Case Study: Tracking the Performance of Suspender Ropes at the George Washington Bridge using Nondestructive Testing Technique

Select suspender ropes were inspected at the George Washington Bridge (GWB) in New York City using a nondestructive testing (NDT) technique. This NDT technique involves the use of a long-range guided wave technology called “magnetostrictive sensor (MsS)”. The MsS technology is especially useful in areas that are difficult to access, such as the socket end of the ropes located below the sidewalk and the section of rope over the main cable band, and was found to be an effective tool for detecting degradation of suspender ropes at the GWB. The majority of the GWB suspender ropes have been in service for over 75 years. The MsS NDT was performed twice, in the years 2001 and 2005, to ascertain the condition of the ropes at the time of testing and estimate the future condition of the ropes. This paper presents a cross-classification model that enables estimates of rope condition data such as number of degraded wires and ultimate load static strength to be obtained from nondestructive MsS test results. Historically, the number of degraded wires and the ultimate load static strength were obtained from visual inspections and destructive physical tests, respectively at the GWB. Also discussed is a procedure to predict future condition of the GWB suspender ropes. Engineers and managers of suspension bridges similar to the GWB will find the discussions and results presented in this paper useful.

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