Measurement of the Cover Thickness of Reinforcing Bars in Concrete Structures by the Stress Wave Propagation
博士 === 國立中興大學 === 土木工程學系 === 87 === The objective of this thesis is to develop a new nondestructive technique for determining the cover thickness of reinforcing bars in concrete structures. Currently, the available equipment for detecting reinforcing bars is based on the electromagnetic methods. Whe...
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| Format: | Others |
| Language: | zh-TW |
| Published: |
1999
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| Online Access: | http://ndltd.ncl.edu.tw/handle/14330240955450991592 |
| Summary: | 博士 === 國立中興大學 === 土木工程學系 === 87 === The objective of this thesis is to develop a new nondestructive technique for determining the cover thickness of reinforcing bars in concrete structures. Currently, the available equipment for detecting reinforcing bars is based on the electromagnetic methods. When the spacing between reinforcing bars is small, the interaction of electromagnetic field between adjacent reinforcing bars results in detection failure due to difficult interpretation of signals. The new technique proposed in this thesis for detection of reinforcing bars makes use of stress waves instead of electromagnetic waves. The idea is derived from the fact that stress waves have a faster wave speed in steel bars than that in concrete. Because the propagation of stress waves follows the shortest travel path, the measured signal is mainly influenced by the reinforcing bar directly beneath the test point and has nothing to do with adjacent reinforcing bars. This is the reason why the stress wave technique can satisfy the need for detecting reinforcing bars in the areas containing congested bars. This thesis presents both numerical and experimental studies to investigate all the related parameters and their influences on measuring accuracy. The results obtained from these studies show that the distance between the impactor and the receiving transducer must be enough to make the P-wave incident on and refracted from a reinforcing bar with a critical angle and ensure its first arrival at the receiver. Consequently, the cover thickness of the reinforcing bar can be determined by knowing the transit time and the travel path of the P-wave through the reinforcing bar together with the measured P-wave speed of concrete.
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