Operational modal analysis of a plan-asymmetric RC frame structure subjected to a simulated random ground motion along different directions

The present work aims at performing an output-only modal identification starting from the dynamic responses of a plan-asymmetric RC frame structure that is subjected to a random ground motion along different directions. The main purpose is to evaluate the accuracy of the identified modal model for each direction of the exciting input, which is an unmeasured white noise signal. The Eigensystem Realization Algorithm is the applied identification method and it could be extended to the Operational Modal Analysis by adopting adequate pre-identification procedures. Two of them, which are the Natural Excitation technique and the Random decrement method, are separately applied and compared. All the identification procedures are performed on simulated data and the results show that the identification of the mode shapes of the structure is influenced by the direction of the applied ground motion; however, the main modes of the structure are always identified while some uncertainties occur for the modes at the highest frequencies, especially for the torsional ones. Notwithstanding the classical assumption of the OMA are not completely satisfied by the considered input, the obtained results, compared with the known analytical structural model, demonstrate the effectiveness of the algorithm.