Membrane triangles with corner drilling freedoms. I: The EFF element (Q1205262)

This paper studies the formulation of 3-node, 9-dof membrane elements with normal-to-element-plane rotations (the so-called drilling freedoms) within the context of parametrized variational principles. These principles supply a unified basis for several advanced element- construction techniques; in particular, the free formulation (FF), the extended free formulation (EFF) and the assumed natural deviatoric strain (ANDES) formulation. In Part I we construct an element of this type using the EFF. This derivation illustrates the basic steps in the application of that formulation to the constructing of high-performance, rank- sufficient, nonconforming elements with corner rotations.