Vibrational characteristics of non-proportionally damped structures can quite accurately be predicted by complex mode superposition. However, solving a complex eigenvalue problem and using complex modes increase the computational effort considerably. Approximate methods, therefore, are preferred in several applications. Almost in all approximate modal analysis methods, real modal vectors are employed by making proportional damping approximation. In this work dynamic behavior of damped beams, harmonically excited at frequencies around a resonance frequency is investigated by using the results of a set of experiments conducted with proportionally and non-proportionally damped aluminum beams. The main attention is focused on the contribution of the in-phase component of the receptance (or inertance) to the total response at undamped natural frequencies as well as at resonance frequencies. The change of this contribution by the point of excitation and/or point of measurement is also investigated. Thus, the cases and conditions for which some approximate methods for the dynamic analysis of non-proportionally damped structures have acceptable accuracy are experimentally studied. A better understanding of the dynamic behavior of damped structures when excited around resonance frequencies is also obtained.
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