Static and creep response of RC beams strengthened with CFRP
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI--COLUMBIA AT REQUEST OF AUTHOR.] The use of carbon fiber reinforced polymers (CFRP) for strengthening and retrofit of existing reinforced concrete members has been proven to be effective in improving their structural performance. Although existing research studied the behavior of concrete structural element strengthened/retrofitted with CFRP sheets, there is still a need to improve the understanding of the behavior of reinforced concrete (RC) continuous beams strengthened/retrofitted with different (CFRP) configuration under negative moments. In addition, the effects of sustained loading and environmental impact on the performance of the strengthened beams, CFRP sheets, and their bond to concrete still need more investigation. Therefore, in this dissertation the short-term and long-term performance of reinforced concrete rectangular beams strengthening with CFRP was evaluated. In addition, the effect of CFRP U-wrap on the performance of RC beams was also studied under short and long-term loadings. The response of RC T-beams retrofitted with CFRP was also investigated in this dissertation under positive and negative curvature. The short-term static testing included beams under a controlled lab environment and other beams under outdoor environment for 18 months. The long-term testing included beams under controlled lab environment with sustained loads for 332 days. These beams were also tested to failure to evaluate their residual strength and stiffness after undergoing the sustained long-term loading. It was found that the use of the U-Wrap strips increases the effectiveness of the longitudinal reinforcement which leads to increase in the load carrying capacity of the strengthened beams. The strength of RC beams that had web steel reinforcement was not impacted as a results of exposure to outside weather for 18 months. Their strength was very similar to the beams that were left in the lab under controlled environment. However, the beam reinforced with longitudinal CFRP and CFRP U-wrap after exposure to external weather for 18 months had a strength 17 percent less than that of the same beam under no exposure. The beam with exposure failed by deponding of the U-wrap leading to premature failure of the beam compared to the beam with no exposure where the failure was controlled by rupture of the U-wrap. This indicates that the use of web steel reinforcement is more effective than using CFRP U-wrap. It was found that the residual strength of the long-term creep-tested beams was 5 to 18 [percent] lower than the strength of the short-term beams except for the steel over-reinforced beam. Whereas, the residual stiffness did not change significantly. However, the residual toughness was 22 [percent] to 64 [percent] of the toughness of the short-term beams due to creep damage. The web steel reinforcement played an important role in improving the overall performance and failure mode of the CFRP-RC beams.
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