At present, the establishment of the non-destructive inspection technique in the structure maintenance becomes a matter of worldwide interest. Especially, the soundness evaluation of masonry structures that have been serving for a long period is indispensable. Basic research for applying acoustic emission technique (AET) to masonry structure was carried out. In the study of frequency component and attenuating of the elastic wave propagating through brick test-piece, it was confirmed that the principal frequency band of elastic wave was not exceeding 100kHz and the elastic wave was scarcely attenuated by the joints of brickwork in the lower frequency band than 100kHz. In the second study to examine the possibility of the practical application of AET, AE from the brick test-pieces were observed while the loading tests. The results of AE source location clearly showed that the damaging process was recognised by distribution of the AE sources. In the last study of practical masonry bridge monitoring using 8-channels AE analyser, the measurements were carried out separately for some parts of the bridge under the usual traffic. Because it was a traffic situation made quiet, the generation behaviour of AE was small. However, when a heavy-duty truck passed, AE generation was observed.
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