cracks were found to have developed at the connections of transverse structural members and longitudinal girders due to out-of-plane distortion. Procedures for determination of secondary stresses are not addressed by the current bridge design or rating specifications, since the details subjected to distortion-induced fatigue are often confined to highly localized regions and their corresponding stress fields are difficult to predict using conventional design or analysis approaches. This study presents the application of finite element methods for evaluation of out-of-plane fatigue behavior and recommendation of appropriate retrofit. Through proper modeling of the interaction between longitudinal girders and transverse structural members, causes of distortion-induced cracking were determined and different repair options were assessed. The central focus of the research is the case studies of five KDOT bridges with typical superstructure types and cracking scenarios. To link the global structural behavior under truck loading to the local stress concentration of crack prone details, a two-level finite element modeling approach was employed during the investigations. Both modeling procedures successfully determined the stress magnitude and distribution caused by out-of-plane distortion, and at the same time minimized the computation effort as well. Results obtained from the case studies verified crack severity observed in the field, helped identify potential crack locations, and suggested repair solutions to extend the bridges’ life. The overall repair method proposed for these four bridges is to stiffen the web gaps by welding or bolting the connection plates to girder flanges. The web gap regions should be able to withstand unlimited number of load cycles once the repair is carried out. The repair method proposed for the fifth bridge is to partially cut short the connection plate and reweld the crack. This repair is expected to provide a minimum remaining service life of fifteen years. The finite element modeling procedures used in this research effectively interpreted the out-of-plane fatigue behavior and crack growth characteristics, and provided guidance for future retrofit and field test implementations. The same analytical procedures can be extended to the study of other bridges as an alternative to experimental testing. It is recommended that this approach be included in the future update of AASHTO Guide Specifications for Fatigue Evaluation of Existing Steel Bridges as a method for evaluation of distortion-induced fatigue.

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