United States Department of Transportation
i
Corrosion Monitoring Research for City of New York Bridges
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2014-05-01
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[PDF-11.26 MB]
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Abstract:Current inspection procedures for suspension bridge main cables mainly consist of visually inspecting the exterior covering of the cable every 2 years. An indepth inspection is usually scheduled as necessary to assess the condition of the interior wires by wedging the cable at selected locations along the cable. However, such approaches were found to be deficient in uncovering the most deteriorated and weakest regions in the cables of several bridges during their full cable rehabilitation projects.
In this study, an integrated methodology was developed that uses state-of-the-art sensing capabilities and non-destructive evaluation (NDE) technologies to assess the cable condition. A smart sensor system integrated with NDE technologies is an approach that shows potential for assessing the condition of suspension bridge cables. NDE technologies for direct detection of the corrosion damage (i.e., main flux method, magnetostrictive technology, and acoustic emission technology) were implemented, validated, and tested for suspension bridge cable applications. In addition, a network of sensors that can monitor the external and internal environment of such cables and provide information that can be used to indirectly assess the cable's deterioration conditions and their evolution over time were assembled and extensively tested. In the selection of the sensors to be used for indirect sensing, special consideration was placed in considering the performance of such sensors in realistic service conditions such as a harsh environment, extreme reversals in cyclic histories (temperature, humidity, strain, electrochemical activity byproducts, etc.), large compaction forces, etc.
To recreate conditions as close as possible to real operating conditions, a cable mockup, which was 20 inches (508 mm) in diameter and 20 ft (6.1 m) long and subjected to 1,100 kips (4,893,043.76 N) and fully instrumented, was built at Columbia University and tested in an enclosed accelerated corrosion chamber. The results showed that the selected sensors were able to successfully measure temperature, humidity, and corrosion rate within the cable. The same system was then installed on two panels of the Manhattan Bridge, and measurements of temperature, relative humidity, and corrosion rate in the cable interior were successfully recorded for almost 1 year from November 2010 to September 2011.
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