Modal Analysis of a Frame Model Under Unmeasured Seismic Input

The paper reports the first results of an experimental campaign aimed at the validation of a procedure, proposed in previous theoretical works by one of the writers, for the structural identification in frequency domain of linear structural systems subjected to base seismic excitation. Differently from the classical identification techniques based on the transfer-function processing, that require to measure the excitation (input-output problem), such procedure allows the solution of the identification problem also in case of unknown input (output-only problem) if the responses of at least three degrees-of-freedom are available for the system. An experimental campaign has been carried out on a three storeys shear-type frame, carefully designed in order to minimize the uncertainties and errors. After validating the model setup and the measuring chain by means of a classical input-output procedure, the paper discusses the first results of the output-only identification. The outcomes show a fair agreement with the results obtained by including the input knowledge.