Operational influence of the nature of the damping considered in the adjustment of the structural response model on the results of the scale factors for operational modal analysis

The consideration of the assumption of viscous damping as a starting hypothesis in the dynamic analysis of structures can introduce a substantial error in the calculations. This is due to the energy dissipated by the structure in its oscillation being frequency dependent under that premise, while experimentally the opposite becomes apparent, when structural or hysteretic damping is taken into account. The modes of vibration obtained in the operational modal analysis are not scaled, since the magnitude of the excitation on the structure is unknown. For this reason it is necessary to resort to additional calculation procedures, such as the mass change method, to determine the scale factors of each mode. However, all variants of this method, in the current state of the art, have been deduced in the undamped situation. In this paper we analyze the influence of the deviation of the results for the scale factors, obtained by means of a viscous damping analysis, compared to that same deviation determined under the consideration of hysteretic or structural damping, independent of the frequency, whose results align much better with the experimental behavior of the structure