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Figure 01 - Finite Elements

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FAQ 002960 EN 17 April 2019

Markus Baumgärtel Calculation RFEM RSTAB

Which shape function is used in RFEM?

Answer

The finite element types used in RFEM are given in the following table. They are chosen automatically

by the program according to the situation.

Element Type Element description

1D: beam element element with rotational degrees of freedom

2D: plate element Lynn–Dhillon; MITC3; MITC4 – used in case of nonlinear calculation

2D: wall element with stabilized zero energy modes

2D: shell element shell element = plate element + wall element

3D: solid element element with rotational degrees of freedom; element without rotational degrees of freedom (with or without extra shape functions)

gas element

contact element

Integration Procedure

For members, analytical integration is used for linear cases, while in the nonlinear setting the two

point Gauss quadrature is used along the beam. For nonlinear cases the following integration rule

is used in the cross-section: 2×2 Gauss quadrature for quadrangles and 4-point selective reduced

integration rule for triangles (3 points for 𝜖x, 𝜖y and 1 point for 𝛾xy).

In plate elements, analytical integration is used whenever possible (in Lynn–Dhillon element or in

a triangular element). In other cases, a 2×2 composite Gauss quadrature is used in the element

plane (quadrangles). In solids, a 2×2×2 composite Gauss quadrature is used in hexahedrons.

Reduced one point integration is used for some particular terms to avoid numerical problems.

Let us focus on integration in plates with respect to their thickness, which is based on the Gauss–Lobatto quadrature. The Gauss–Lobatto quadrature is a Gauss quadrature in which boundary points

are forced to also be integration points, which allows an exact evaluation of stresses on layer

interfaces in case of multilayered plates. In case of linear calculation, three integration points are

used per layer. In nonlinear calculation, nine integration points are used in the plate (nonlinear

calculation allows one layer only).

Keywords

Shape function Finite Element

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