United States Department of Transportation
i
Finite Element Analysis of Fatigue Prone Details of the Tuttle Creek Bridge
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2007-11-01
[PDF-9.79 MB]
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TRIS Online Accession Number:01088248
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Abstract:Many older steel girder bridges exhibit distortion-induced fatigue cracking at the cross-frame to girder connections. In a two-girder bridge like the Tuttle Creek Bridge there are no redundant load paths and this problem is of even greater concern. The primary girders of the bridge structure are fatigue critical elements and even when such cracks are relatively small they must be examined extensively. The Tuttle Creek Bridge, built in 1962, developed distortion-induced fatigue cracks in the web gap region. The crack prevention repairs of 1986 were not effective and continued crack growth was observed. The bridge was again repaired recently in the summer of 2005. A finite element study is performed in this study for a typical intermediate girder span, to characterize the behavior of fatigue critical details and to evaluate the effectiveness of the newly installed retrofits. A dual-level finite element analysis was performed using macro-level models of the entire bridge structure and micro-level models of some portions of the bridge under investigation. The finite element procedure was found to be efficient and accurate. The models were calibrated using field strain data obtained from two field tests done before and after the retrofits. The analytical results were in good agreement with the measured field data. The analysis shows that the top flange web gap region is the most susceptible to distortion-induced fatigue. The study successfully explains the observed crack patterns on the bridge. The study indicates a significant reduction in web gap stresses after the retrofit. The retrofit also reduces stresses in the gusset plate region and eliminates the stress concentration near the weld terminations. Based upon the most critical detail and assuming that the traffic volume doubles from the present AADT of 65, the service life of the bridge is estimated to be over one hundred years.
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