Devriendt C., Guillaume P.

Experimental modal analysis allows us to identify the dynamic behaviour of a structure from the knowledge of the applied forces and the measured responses, using the frequency response functions. In the case of structures in operational conditions we often do not know these forces. For instance, civil structures (e.g. bridges, buildings, off-shore platforms, etc.) and machinery, in operating conditions, who are excited by unmeasurable ambient excitation sources (e.g. traffic, wind, waves, etc.) For these situations output-only techniques were developed using the responses only. These techniques have serious limitations because they can only be applied under the assumption that the forces are the result of a stochastic process, so being white noise. This is no longer necessary for the proposed transmissibility-based approach. The unknown operational forces can be arbitrary (colored noise, swept sine, impact ...) as long as they are persistently exciting in the frequency band of interest. In general, the poles that are identified from transmissibility measurements do not correspond with the system’s poles. However, by combining transmissibility measurements under different loading conditions, it is shown in this paper that model parameters can be identified. An experimental test validates the proposed technique.