The response of two-dimensional periodic structures to harmonic point loading: A theoretical and experimental study of a beam grillage

This work is concerned with the response of a beam grillage system to a harmonic point load. This system serves as a particular example of a two-dimensional periodic structure, and the aim of the work is to validate a number of recent results regarding the general nature of the response of such structures to a localized excitation source. The grillage is analyzed by using the hierarchical finite element method to model a single period and then employing periodic structure theory to yield the ''phase constant surfaces'' which are needed for the forced response analysis. The theoretical work is complemented by an experimental study of a grillage system; a relatively high level of damping treatment is employed to produce a non-reverberant system that behaves in a similar manner to an infinitely extended system. Both the theoretical and experimental results show that the response can exhibit highly directional ''beaming'', the spatial pattern of which is strongly dependent on the excitation frequency, and this finding is fully consistent with the findings of the aforementioned general study. (C) 1997 Academic Press Limited.