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Frequently Asked Questions (FAQ)
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The following values represent the upper limits in the data structure of RFEM:
- 99,999 structural data (objects of each category, that is nodes, lines, surfaces, cross-sections, etc.)
- 99,999 loading data (objects of each type of load per load case)
- 9,999 load cases
- 9,999 load combinations (the sum of the nonlinearly analysed load cases and load combinations may not be higher than 9,999)
- 9,999 result combinations
Please note that the limit for efficient worki with RFEM may be lower and may also depend on the hardware.
The export is not possible in this direction.
In RFEM, surface elements may be available in addition to member elements. RSTAB is not able to import these surface elments because this would lead to a falsification of the structural system and so to wrong results.
When you enter models in two-dimensional space, only angles of rotation of the cross-sections of 0 ° and 180 ° are allowed. The direction of the local axis system in member (xyz) is clearly defined, and for 2D models, only member internal forces M y and V z are calculated.
In a two-dimensional space, the strong axis of the cross-section (y-axis) is always aligned in the direction of the global axis Y, the weak axis (z-axis) is not considered (assumed as completely non-deformable, so to speak).
If cross-section rotations are allowed, double bending might occur because only loads in the 2D zone can be defined in the XZ plane. However, the resulting Vy, T, and Mz component would then remain unconsidered. For this reason, only those cross-section rotations are allowed for which the local z-axis of the cross-section points into the XZ plane.
Finally, in this case, we recommend entering a 3D model where any cross-section rotations are allowed.
Background: Each surface has a local coordinate system in RFEM (x,y,z).
The coordinates x and y are in-plane, z runs perpendicular to the surface.
The top and bottom side of a surface is determined by the direction of the z-axis.
The direction of the local z-axis determines the bottom side of a surface. Usually, this local z-axis is orientated downwards. Depending on the defined direction of the boundary lines and the sequence in which the lines were clicked., it is also possible that the local z-axis points upwards.
It is easy to correct this. First, display the local surface coordinate system.
To do this, proceed as follows:
Go to the "Display" navigator on the left. Here, you can set all display properties in a tree-like structure.
Open the entries "Model" -> "Surfaces" and select the "Surface Axis Systems x,y,z" check box.
The bottom reinforcement is on the side of the slab, where the z-direction is positive.
To reverse the direction of the local z-axis, click the corresponding surface, and then select the "Reverse axis system" option in the context menu.
You can find the latest graphics card driver on the website of the graphics card producer.
Please note that the newest graphics drivers must fit the operating system. A driver which was developed for windows XP, for example, cannot be used under Windows 8.
On the corresponding website, there is usually a link "Driver" or "Download."
First, read the installation instruction. Select the model of the graphics card and of the operating system. After these specifications, you can usually download an executable file.
Save the file in any folder, and run it after the download.
Some manufacturers (for example, Nvidia), offer only one driver for different models of graphics cards.
The OpenGL accelerator can be generally used for the color depth of 16-bit or 32-bit only.
In the Display Properties of Windows, set the color depth to True Color (32-bit) or to High Color (16-bit).
The calculation can be terminated due to an unstable structural system for various reasons. There can be a "real" instability due to overloading the system, but the instability effects may also be caused by failing members.
In the calulcation parameters, you can deactivate the nonlinearity "Members due to member type" (see Figure 01). If the calculation is then possible without the error message, the problem is probably caused by failing members.
The option "Failing members to be removed individually during successive iterations" in the Global Calculation Parameters dialog box (see Figure 02) allows you to prevent the complete failure of tension members. This will help in most cases. For this, the number of possible iterations should be sufficiently large.
An alternative method is to apply a prestress to the tension members in order to prevent the failure of them.
The values for the precamber are not shown because the ordinate of the buckling mode is probably too small so that it cannot be considered by using the specify tolerance.
In the "Details" dialog box, you define from which ordinate of the selected buckling mode or deformation the imperfection is to be generated.
Yes, you can plot directly from RSTAB or RFEM. You can do this by sending the image directly to a network plotter or to a local plotter, provided that this plotter is installed as Windows printer.
Select the graphic that you want to plot and click [Print]. Specify the following in the "Graphic Printout" dialog box: In the "Graphic Picture" section of the "Graphic" tab, select the "Directly to a printer" option. In the same tab, select in the "Graphic Size" section the "Window filling" option.
By clicking [OK], you open the "Print" dialog box, where you can set the installed printer or plotter. In the properties of the driver, you can specify the paper size.
Alternatively, you can plot from a file. To do this, select in the "Print" dialog box the "Print to file" check box. A .prn file is created. If you rename the file format to .hgl, you can import it in an image editor and send it to a plotter.
Compressive forces in cables or tension members may arise if the number of iterations is not sufficient for this analysis so that the system did not converge. The number of iterations can be specified in the Global Calculation Parameters tab of Calculation Parameters (see figure).
For the maximum number of iterations, the value 100 is preset. However, this does not mean that all iterations will be run. Depending on the structural system, the calculation often converges much earlier.
Check also the settings of Reactivation of Failing Members. If the option "Assign reduced stiffness to failing members" is selected, small compressive forces may arise.
If this is not justifiable, select the option "Failing members to be removed individually during successive iterations." However, you should pay attention to the sufficient maximum number of iterations (see above).
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