Comparative Evaluation of Flexural Strengthening and Bond Performance of Reinforced-Concrete Beams Strengthened with Near-Surface-Mounted Titanium-Alloy Straight Bars

Strengthening reinforced-concrete (RC) members using near-surface-mounted (NSM) titanium-alloy bars (TiABs) has become an emerging method to extend the service life of RC structures. Current design and construction guidance for strengthening existing RC structures with this method is limited to the usage of TiAB with hooked ends, which can be challenging for structures where accommodating hooks is impractical. To evaluate an alternative mounting method, experimental work was performed in this study to investigate the flexural behavior of RC beams strengthened with NSM straight TiAB (without end hooks) and determine their bond strength for development length calculations. Five RC beams strengthened with NSM TiAB having TiAB bonded lengths were tested and compared against an unstrengthened control specimen. The test results indicate that beams strengthened with straight TiABs can achieve increased load capacity, provided that sufficient bond length is provided. Specimens with sufficient bond length demonstrated performance comparable to those strengthened with hooked TiABs, achieving yielding in both the steel reinforcement and the TiAB. An average bond strength of 0.5 ksi for straight TiABs is recommended when performing development length calculations. Additionally, this study presents guidelines and construction procedures for the practical application of NSM straight TiABs.