Dynamic damage identification based on measurements on a railway bridge with a laser-Doppler-vibrometer

Through rapid development of new measurement techniques nowadays a wide range of measurement procedures is available to reveal the condition of a construction. In a modern approach the dynamic response of a considered structure is recorded followed by data analysis to determine its dynamic structural parameters. In this diploma thesis the method of modal damage detection/identification and the energy cascading phenomena, which are both based on this basic concept, are applied. The first part of this thesis deals with the functionality of a Laser--Doppler--vibrometer, which is the utilized measurement system, its hardware components and the provided software. This measurement device allows contactless analysis of parts of the structure from distance and forms the basis of all performed measurements. Subsequently the theory of damage identification (or rather damage detection) from studying the recorded vibration data is treated. This includes the identification of damage due to the analysis of modal parameters. Furthermore, a method for damage detection based on an energy observation (energy cascading phenomena) is briefly described and discussed. In the second part the two test specimens as well as the performed measurements are described. After specifying the structure, the choice of the considered connection detail of the railway bridge is discussed. Based on the gathered knowledge a second test object -- a generic specimen in form of a steel plate -- is selected and analysed. The third part deals with the analysis of the measurement records of the railway bridge and the test specimen with respect to the described theories. It is investigated, whether the described effects of damage can be detected through the analysis of the recorded measurement data. In particular, the relevance of the theory of the energy cascading phenomena is verified. Finally the compiled knowledge is summarised and an outlook to further damage detection methods is provided.



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