Structural health monitoring of suspension bridge cables

This paper presents an update to the Corrosion Monitoring Research Study of New York City Suspension Bridges, which is funded by the Federal Highway Administration (FHWA). The objective of the research study is to develop, integrate and deploy a Corrosion Detection and Monitoring System (CDMS) for suspension bridge cables using direct and indirect sensing methods. The CDMS will be a combination of Nondestructive Evaluation (NDE) methods and technologies that will provide a continuous external and internal sensing system and will complement standard visual inspection for detecting changing conditions along a cable. The development of this technology can assist in improving the economy of inspection by identifying critical areas of the cable for prioritization of maintenance resources by reducing the need for costly in-depth inspections and/or rehabilitation. For a maintenance program requiring rehabilitation or repair, the system will provide continuous monitoring of the cable condition until the program is complete and then be used to determine the effectiveness of the maintenance program. This ongoing development is being performed by a team consisting of Columbia University, Parsons Transportation Group, and Physical Acoustics Corporation (PAC). The team is currently completing the building of a full-scale mock up cable in the Carleton Strength of Materials Laboratory at Columbia University, and will be 20 inches in diameter, 20 feet long and will be placed in a corrosion chamber. The mock-up is being used to evaluate the potential technologies, identified during the initial literature review, for detecting the onset of corrosion inside a suspension bridge cable and its development over time through direct and indirect methods. Direct methods are those that will detect and quantify corrosion damage inside the cables. Indirect methods will include sensors that can monitor external and internal environmental conditions; providing information that can be used to report on the likelihood of corrosion and its evolution over time. Current laboratory testing is using wire strands instrumented with different sensors that are subjected to extensive accelerated corrosion tests. Tests are conducted using different contaminant contents, levels of pH, temperatures and levels of humidity. The results are extensively evaluated in order to provide direct correlation between the measured quantities and level of deterioration with the actual condition of the strand. The information collected is being used to develop an algorithm for estimating the changes in cable strength. Once the most reliable and feasible monitoring techniques are established in the laboratory, and from the early field monitoring phase, a field demonstration will take place on one of New York City East River suspension bridges. The research will help demonstrate the applicability of structural health monitoring for other types of cable-supported bridges and infrastructure.