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Frequently Asked Questions (FAQ)
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The FE analysis determines the results for each FE mesh node. Usually, a continuous distribution of the internal force or deformation is preferable for the graphic. For this purpose, it is necessary to smooth the results e.g. by interpolation. However, the question can not be answered universally, because it has to be decided from model to model. Basically, RFEM distinguishes between the following five options:
There is already an interesting technical article about this topic.
- Constant on elements
constant distribution in the element
Interpolation in element based on results in special points
- Continuous within surfaces
Mean value mode at the node within the defined surfaces, followed by interpolation via the element
- Continuous total
All results are averaged on the node (independent of the defined surfaces); subsequently, the interpolation takes place via the element
- Continously by groups
It is also possible to smooth results by groups. RFEM provides Generated groups with similar material properties. You can create user-defined groups of surfaces or solids by using the navigator shortcut menu (right-click User Groups).
- Constant on elements
In order to optimize or minimize all processes in general for larger models, attention should be paid to various points. It can be an advantage if
- the wireframe model is used instead of the filled model in the graphic
- the table and navigator displays are deactivated,
- our programs are added to the exceptions in the settings of the antivirus program,
- as few applications and RSTAB / RFEM files as possible are opened at the same time,
- the PC is upgraded. For example, you can often achieve a significant increase in performance with SSD memory. The PC should also have sufficient random access memory.
It may also be advantageous to save the RSTAB / RFEM files locally instead of in a network.
It may also be due to missing user rights if the program reacts slowly. If you are not working under an administrator account, the user must have full access rights to different directories and subdirectories.
Furthermore, you should pay attention to always work with the current version of RSTAB / RFEM.
- the wireframe model is used instead of the filled model in the graphic
When calculating a result combination, I receive the "Warning No. 30014 – Incorrect addition of load cases in the result combination! The result combination contains load cases or load combinations with results containing second-order effects, which points towards nonlinear relationships and therefore cannot be added together..." What does this warning mean?
This warning appears in the case of the following result combination definitions when the load cases/load combinations are analyzed according to a nonlinear analysis such as second-order or large deformation analysis.
Case 1: RC = LC1/CO1 + LC2/CO2
For Case 1, load cases/load combinations cannot be superimposed together in a result combination when each case/combination is ran according to a nonlinear analysis such as a second-order (P-Delta, p-delta) or large deformation analysis. Deformations in both load cases are based on different structural systems and will result in incorrect results as P-Delta effects cannot be simply added together.
The solution for this case is to either run the load cases/load combinations according to a geometrically linear analysis where the results can be superimposed together in a result combination, or the consideration of the combined load cases must only be considered under the Load Combinations tab and evaluated individually rather than in a result combination.
Keep in mind, this same warning will appear when creating a result combination in a model where geometric nonlinearities are also defined. An example includes a slab foundation where a nonlinear surface support is defined to fail in the case of uplift. Geometric nonlinearities can accurately be considered in load combinations opposed to result combinations which may yield incorrect summary results.
Case 2: RC = factor* LC1/CO1 or factor* LC2/CO2
For Case 2, if a load case/load combination is calculated according to a nonlinear analysis, it is not possible to additionally apply a factor to the result combination. The factor would not only be applied to the defined loads on the structure, but also to the nonlinear effects such as P-Delta which is incorrect.
The solution for this case is to either run the load cases/load combinations according to a geometrically linear analysis where the factor can be applied to the result combination, or the factor can be considered under the Load Combinations tab where it will be applied directly to load cases only according to a geometrically linear analysis without consideration to the second-order effects
It is always necessary to use the member orientation and member rotation when defining the columns consisting of several single members. Some members have the x-axis directed upwards or rotated (see Figure 1). Due to the different orientations, the sign changes for My or Mz.It is very easy to check these settings by activating the display of the member axis systems (see Figure).
Transfer of internal forces from RSTAB or RFEM to SHAPE-THIN is only possible with the administrator rights. It is unfortunately not possible to grant access only for specific folders, etc., as this process intervenes more deeply in the operating system.
However, it is also possible in SHAPE-THIN to import internal forces from RSTAB/RFEM without activating the "Import Results from RSTAB/RFEM" function. The following options are available:
Insert internal forces via the clipboard
- In RSTAB/RFEM, you have to select and copy the corresponding internal forces in the table (see Figure 01).
- In SHAPE-THIN, you can enter the internal forces in the table (see Figure 02)
Insert internal forces via Excel
- The internal forces can be exported to Excel in RSTAB/RFEM. If you only want to export single tables, you can use the Excel button in the table toolbar to open the function. To transfer several tables to Excel at once, use the menu option File → Export. The relevant tables can then be selected in a dialog box. In Excel, you have to adjust the order of the table columns to the column arrangement in SHAPE-THIN (see Figure 03).
- In SHAPE -OVER, you can then use the "Export/Import of Table" function by using the Excel button in the toolbar of Table "3.1 Internal Forces" (see Figure 04).
- In the dialog box (see Figure 05), select the option "Import Table" and the setting "Import Table from Active Workbook". Before starting the import, the Excel Workbook has to be opened. If the "Import Table from Active Workbook" check box is not set, RFEM imports the worksheet with the name "LC [LCNo.] - 3.1 Internal forces".
In the graphic, only absolute values for the shear stresses are displayed. In the results table of SHAPE-THIN, you can also display the individual values. There, they are then displayed correctly with a sign.
You can create a curved beam in RSTAB by using the "Arc" function. For this function open Generate Model on the Tools menu.
When creating User-Defined Toolbars, always pay attention that no commands are moved to the standard toolbars and menus. These tables are always overwritten when installing the program for reasons of updating. The user-defined toolbars and menus are compatible and remain after an update.In the "Configuration Manager" dialog box, you can use the "Export Configuration as File" option to save the entire setting including all other objects (colors, options, borders, etc.).
The online service "Snow, Wind and Seismic Zones" graphically displays structural loads according to the standards of relevance to the user on the Google Maps tab and shows the site-specific structural loads for an explicit location on the map.Based on the national references of the standards used, the online service provides information about each of the load types described in the standard. If the standard specifies no data for a specific load type, the online service does not provide any further information for this load type (e.g. snow loads in the African desert).If a particular structural load standard is not offered in the Online Services selection boxes, this standard is not yet incorporated. Our team strives to expand the online service for all relevant countries around the world and to maintain the portfolio. The implementation priorities are geared to the needs of the user and the mandatory maintenance and renovation work.
In a 2D model XY with the degrees of freedom (uz/fx/fy), it is not possible to define an eccentricity. An eccentricity usually results in a normal force that is not covered by these degrees of freedom.
Use caution when using ribs. In contrast to the 3D model, the effective width also changes the stiffness of the structure.
It is therefore generally better to calculate beam models in a 3D model.
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