Thesis
LOW-CYCLE FATIGUE BEHAVIOR OF MODERN AND HISTORIC GRADE 40 REINFORCING STEEL BARS
Washington State University
Master of Science (MS), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004480
Handle:
https://hdl.handle.net/2376/125072
Abstract
This research evaluated the predictability of the fatigue behavior of modern and historic grade 40 reinforcement when subjected to different strain histories and to characterize differences observed. While several previous studies have investigated the low-cycle fatigue behavior of grade 40 reinforcing steel using constant amplitude cycles with zero mean strain, existing research was minimal for tests with variable amplitude loading and strain histories with positive mean strain that would be characteristic of the strain history for reinforcement bars in reinforced concrete columns subjected to cyclic loads. First, sixteen constant amplitude cyclic tests were conducted to calibrate the parameters of the Koh-Stephens fatigue relationship. The calibrated M and n parameters were calculated to be 0.15 and -0.38 for the modern grade 40 reinforcement, respectively, and 0.07 and -0.45 for the historic grade 40 reinforcement, respectively. Then, twelve variable amplitude cyclic tests were conducted. The damage accumulated over the variable amplitude strain history was tracked using the Miner rule to predict fatigue fracture. Results showed high variability, with coefficient of variations above 0.25 for almost all specimen sets, and high sensitivity to model parameters. Electron backscatter diffraction scans were taken of both the modern and historic grade 40 reinforcement to determine if differences in metallurgy could explain the variability. The electron scans determined that the historic reinforcement, recovered through demolition of 70-year-old in-service bridges, had greater previous strain deformation than the modern virgin-steel bars. It was also found that the grain size of the virgin steel bars was more consistent than the historic bars. These two findings together help explain some of the high variability in the testing data. In conclusion, this study determined that modern reinforcement likely has between 50% and 100% more elongation at fracture and greater cyclic fatigue life than historic bars. This should be considered when evaluating older in-service bridges for retrofit and comparing retrofit strategies using modern experimental tests, as the reinforcement in modern tests likely has greater fatigue life. Additionally, the study identified additional research questions aimed at increasing the predictability of fatigue fracture of reinforcement subjected to variable strain histories generated from earthquake ground motions.
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Details
- Title
- LOW-CYCLE FATIGUE BEHAVIOR OF MODERN AND HISTORIC GRADE 40 REINFORCING STEEL BARS
- Creators
- Zach John Quesnel
- Contributors
- Adam Phillips (Advisor)Christopher Motter (Committee Member)Don Bender (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Civil and Environmental Engineering, Department of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 98
- Identifiers
- 99900882138401842
- Language
- English
- Resource Type
- Thesis