Mathematical homogenization (or averaging) of composite materials, such as fibre laminates, often leads to non-isotropic homogenized (averaged) materials. Especially the upcoming importance of these materials increases the need for accurate mechanical models of non-isotropic shell-like structures. We present a second-order (or: Reissner-type) theory for the elastic deformation of a plate with constant thickness for a homogeneous monotropic material. It is equivalent to Kirchhoff's plate theory as a first-order theory for the special case of isotropy and, furthermore, shear-deformable and equivalent to R. Kienzler's theory as a second-order theory for isotropy, which implies further equivalences to established shear-deformable theories, especially the Reissner-Mindlin theory and Zhilin's plate theory. Details of the derivation of the theory will be published in a forthcoming paper [3]. For an arbitrary three-dimensional body Ω ⊂ R 3 , which is assumed to be a bounded region, with the boundary regularity ∂Ω ∈ C 0,1 (this assumption allows to treat basically every body in engineering applications) and a boundary decomposition of the type ∂Ω = ∂Ω 0 ∪ ∂Ω N and ∂Ω 0 ∩ ∂Ω N = ∅, with ∂Ω 0 = ∅ relatively open and ∂Ω N relatively open, one can proof that the three-dimensional weak formulation of the mixed-boundary-value problem of linear elasticity (II) has a unique solution under very weak assumptions for the regularity of the given data, i.e., the prescribed displacement field u 0 on ∂Ω 0 , the prescribed traction-vector field g on ∂Ω N and the prescribed field of body force f . If we assume that the component functions of the fourth-order elasticity tensor E ijrs : Ω −→ R are continuous or piecewise constant and fulfill the symmetry relations E ijrs = E jirs , E ijrs = E ijsr and E ijrs = E rsij , so that in addition the associated 6 × 6-elasticity tensor is symmetric positive definite for all x ∈ Ω (which is a basic modeling assumption in continuum solid mechanics), we get:Theorem: Existence and uniqueness of the weak solution of the three-dimensional linear elasticity problemThen there exists an u 0 ∈ X that fulfills the weak displacement-boundary condition S u 0 (x) = u 0 (x) for almost all x ∈ ∂Ω 0 (with respect to the corresponding Lebesgue measure) and the problemsare equivalent and have a unique solution.Here S : W 1,2 (Ω) −→ W 1/2,2 (∂Ω) denotes the trace operator, X := W 1,2 (Ω) 3 and X 0 := {v ∈ X|∀i ∈ {1, 2, 3} :Sv i = 0 on ∂Ω 0 }. Problem (I) corresponds to the "principal of minimal potential energy" in a weak setting, which is usually the starting point of the derivation of consistent theories (e.g. in [1]). We use problem (II) as a starting point instead.We now assume our body to be a plate of constant thickness h. Therefore, let the mid-plane A ⊂ R 2 be a bounded region with ∂A ∈ C 0,1 and Ω :. For the boundary decomposition we assumeFurthermore, we introduce the plate parameter c :=, where a is a characteristic in-plane length of the plate, e.g., the diameter of A. The plate parameter is a dimensionles...