The structural analysis software RFEM 6 is the basis of a modular software system. The main program RFEM 6 is used to define structures, materials, and loads of planar and spatial structural systems consisting of plates, walls, shells, and members. The program also allows you to create combined structures as well as to model solid and contact elements.
RSTAB 9 is a powerful analysis and design software for 3D beam, frame, or truss structure calculations, reflecting the current state of the art and helping structural engineers meet requirements in modern civil engineering.
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To perform an earthquake analysis, you need a modal analysis and then a load case of the Response Spectrum Analysis type.
After you have performed your modal analysis, create a new load case. Here you will find the usual settings from the previous program generation.
In the Response Spectrum tab, you can define your response spectrum as usual. If you want to use a response spectrum according to the standard, make sure that the desired standard is selected in the general data of Standards II.
In the Selection of Modes tab, you can select the mode shapes and filter them, if necessary.
After the load case has been calculated, you obtain the results.
Masses can be neglected in the modal analysis settings.
It is possible to neglect masses in all fixed nodal supports and line supports, or to create a selection of the individual objects.
Yes, you can also export the response spectra from RFEM 6 and import them into RFEM 5 as a user-defined response spectrum. Please note that export and import via Excel may also have different columns/descriptions due to different versions.
Export your data in RFEM 6 to Excel.
If you want to import this table directly, you will get an error message. RFEM 5 expects a different worksheet description and two columns only.
As soon as you adjust the name in Excel and delete the column with the frequency results, you will be able to edit the response spectrum in RFEM 5.
There can be many reasons for unstable structural systems. The best way to determine the reason for this message is to use the Structure Stability add-on.
Structure Stability Add-on
This add-on allows you to calculate your structure without loading, and thus to perform an instability analysis using the mode shape.
Therefore, you can display the unstable shape of your structure.
As you can see in our example, the upper steel beams are subjected to lateral deflection.
Upon closer inspection of our modeling, we recognize that we have unconsciously created a hinge chain from couplings of the Rigid-Hinge type. If we remove this hinge chain, we can calculate the load case.
A calculation break‑off due to an unstable system can have different reasons. On one hand, it can indicate a "real" instability due to overloading the structural system; on the other hand, modeling inaccuracies may also be responsible for this error message. In the following text, you can find a possible procedure for finding the cause of the instability.
1. Modeling Check
2. Check of Stiffening
3. Numerical Problems
4. Detecting Causes of Instability
This is not possible in RFEM 5 or the RF‑STAGES add-on module. However, it is possible in the new program generation. In the Construction Stage Analysis add-on for RFEM 6, you can now modify the properties of structural elements.
The warping of a cross-section can be displayed in the "full mode". For this, it is reasonable to increase the display factor for torsional warping in the control panel; see Image 01.
Furthermore, you can select the value of the local deformation ω [1/m] in the Results navigator; see Image 02.
The warping stiffness can be deactivated by cross-section in the "Edit Cross-Section" dialog box; see the image.
Both support forces and loads are assumed for the calculation with warping torsion in the centroid. Accordingly, an asymmetric cross-section would automatically receive torsion; see the image.