Suspension Bridge Cable Inspection System

The MsS system for inspecting suspender bridge cable was developed at Southwest Research Institute^® under funding by the Federal Highway Administration (FHWA), the Department of Transportation, USA, and commercialized in 2005. The MsS system has been used by inspection service companies.

This example shows field evaluation of guided wave inspection of suspender ropes on a bridge in New York City. From a test location above the sidewalk of the bridge as shown in the figure, a pulse of 10-kHz longitudinal guided waves was launched along the length of the suspender and the reflected signals from geometric features and defects in the suspender were detected without requiring any paint removal.

The sample figure is plotted to compare data from new and used suspender cables. Symbols used to describe and indicate the signals in the data are as follows: SK - socket, Si - separators, Gi - gatherers, Di - defect indications, where i = 1, 2, 3, etc. Four suspender cables tested with MsS sytem are shown. The first trace is data taken from newly replaced suspender and the data in the 2nd through 4th traces were taken from three existing suspenders. It was found that the 2nd one was in the worst condition, followed by the 3rd one, and, then, the 4th one that was in almost as good a condition as the new suspender. The test results showed that, from a single test location and without scanning the sensor along the rope, the MsS system could examine the entire length of the suspender rope (from the socket to the main cable including the region over the main cable band) that was more than 100-meters (330-feet) long.

The data given in this figure clearly demonstrate the capability of the MsS technique for inspecting the entire length of suspender ropes from the sidewalk of the suspension bridge. Using guided wave for inspecting suspender cables is cost- and performance-effective method and is suitable for structural condition assessment.