Explanation of Support Nonlinearities on Example | 1.2 Translation

Technical Article

RFEM and RSTAB provide numerous variants of the nonlinear definitions of nodal supports. In the following, in continuation of an earlier article , the other possibilities of nonlinear support design for a displaceable support will be shown by 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 defined as X', Y' and Z'. By default, this axis system is based on the global axis system of the RFEM/RSTAB file. However, it is possible to define a custom axis system or simply a rotation. In the example shown here, the support axis systems are displayed for all nodal supports. The possibilities 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

In the diagram, the load-deformation behavior of a support can be represented very realistically. In the case of the definition "Tearing", the support fails after reaching the greatest positive or the smallest negative support force. The areas for the positive and negative diagram area can also be defined independently of each other. In Figure 01, the acting load has been selected in such a way that the state is displayed shortly before the breaking point is reached.

Diagram: Yielding

If the defined deformation is reached, the support force does not rise anymore in further load increments. This state is called "flow". 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

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

Diagram: Stop

As of 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 '

In this case, the support is defined by considering an acting support force in direction Y '. By defining a friction coefficient, the maximum value of the support force in X 'is related to the support force in Y'.

Friction PZ '

The support is defined by considering an acting support force in direction Z '. By defining a friction coefficient, the maximum value of the support force in X 'is related to the support force in Z'.

Friction PY'PZ '

With this option, the support is created by using the vector of PY 'and PZ' as well as a common coefficient of friction.

Friction PY '+ PZ'

If the support is designed in such a way that there are different friction coefficients for Y 'and Z', this can be realized with this support definition. The respective support force is multiplied by the specified friction coefficient and then the two components for the governing support in X 'are added up.