Graduate Thesis Or Dissertation
 

Flexural anchorage performance and strengthening on negative moment regions using near-surface mounted retrofitting in reinforced concrete bridge girders

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  • Large numbers of reinforced concrete deck girder (RCDG) bridges were built during the highway infrastructure boom of the 1950's. The advent of standardized deformed steel reinforcing bars during this time allowed for straight bar terminations in flexural tension regions. Designers of the time terminated reinforcing bars where they were no longer required by calculation and did not account for additional demands from the combination of shear and flexure. The design provisions of the time allowed higher shear stresses in the concrete than allowed in standards today which reduced the required quantity of transverse reinforcing steel. In addition, heavier trucks and higher traffic volumes on roadways today have greatly increased the service loading on these bridges. Engineers evaluating these older RCDG bridges often determine unsatisfactory load ratings due to flexural anchorage deficiencies in the girders, especially when the influence of shear is considered. These deficiencies result from inadequate capacity compared to current design standards due to poor cutoff details used in the initial design. Strengthening methods are necessary because comprehensive replacements of the large number of bridges are not economically feasible. Experimental research was conducted to evaluate the behavior of poorly detailed flexural anchorages and to develop methods to strengthen them. Realistic vintage girder specimens were constructed, retrofitted, instrumented, and tested to failure. The specimens reported in this thesis were full-scale inverted-T (IT) beams. Some of the specimens contained straight bar terminations crossing a preformed diagonal crack in the flexural tension region to investigate the influence of shear on the retrofit schemes. Instrumentation focused on measurement of the reinforcing steel stresses surrounding the diagonal crack and along the development length of the cutoff bars. Using results of past research to quantify the behavior of girders with straight-bar flexural anchorages in flexural tension regions, an innovative strengthening technique was developed using either near-surface mounted (NSM) stainless steel or titanium. Results from the NSM strengthening technique demonstrated the ability to delay or prevent flexural anchorage failures, with increased deformation capacities and increased strengths from 17% to 39% over baseline specimens. To show the success of this research and the immediate need for strengthened flexural anchorages, this research has already been implemented on a bridge in Mosier, Oregon. This groundbreaking research is described in detail in Appendix F.
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