Shigeki UEHARA
Development of the acoustic monitoring system for detection of PC cable breaking
Masatsugu NAGAI
The objective of this study is to develop a monitoring technique which can detect PC cable breaking in existing bridges. Herein, sound emitting from a PC cable when it breaks is paid to attentions. In particular, this study focused on the communication system which can connect to Internet on-site and the position identification of acoustic source.
At present, a developing acoustic monitoring system has been installed on an existing bridge, which is located in mountainous area. It is not easy to build an Internet connection environment on-site. Therefore, in this study, new communication system, which is a combination of a mobile router and remote control software, is incorporated into the existing system in order to connect Internet on-site. As a result, it was possible to read and process measured data at remote place. This can realize an immediate action when PC cable breaks.
There is one more problem on present investigation method for PC cable breakings because it is needed to drill a hole in a concrete slab to find defects. Therefore, this study aimed to develop a position identification method of acoustic source. At first, the method was formulated mathematically, and then simple laboratory experiment, which simulates PC cable breaking by hitting hammer, was carried out to validate the method. As a result, it was found that the position of acoustic source could be identified with an accuracy of about 0.30 m. The identification error is mainly resulted from the accuracy of reading time history. Frequency components other than acoustic source makes difficult to read data. Therefore, a band-pass filter was applied to measured data to improve the readability. Frequency range of the filter was determined based on the frequency characteristics of acoustic source. As a result, the accuracy of position identification was improved to about 0.13 m.
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