Graduate Thesis Or Dissertation
 

Application of Titanium Alloy Bars for Strengthening Reinforced Concrete Bridge Girders in Flexure

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  • Structurally efficient and cost-effective solutions are needed to extend the service-life of deficient and aging highway infrastructure around the world. One critical need is to increase the flexural strength of older reinforced concrete (RC) structures to carry heavier and more frequent loads. Titanium alloy bars (TiAB) offer a new opportunity to strengthen such existing structures that has not previously been explored. Research on strengthening existing civil infrastructure using titanium alloy bars was undertaken in the laboratory through tests of full-scale RC bridge girders using two alternative strengthening techniques for flexure: near-surface mounting (NSM) and external unbonded reinforcement. The goals of this research were to determine fatigue effects and environmental durability of NSM TiABs and to investigate the behavior of RC girders strengthened with external unbonded TiAB reinforcement. The NSM retrofit technique involved cutting grooves into the concrete surface and bonding specially fabricated titanium alloy bars inside the grooves using structural epoxy. Original investigation of this novel technique was undertaken during previous research at Oregon State University and has since been installed on an existing bridge in the USA over a major interstate highway. However, the effects of long-term fatigue loading and environmental exposure on this technique are unknown and thus were investigated for this study by testing a similar retrofitted, full-scale RC girder as in the prior work but subjected to simultaneous fatigue and freeze-thaw cycles. It was determined that no significant changes in strength or stiffness were observed due to the combined fatigue and environmental effects compared to the companion specimen. The external unbonded reinforcement technique requires only drilling holes into the girder web. Smooth as-rolled TiABs with 90o hooks fabricated on the ends are not bonded along the length of the girder. To attach the bars to the girder, the hooks were anchored using one of two methods: epoxy bonded in the hook holes, or inserted entirely through the web and held in place with prestressing chucks. To investigate the effectiveness of the technique, two full-scale concrete girders were strengthened in the laboratory. Compared to a numerically modeled control specimen, strengthened girders exhibited significant increases in both ultimate strength and ductility with the prestressing chuck anchoring method showing considerable improvement over the epoxied hooks. However, due to the relatively low stiffness which results in large displacements and wide cracks, the technique is more suited for temporary strengthening necessitating rapid installation, such as after a seismic event, vehicle impact, or other such event.
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