United States Department of Transportation
i
Structural evaluation of LIC-310-0396 and FAY-35-17-6.82 box beams with advanced strand deterioration : draft final report – phase II.
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2011-09-01
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[PDF-13.07 MB]
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Edition:Draft final report - phase II.
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Abstract:This report describes the results from the testing of a full scale three span 43 year old adjacent prestressed concrete box beam bridge. This research is the second phase of the overall project entitled “Structural Evaluation of LIC-310-0396 Box Beams with Advanced Strand Deterioration” (State Job #134381). The first phase involved the forensic study and destructive testing of damaged individual beams removed from a similar type of bridge and described in the Interim - Phase I report. The results of Phase I showed the differences in behavior of the damaged beams on an individual basis.
However, these beams do not exist in bridges as single members. Unfortunately, the research does not currently provide experimental results for the complete adjacent box beam bridge system behavior. The evaluation of the behavior of the complete bridge system is critical for several reasons. The first reason is related to the robustness of the structural system for adjacent box beam bridges. For typical deck and girder bridges, the girders are spaced at distances of 6-9 feet (1.8-2.7m) with the bridge deck spanning in between the girders. For adjacent box beam bridges, the beams are placed adjacent to each other and tied together through shear keys as well as transverse tie rods. This adjacent placement causes a significant difference in the behavior of the beams in the bridge system compared to an individual beam. Though design standards provide analytical procedures to determine how loading transfers between the various beams, experimental evidence of these procedures is limited. In addition, determining how loads transfer in the beams of this structural system when members are damaged from deterioration does not exist analytically or experimentally. Typically, evaluation of damaged members are done assuming loads distribute to them as if they are not damaged.
This lack of analytical and experimental verification on the behavior of damaged prestressed box beam bridge systems is related to economics. An overly conservative approach to evaluating a bridge based on individual member capacity and undamaged load distribution behavior may lead to premature load restriction of the bridge, closing of the bridge, or replacement of the bridge. In addition, replacement of a bridge may be considered necessary when in fact a more economical solution may be repair of the bridge to extend its service life. Finally, not completely understanding the behavior of the bridge system compared to individual member behavior could lead to unexpected premature failure leading to damage of public property, personal injury, or worse. It has been noted that during removal of some damaged beams, collapse of the beams under their own weight have occurred once shear keys and transverse ties have been cut. If such as condition occurred in an operational bridge and went unnoticed, the consequences could be disastrous.
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