United States Department of Transportation
i
Development of Quality Assurance and Quality Control System for Post Tensioned Segmental Bridges in Florida: Case of Ringling Bridge – Phase II
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2016-12-01
[PDF-48.62 MB]
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Edition:April 2017 - December 2018
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Abstract:The failure of two external post-tensioned (PT) tendons in the Ringling bridge was caused by corrosion of strands in deficient grout conditions. This prompted a thorough inspection of the tendons, as a result of which, fifteen other PT tendons were replaced in 2011-2012. Despite extensive repair work, practical limitations and technical constrains did not allow a thorough assessment of corrosion activity. An alternative assessment using nondestructive testing was desired to validate the corrosion activity and deficient grout. As part of Phase I of the project, NDT Corporation and Tokyo Rope Inc. successfully demonstrated their capabilities on blind mockup specimens using ultrasonic/sonic testing (UST) and magnetic main flux method (MMFM), respectively. During Phase II, these two testing companies were selected to carry out testing on Ringling bridge. Florida International University (FIU) provided support for on-site testing and independently evaluated the efficiency and effectiveness of these technologies. The UST company (USTC) carried out testing on the tendons located in the center cell of Ringling bridge using ultrasonic/sonic method to detect grout anomalies. The full length of tendon, including low horizontal, inclined, and high points, were tested for all spans. The MMFM testing company (MTC) carried out testing on inclined and high points of all tendons in the center cell (including additional tendons in Span 8 and Span 9) using the MMFM to detect steel strand loss. A total of nine sites were selected for tendon condition and nondestructive evaluation results verification which was carried out by Concorr FL. Of the four test sites recommended by MTC, site 1 and site 4 showed strong positive correlation with severe strand corrosion in the former and large embedded steel debris in the latter. MTC testing at sites 2 and 5a gave indication of cross-section loss, but tendon openings revealed clean strands in predominantly normal hardened grout. The verification of four locations recommended by USTC for grout anomaly did not indicate the anomalous grout conditions (voids, soft grout, and segregation). However, UST did give differentiation in through duct and circumferential resonant frequencies, indicating grout anomalies such as circumferential cracking. USTC requires more refinement of the data to characterize anomalous grout.
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