The calculation of my model results in unrealistically high stresses in some places. What could be the problem?

Answer

The most common causes are listed below:
1. Singularities 
Singularities appear in a limited range due to a concentration of the stress-dependent result values. They are conditioned by the FEM methodology: Theoretically, the stiffness and/or the loading in infinite magnitude are concentrated on an infinitesimally small area. Singularities therefore occur, in particular, at punctiform supports, load application locations, reentrant corners, or in the area of stiffness changes.

If the result value of the stress peak is larger and the area of this stress peak is smaller for a finer FE mesh, a singularity is very likely to occur.


When handling singularity locations it is recommended to follow articles of our Knowledge Base:
2. Unrealistic support definition 
Rigid supports (infinitely stiff supports) are rather unrealistic in many cases. Therefore, it is recommended to display the supports as elastic supports. In this case, the stiffness of adjacent structural components should be estimated realistically.


The deformation diagram, possibly with a pronounced precamber, and the output of the support reactions or contact stresses are suitable for checking purposes. For a better overview, the simplest possible loads should be used for the check.
 
Often, a mistake in the direction definition, for example of loads, member hinges, or line and surface releases, is the cause of unrealistic behavior. When using local or rotated coordinate systems as reference systems, particular attention must be paid to the correct definition. For example, nonlinearities defined in the opposite direction are typical for supports that fail due to tension or compression.
Incorrectly defined loads can be easily identified by displaying the loading. The loads applied for the calculation can be conveniently displayed in the Results navigator by using the "Load Distribution" option.

 
Furthermore, modeling inaccuracies can lead to incorrect definition of directions. By importing a DXF file, you can introduce inaccuracies into the model, for example, nodes that are not on top of each other or lines skewed in the wrong direction.
The function "Regenerate Model" is very helpful for the treatment of minor inaccuracies.


Incorrectly defined releases and hinges can usually be identified by means of the deformation graphic and the diagrams showing the distribution of internal forces. Again, it is recommended to work with simple loads for checking purposes.
4. Model does not correspond to reality 
Often it can happen that not all external or internal influences from a structure to be modeled have been considered sufficiently and accurately in the model. Supports or supporting structural components may not have been modeled or it happened in the wrong place. The realistic estimation of the stiffness of adjacent structural components is also important. Provided that it has been over- or underestimated, the load transfer in the model is sometimes significantly changed.


However, a simple check of the deformation, possibly with a pronounced precamber, is possible.
The following questions may help to find a solution if the real structure is known: Is the magnitude of the deformations realistic? Is the deformation diagram qualitatively consistent with my expectations?


A good example is presented in the following Knowledge Base article:

Keywords

Model Reality Support Internal force Structure Deformation

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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

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