Simple and mixed shear deformable theories accounting for the transverse sh
ear, in the sense of Reissner-Mindlin's thick plate theory, are employed in
the construction of variational statements for rectangular flat plates. An
alytical solutions for natural frequencies and buckling loads of anisotropi
c plates under various boundary conditions are developed. A variety of simp
ly-supported, clamped and free boundary conditions is considered, and compa
risons with the existing literature are made.