A study on the diagnosis system using the rotary hammering sound based on the structural vibration and acoustic theory

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Recently, it becomes very important to maintain the existing(aging) reinforced concrete structures in Japan. In order to minimize their life-cycle cost, many researches on the nondestructive evaluation technique have been conducted. However, most of nondestructive tests have problems related to their expense or measurement condition. Thus, visual inspection and conventional hammering sound test are usually applied as an effective method. But, the hammering sound test requires a high degree of skill to evaluate hammering sound and theoretical investigation has not well conducted on the acoustic mechanism of the hammering sound test. Therefore, this study appraises the capabilities of conventional hammering test and the rotary hammering test by means of the experiment using mortar specimens and existing bridges. Furthermore, acoustic analysis based on finite element method is conducted in order to grasp influences of defect on the hammering sound. The following results are obtained in this study.1)It is recognized that maximum sound pressure increase due to the existence of inner defect.Whereas,damping performance decrease due to the effect of defect.2)We confirmed the results of rotary hammering sound test shows clear adn significant influence of inner defect on their impact sounds. Therefore as for the diagnostic capability, the rotary hammering test is superior to conventional hammering test.3)Identification of defect condition by sound pressure information was attempted using the Self-Organizing Map algorithm and it is confirmed that the size of defect was clearly identified using the result of SOM.4)In addition,combination use of sound pressure and frequency information by time-frepuency analysis could evaluate precise defect conditions.