The National Academies

NCHRP IDEA 20-30/IDEA 152 [Completed (IDEA)]

Bridge Cable Inspection with Long-Range Ultrasound
[ NCHRP 20-30 (NCHRP-IDEA) ]

  Project Data
Staff Responsibility: Dr. Inam Jawed
Fiscal Year: 2010

This project developed and demonstrated the application of a rapid and reliable non-destructive method based on long-range ultrasound for inspecting bridge cables. The project was initiated by developing  a basic inspection specification for bridge suspender ropes and cables less than 3 inches in diameter.  Using this specification, an initial laboratory testing plan was documented for single legged and double legged suspender rope which included length of rope, defect type, and location. Field testing of the technology was performed on the Manhattan Bridge suspender ropes. Of the five ropes tested, all of them contained cross-sectional area changes that were identified using guided wave ultrasound.  On three of the ropes, it was possible to visually confirm the presence and location of each cross-sectional area change detected.  On two of the ropes, it was impossible to visually confirm the presence of the cross-sectional area reduction due to access problems.  The Manhattan Bridge suspender ropes were taken out of service and inspected visually to confirm the presence of cable defects.    Also, during this reporting period, the feasibility of inspecting the main cable of a cable stay bridge was studied for the first time.  From one sensor position, the technology scanned approximately 120 feet from a single sensor position.  Ultrasonic data were acquired at 4 four different locations.  A total of 4 Collar reflections were observed at every 20 feet.  Between the collars, no significant reductions in cross-sectional area due to wire breaks or corrosion were observed.  The study showed, for the first time, that main cables may also be inspected with the proposed technology. Laboratory testing focused on obtaining out-of-service suspender ropes for controlled testing in-house and at Lehigh University.  The first socketed rope was tested in-house.  Wire breaks were then inserted at the cable socket interface. Data were acquired at 5, 10, 15, 25 and 50% cross-sectional area (CSA) reduction.  The results demonstrated clearly that the proposed technology is sensitive to changes in CSA as small as 5%.  More importantly, the results showed that changes in some waveform features correlated to the increase in damage size.    Full scale testing on a tensioned cable was also performed at Lehigh University.  Wire breaks were inserted at the cable-socket interface from 3 to 25% CSA.  These results also showed that the technology was sensitive to changes as small as 3% CSA and that there is a strong correlation between changes in select waveform features and increases in CSA loss. Similar tests were performed on a double legged suspender rope at Lehigh University.  The objective of the test was to determine if the technology could detect wire breaks at the gatherer.  After baseline data was acquired, wires cuts were inserted until about 25% cross-sectional area reduction occurred.  The tests confirmed that wire breaks was sensitive to wire breaks at the gatherer.  Wire breaks equivalent to 3 % CSA were detected. Finally, a commercialization plan for the technology was documented.  An initial estimate to retrofit a bridge with the technology was completed.  The cost to inspect one bridge using the retrofitted technology was also estimated.  Initial estimates put the retrofit and periodic inspection costs at $34,000 and $8,000, respectively, for a 200 cable bridge.  The contractor's final report is available.

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