Mixed finite elements, using unsymmetric stresses, for linear analysis of plates

A mixed model for a Reissner-Mindlin-type plate is presented, where local stresses (rather than stress resultants and moments) are explicitly modeled. By following the ideas already used for membranes (see [23]), it is assumed that in plane shear stresses are not a priori symmetric. This choice allows the decoupling of the equilibrium equations, and involves introducing an in plane infinitesimal rotation field, corresponding to drilling dofs. Out-of plane shear stresses are then chosen such that equilibrium equations are exactly satisfied. Details of the formulation are provided, and the performances of the new element are assessed with reference to well-established benchmark problems