Calculating the energy-norm FEM-error for Reissner-Mindlin plates without known reference solution

The validation of (recently introduced conforming) finite element technolog ies for the numerical treatment of Reissner-Mindlin plate models requires c omparisons with the unknown exact solution. Since mathematical results are often provided for the error in energy norms only it is not sufficient to c ompare a typical displacement or moment at one point of the domain. Instead of computing a reference solution on a very fine mesh (and then providing a lot of data for the public) we propose the storage of one (problem depend ing) constant C which then allows an error representation which merely invo lves known quantities. Based on this approach we could verify convergence r ates which were theoretically predicted and give experimental evidence that new adaptive automatic mesh-refining algorithms yield superior approximati ons. Given any reasonable guess of C (computable from known quantities), ou r error representation yields an approximation for the unknown error. This establishes a method for a posteriori error control to be employed as a ter mination criterion.