United States Department of Transportation
i
Flexural Steel Anchorage Performance at Diagonal Crack Locations [Dissertation]
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2010-04-29
[PDF-27.13 MB]
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Abstract:Large numbers of reinforced concrete deck girder bridges that were constructed during the interstate system expansion of the 1950s have developed diagonal cracking in the stems. Compared to the present AASHTO-LRFD standards, the provisions of the 1950s allowed for higher shear stress in the concrete, thus reducing the amount of transverse steel required. Further, service loading has increased over time. When load-rating these structures, the current design specification check of tension reinforcement anchorage often controls the capacity of these bridges. This check compares the applied tensile force in the reinforcement to the tensile force available based on the reinforcement development length. The tensile force demand is controlled by the load-induced moment and shear, the number of stirrups, and the diagonal crack angle. However, the crack angle considered in the design specification is commonly flatter then the angle of the vertically-oriented cracks generally noted in field inspections. The tensile force that can be developed in the flexural reinforcing steel depends on the diameter of the bar and the embedded length, however, little information is currently available regarding bond stresses developed with larger-diameter bars for full-size specimens in the presence of diagonal cracks. Experimental data from realistic full-size specimens with anchorage of flexural bars interacting with diagonal cracks would enhance ratings methods for evaluation of existing bridges. Ultimately, improved understanding of the response of these bridge girders can help maintain the operational safety and freight mobility of the transportation system, thereby allowing optional use of available resources for repair or replacement of truly deficient bridges.
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