Explanation of Support Nonlinearities on Example | 1.2 Translation
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.
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.
In the diagram, the load-deformation behavior 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.
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.
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.
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.
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.
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.
This option allows you to model the support by using the vector of PY' and PZ' as well as the friction coefficient.
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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