Another FEM: Rectangular element of 4 nodes

Abstract

In both of the traditional FEM and the proposed methodology in this article, the compatibility equations are obtained from the same interpolation functions, so the elementary matrix that relates deformations in the nodes of the element with the displacements of that nodes are the same in both procedures. But, whereas in that one the PVW is applied to establish the Equivalent Nodal Forces to be used for the achievement of the equilibrium equations of all the nodes of the structure, in which these forces are obtained from the hypothesis that the stresses on all four sides of the elemental rectangle vary linearly along these sides and are thus to replace said stresses as statically equivalent, concentrated forces. Since the system of equations used in this procedure is given in all the unknowns of the problem explicitly, and it is possible to impose any kind of restriction on any of these unknowns, so that, in addition to the conditions of essential support to avoid movement as a solid rigid, conditions of equilibrium are imposed on every one of the elements that discretize the structure, as well as the conditions of tension in the perimeter of the domain; conditions that, since it is not possible to be considered with the traditional FEM, this one is forced to sink some errors originated by a greater distance between the modeling to be adopted and the physical real fact. The practical examples studied, using as a base the rectangular element of 4 nodes, show somewhat improved results with respect to those obtained with the traditional FEM.

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