Shear strengthening reinforced concrete bridge girders using near-surface mounted titanium alloy bars Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/73666692w

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  • Aging and deficient infrastructure has become a major problem throughout the world. This is particularly evident in the case of reinforced concrete (RC) bridges. The cost of replacing these bridges is often prohibitive, thus engineers must find ways to strengthen them. Many older RC bridges predate the modern understanding of shear behavior in girders, and were built with insufficient internal transverse reinforcement. These bridge girders often exhibit diagonal-tension cracks in the high-shear zones near the supports. One method commonly used to strengthen RC bridge girders is called near-surface mounting (NSM), which involves cutting vertical grooves into the concrete and adhesively bonding supplemental reinforcing. Although this method was first developed for use with steel bars, it is now most commonly implemented using carbon fiber rods, as steel bars near the concrete surface can corrode. The objective of this research was to investigate the use of titanium alloy bars as a viable alternative to steel and carbon fiber for NSM shear strengthening applications. The titanium alloy has several advantages over the other materials. It is insensitive to corrosion, it can be bent to provide mechanical anchorages at the ends, and it exhibits high strength and elongation on par with conventional reinforcing steel. These properties allow the use of small diameter bars, which can reduce installation costs. For the research program, seven realistically proportioned T-shaped reinforced concrete girders were constructed, and then strengthened with NSM titanium alloy bars. The specimens were tested to failure under four-point bending. Both positive and negative moment sections were investigated. Two commercially available epoxies were used to bond the titanium alloy bars. The test results showed that the titanium alloy bars yielded prior to failure. The hooks maintained the force in the bars even after the loss of bond along the length of the titanium alloy bars. Two specimens with different epoxies were subjected to simultaneously applied high-cycle fatigue and freeze-thaw cycles before being tested to failure. One of the specimens exhibited reduced strength, indicating the importance of proper selection of the epoxy used to bond the titanium alloy bars to the concrete. The experimental results were compared with code models, and it was determined that the present design specifications can conservatively be used to predict the strength of RC bridge girders strengthened for shear using NSM titanium alloy bars.
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