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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The Building Model and the feature of modeling stories with "Rigid Diaphragm" is not designed for all building types.
The function was primarily developed for 3D buildings with 5-10 stories (or more) with a regular or the same floor plan. This means that you should only assign the "Rigid Diaphragm" function to the slabs where the walls and columns are positioned identically in the stories above and below. If this is not the case, instability may occur.
If the model has been entered correctly according to this convention, three options for the result display will be available to you:
The "Total" result display shows the results on the entire vertical components (that is, walls, shear walls, columns, and so on). See Image 02. If you select "Floors only", the results for the separate calculation of slabs are displayed as a 2D model. The "Combination" option corresponds to the same results from both result types mentioned above.
For smaller 3D models and buildings with different floor plans, it is still better to work with the usual modeling as a 3D model. If you are working with models that sometimes have regular floor plans, you can alternatively assign the "Rigid Diaphragm" option to the individual floor slabs. The floor plan geometry of the stories above and below this slab should then be the same again.
The fundamental extraction of a 2D floor from any 3D model is not possible with the technology implemented for this add-on function.
If no angle can be defined in the "Rotation" column, there is an isotropic material model selected for the material, where stiffnesses are identical in all directions and it is not necessary to define an angle.
If you use materials with anisotropic behavior (for example, timber), it is necessary to ensure that the "Orthotropic | Linear Elastic (Surfaces)" material model is selected.
Note: The "Orthotropic | Timber | Linear Elastic (Surfaces)" material model cannot be currently used in combination with the "Layers" thickness type.
As soon as switching to the orthotropic material model, the individual layers can be rotated accordingly.
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.
You can adjust the display of the mode shape normalization directly in the Results navigator. If the setting is changed, no recalculation is necessary.
Depending on the setting, the largest displacement or deformation represents the reference value 1, to which the other results are scaled.
You can also define structural modifications in a load case of the Modal Analysis type. Thus, you can access the stiffness modifications of the individual objects and deactivate the selected objects, if necessary.
In the modal analysis settings, you can set the minimum axial strain for cables and membranes in order to apply an initial prestress to the objects and thus improve the convergence of the calculation. The initial prestress is applied to the objects in a simplified approach.
If you compare this setting with a surface load of the Axial Strain load type, you should pay attention to the fact that the two approaches differ. With the surface load, you perform a calculation in such a way that the actual prestress can deviate from the specified prestress. The calculation also takes into account other boundary conditions, such as the Poisson's ratio of the material.
You can easily check this if you vary the Poisson's ratio of the material. A Poisson's ratio other than 0 causes the deformation to interact in the x- and y-directions of the surface, which no longer results in a constant stress/strain over the entire surface.
If the Poisson's ratio is 0, you obtain the same results.
In order to display the mode shapes of your dynamic analysis, you have to create a load case of the Modal Analysis type and specify your settings for the modal analysis there.
After the calculation, you can evaluate your results in the Results navigator. You can see further information in the table.
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.