Experimental investigation of vibration localization in disordered multi-span beams

The results of an experimental investigation of the effects of span length disorder on the dynamics of a mono-coupled, multi-span beam are reported. Two experimental specimen are considered: a nominally periodic twelve-span beam with equal spacing between simple supports, and the corresponding disordered beam which features slightly randomly spaced supports. Experimental results demonstrate that the transmission of vibration which takes place within the frequency passbands of the periodic beam is greatly hindered when span length randomness is introduced. The spatial localization of both the mode shapes and the steady-state harmonic response to an end excitation is observed in the disordered twelve-span beam, especially for frequencies which lie within the second passband. Very good quantitative agreement is obtained between experimental results and theoretical findings for both ordered and disordered configurations. Furthermore, an experimental estimation of the localization factor yields satisfactory agreement with the theoretical result for an infinite multi-span beam. This work reports one of the first systematic experiments carried out to demonstrate the occurrence of vibration localization in nearly periodic structures.