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Main Cable Corrosion Monitoring for Suspension Bridges Using a Nondestructive Sensing System

The corrosion of the high-strength steel wires of a suspension bridge’s main cable has been attributed to the environment within the cable wrapping. A sensor network was developed to monitor the environmental conditions and corrosion rates within a main cable. Both the sensors and the system functionality were tested on a full-scale mock-up cable. An environmental chamber was built around the cable mock-up so as to subject the test specimen and sensor network to an aggressive corrosive environment created by cyclic temperature and humidity conditions. Temperature, relative humidity and corrosion rate levels were recorded by all sensors. The recorded data was analyzed in an attempt to determine general trends and correlations between the environmental variables themselves and their effects on corrosion rates. Recorded temperature fluctuations were highly dependent upon sensor depth within the cable; relative humidity levels, however, were not. During cyclic testing, near linear temperature increases and relative humidity decreases were recorded close to the cable’s center. Baseline corrosion rate levels were affected by relative humidity levels, with significant increases in corrosion rates at relative humidity levels greater than 50%. Temperature changes proved to impact corrosion rates on a cyclic level, with high correlations between the temperature and corrosion rate readings recorded by the LPR corrosion rate sensors. The proposed sensing system has been installed in one of the main cables of the Manhattan Bridge. The in-service monitoring system has had great success in providing up-to-date information to establish a robust image of the environmental conditions within the cable cross section. The in-service environmental trends correspond well with those observed in laboratory testing.

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