In this paper the asymptotic behaviour, with respect to the small peri
od, of equilibrium displacements corresponding to the Koiter's shell m
odel of periodically perturbed plate is studied. The new model for tra
nsverse deformation of a wrinkled plate is obtained in the two-scale f
orm and the convergence result, as period tends to zero, is slated. In
the case of wavy plate the effective coefficients are explicity compu
ted.