Periodic structures can be often seen in the industrial reality. Numerous studies focus on this problem. To explain the basic behaviour, different kinds of subsystem has been considered. One degree of freedom system like a pendulum [1) or like aspring-mass system [2], multi degrees of freedom like axially vibrating roads [3], simply supported beams [4] or plates in the same plane coupled by longitudinal stiffeners [5].Here, periodic lattices of plates connected with an angle different from zero are studied. The purpose is to identify the usual behaviour of lattice (which pass-bands and stop-bands) but also to explain the rise of the amber-band.In a previous work [6] the analytical formulation for coupled plates describing the in-plane and flexural motions has been given. By sake of simplicity we recommend the reader to find the mathematical development in ref [6].We can propose a brief summaryof the analytical way used to solve the vibrational formulation is based on three points:(1) The motion of a plate is expressed with the Donnell operator for a shell of infinite radius, (2) It is developed with a semi-modal decomposition combined to a wave formulation and (3) the expression of the continuity of motions and forces at theconnection between two plates gives rise to a matricial equation whose the unknowns are the coefficients of the semi-modal decomposition.And example of the structure under study is proposed figure 1: eighteen equivalent steel plates 0.4×0.5×0.002 m, connection angle: 90°.
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