Suspension Cable Wire Break Monitoring Using Acoustic Emission for Economic and Probability of Detection Advantages

After several decades of service, main suspension cables on bridges require internal inspection and evaluation. Unwrapping a minimum of three panels per cable along the full length between cable bands and wedging between the strands to allow inspection throughout the cross section is required. The cable panels should then be rewrapped with specialized equipment. Additional areas may be added if findings warrant. In order to better assess the current cable condition and develop a future inspection and maintenance program, an internal inspection and evaluation of other areas along the cable is required. This inspection should be performed in accordance with the recommendations of NCHRP Report 534 “Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables,” a nationally recognized and recommended guide for such inspections. NCHRP 534 also recommends acoustic monitoring as the best currently available technology for monitoring suspension bridge cables, obtaining an inventory of wire failures, maintaining accurate data on the location of failures, and estimating the rate of cable degradation. This paper will discuss the economic advantages of implementing a wire-break monitoring system. It will also discuss using acoustic emission monitoring to increase the probability of wire-break detection (POD) to >90% and perhaps 100%, as opposed to a POD of <3% with just opening and wedging.

References
1. Camo, P.E., Sante. – Reliability of Damaged Parallel Wire Cables, Weidlinger Associates, Inc. New York, NY 10014. 2. NCHRP Report 534 Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel Wire Cables. 3. Nickerson, R. NCHRP Web Document 20 Project 20-07/Task 100, Safety Appraisal of Suspension Bridge Main Cables. Contractor’s Report from a Workshop in Newark, New Jersey November 16-17, 1998. NBE, Ltd., Hampstead, MD.
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