Self-Monitoring Surveillance System for Prestressing Tendons: Phase I Small Business Innovation Research (NUREG/CR-6420)
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Manuscript Completed: November 1995
Date Published: December 1995
Construction Technology Laboratories, Inc.
5420 Old Orchard Road
Skokie, IL 60077
H. L. Graves, NRC Project Manager
NRC Job Code W6475
Division of Engineering Technology
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001
Assured safety and operational reliability of post-tensioned concrete components of nuclear power plants are of great significance to the public, electric utilities, and regulatory agencies. Prestressing tendons provide principal reinforcement for containment and other structures. In this phase of the research effort, the feasibility of developing a passive surveillance system for identification of ruptures in tendon wires was evaluated and verified. The concept offers high potential for greatly increasing effectiveness of presently-utilized periodic tendon condition surveillance programs.
A one-tenth scale ring model of the Palo Verde nuclear containment structure was built inside the Structural Laboratory. Dynamic scaling (similitude) relationships were used to relate measured sensor responses recorded during controlled wire breakages to the expected prototype containment tendon response. Strong and recognizable signatures were detected by the accelerometers used. It was concluded that the unbonded prestressing tendons provide an excellent path for transmission of stress waves resulting from wire breaks.
Accelerometers placed directly on the bearing plates at the ends of tendons recorded high-intensity waveforms. Accelerometers placed elsewhere on concrete surfaces of the containment model revealed substantial attenuation and reduced intensities of captured waveforms. Locations of wire breaks could be determined accurately through measurement of differences in arrival times of the signal at the sensors. Pattern recognition systems to be utilized in conjunction with the proposed concept will provide a basis for an integrated and automated tool for identification of wire breaks.