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Structural Engineering and Mechanics
  Volume 69, Number 6, March25 2019 , pages 615-626

Function space formulation of the 3-noded distorted Timoshenko metric beam element
S. Manju and Somenath Mukherjee

    The 3-noded metric Timoshenko beam element with an offset of the internal node from the element centre is used here to demonstrate the best-fit paradigm using function space formulation under locking and mesh distortion. The best-fit paradigm follows from the projection theorem describing finite element analysis which shows that the stresses computed by the displacement finite element procedure are the best approximation of the true stresses at an element level as well as global level. In this paper, closed form best-fit solutions are arrived for the 3-noded Timoshenko beam element through function space formulation by combining field consistency requirements and distortion effects for the element modelled in metric Cartesian coordinates. It is demonstrated through projection theorems how lock-free best-fit solutions are arrived even under mesh distortion by using a consistent definition for the shear strain field. It is shown how the field consistency enforced finite element solution differ from the best-fit solution by an extraneous response resulting from an additional spurious force vector. However, it can be observed that when the extraneous forces vanish fortuitously, the field consistent solution coincides with the best-fit strain solution.
Key Words
    metric element; function spaces; symmetric formulation; element distortion; best-fit paradigm; variational correctness; orthogonal projections
S. Manju: CSIR-National Aerospace Laboratories, Bangalore 560017, India
Somenath Mukherjee: CSIR-Central Mechanical Engineering Research Institute, Durgapur 713209, India

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