204 減衰特性を利用した瓦の亀裂の検出  [in Japanese] A Study on Crack Detection of Roof Tile Using Damping Factor  [in Japanese]

This paper describes a study on crack detection of roof tiles by using damping factor of the vibration response with impact test. Damping ratio of roof tiles are calculated from logarithmic amplitude of the envelope of response for each natural frequency. The envelope of response is obtained from the analytic signal that has a real part which is the vibration response and an imaginary part which contains the Hilbert transform. Damping ratio for several natural frequencies of a roof tile become large greatly by a crack. Others are almost changeless. The relations between the variation of damping ratio by a crack and the vibration mode shapes are investigated by using experimental modal analysis. The result shows that a crack on a roof tile can be detected by the variation of damping ratios.