Advanced bridge safety initiative : investigation of floor beam performance in three steel through-truss bridges - task 7.
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2014-08-01
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Abstract:The Advanced Structures and Composites Center at the University of Maine (UMaine) performed live load testing
and rating adjustment factor analysis for three truss bridges. The Maine Department of Transportation (DOT)
indicated that the floor beams are not sufficient for carrying the legal loads for these bridges. Each bridge is a steel
through-truss bridge with floor beams, stringers and a variable depth concrete slab that was not designed to be
composite with the steel framing. The bridges were all located in Maine in Brownville, Chester and T-3 Indian
Purchase. Live load testing was conducted on April 8th, April 10th and April 15th, 2014 by UMaine with assistance
from Maine DOT personnel to evaluate the performance of typical floor beams. Stringers were considered to be of
secondary concern to the Maine DOT, and were not heavily instrumented.
The strain measurements were consistent, and the results appear reliable. Measured floor beam strains were less than
expected based on a lever rule analysis for live load distribution. If the MaineDOT agrees with our assessment, a
conventional, lever rule load rating of the floor beams for these three structures that accounts for the condition of the
floor beams including section losses must be completed. The rating factors determined from these analyses can then
be increased by the values of K reported. Any existing cracking near copes or connections and remaining fatigue life
have not been considered as part of this analysis, and should also be considered given the age of these structures.
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