Mixed finite element formulations and related limitation principles: a general treatment Original Research Article

The complete set of variational principles for an elastic structural model with non-homogeneous boundary conditions and inelastic strains is presented. A general methodology for deriving the approximate mixed formulation and the relevant matrix form is also shown and applied. The limitation principles for a structural model with a linear elastic behaviour are derived and it is shown that each principle relating two different approximate formulations depends upon the state variable interpolated in one formulation and not in the other.