Question
The calculation of my model results in unrealistically high stresses at many locations. What could be the reason for this?
Answer:
The most common causes are listed below:
Singularities occur in a limited area due to the concentration of stress-dependent result values. They are conditioned by the FEM methodology: In theory, the stiffness and/or the stress in an infinite size will concentrate on an infinitesimally small area. Therefore, singularities occur especially at point supports, load application locations, reentrant corners, or in the area of stiffness peaks.
If the result value of the stress peak is greater and the area of this stress peak is smaller in the case of a finer FE mesh, a singularity is very likely to occur.
The recommendations for dealing with the singularity locations are included in the following technical articles of our Knowledge Base; for example:
Rigid supports (infinitely stiff supports) are rather unrealistic in many cases. Therefore, we recommend displaying the supports as elastic supports. In this case, the stiffness of the adjacent structural components should be estimated realistically.
For checking purposes, the deformation diagram is suitable, possibly with a stronger precamber, as well as the result display of the support reactions or contact stresses. For a better overview, the simplest possible loads should be used for the check.
A mistake in the direction definition, for example, of loads, member hinges, or line and surface releases, is often the cause of unrealistic behavior. When using local or rotated coordinate systems as reference systems, you must pay attention 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 identified easily by displaying the loading. The loads applied for the calculation can be displayed easily in the Results navigator using the "Load Distribution" option.
Furthermore, modeling inaccuracies can also lead to the 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 directions.
The "Regenerate Model" feature is very helpful for treating minor inaccuracies.
Incorrectly defined releases and hinges can usually be identified by means of the deformation image and the diagrams of internal forces. Again, we recommend working with simple loads for checking purposes.
It can often 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 they are in the wrong place. The realistic estimation of the stiffness of the adjacent structural components is also important. Provided that it has been over- or underestimated, the load transfer in the model is sometimes changed significantly.
However, it is possible to simply check the deformation, possibly by using a stronger precamber.
The following questions may help you to find the solution if the real structure is known: Is the magnitude of the deformations close to reality? Is the deformation diagram qualitatively consistent with my expectations?
A good example is presented in the following Knowledge Base article:
Do you have any questions?
Using the Timber Design add-on, timber column design is possible according to the 2018 NDS standard ASD method. Accurately calculating timber member compressive capacity and adjustment factors is important for safety considerations and design. The following article will verify the maximum critical buckling strength calculated by the Timber Design add-on using step-by-step analytical equations as per the NDS 2018 standard including the compressive adjustment factors, adjusted compressive design value, and final design ratio.
The three types of moment frames (Ordinary, Intermediate, Special) are available in the Steel Design add-on of RFEM 6. The seismic design result according to AISC 341-22 is categorized into two sections: member requirements and connection requirements.
The fatigue design according to EN 1992-1-1 must be performed for the structural components subjected to large stress ranges and/or many load changes. In this case, the design checks for the concrete and the reinforcement are performed separately. There are two alternative design methods available.
The Steel Design add-on in RFEM 6 now offers the ability to perform seismic design according to AISC 341-16 and AISC 341-22. Five types of seismic force-resisting systems (SFRS) are currently available.
In the ultimate configuration of the steel joint design, you have the option to modify the limit plastic strain for welds.
Using the "Base Plate" component, you can design base plate connections with cast-in anchors. In addition to plates and welds, the design analyzes the anchorage and the steel-concrete interaction.
In the "Edit Section" dialog box, you can display the buckling shapes of the Finite Strip Method (FSM) as a 3D graphic.
Do you have individual column sections and angled wall geometries, and need punching shear design for them?
No problem. In RFEM 6, you can perform punching shear design not only for rectangular and circular sections, but for any cross-section shape.
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