**5. Conclusions**

In order to validate the feasibility of a frequency-based damage detection method, which is a well-known concept but has seen minimal practical application within the realm of railway concrete sleepers, this study experimentally investigated the impacts of artificial or actual damage on the modal characteristics of such sleeper. In addition, an efficient detection method based on sound pressure and its applicability for practical use was empirically validated. The associated resulting conclusions are summarized as follows:


When comparing the natural frequencies of the third mode obtained by the noncontact measurement techniques presented in this study, many deep damaged concrete sleepers can ultimately be detected from a large number of those measured. Furthermore, the proposed process can significantly contribute in the determination of sleeper-exchanging priorities according to the amount of measured frequency reduction in various cases.
