Explanation of Support Nonlinearities on Example | 1.2 Translation

Technical Article

RFEM and RSTAB provide numerous options for nonlinear definitions of nodal supports. Continuing my previous article, this article further describes options for creating a nonlinear free support and provides a simple example. For better understanding, the result is always compared to a linearly defined support.

General

Each nodal support has its own local axis system. The axes are designated as X', Y' and Z'. By default, this support axis system is based on the global axis system of the RFEM or RSTAB file. However, it is also possible to define a custom axis system or a rotation. In the example provided here, the support axis systems are shown for all nodal supports. The options of the individual nonlinearities are shown for the displacement in X'. For the other two support axis directions, the similar definitions apply.

Note: The nonlinearity always refers to the acting support force.

Diagram: Tearing

Figure 01 - Diagram: Tearing

In the diagram, the load-deformation behaviour of a support can be reproduced very close to reality. In the case of 'yielding', the support fails after reaching the greatest positive or the smallest negative support force. The positive and negative zones can also be defined independently of each other. In Figure 01, the acting load was selected in such a way so as to represent the state shortly before reaching the tearing.

Diagram: Yielding

Figure 02 - Diagram: Yielding

If the defined deformation is reached, the support force does not rise anymore in further load increments. This state is referred to as 'yielding'. The deformation can further increase, but the support force does not exceed the maximum value defined. It is also possible to specify this differently for the positive and the negative zone.

Diagram: Continuous

Figure 03 - Diagram: Continuous

After reaching the maximum deformation defined, the support force and the deformation continue to increase linearly. The ratio is defined by the gradient of the straight line, described by the last two diagram entries.

Diagram: Stop

Figure 04 - Diagram: Stop

As with the deformation greater than the last value in the diagram, the support's effect is full. The node is then preserved completely for the defined direction.

Friction PY'

Figure 05 - Friction PY'

In this case, the support definition takes into account the support force acting in the direction Y'. By defining the friction coefficient, the maximum value of the support force in X' relating to the support force in Y' is set.

Friction PZ'

Figure 06 - Friction PZ'

The support definition takes into account the support force acting in the direction Z'. By defining the friction coefficient, the maximum value of the support force in X' relating to the support force in Z' is set.

Friction PY'PZ'

Figure 07 - Friction PY'PZ'

This option allows you to model the support by using the vector of PY' and PZ' as well as the friction coefficient.

Friction PY'+PZ'

Figure 08 - Friction PY'+PZ'

If the support is designed in such a way that there is a different friction coefficient for Y' and Z', you can use this support definition. The respective support force is multiplied by the specified friction coefficient, and both components are then added together to form the governing support in X'.

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RFEM Main Program
RFEM 5.xx

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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

RSTAB Main Program
RSTAB 8.xx

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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions