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Frequently Asked Questions (FAQ)
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AnswerIt is not possible to globally answer this question because it depends on the system. There are several divisions to be considered in RFEM.
1. Member divisions for results tablesYou can create member divisions for result values by using the menu 'Insert > Model Data > 'Member Divisions'. This division ensures that - e.g. in the RFEM results tables - the internal forces of members can also be displayed at intermediate points. The graphical output remains unaffected.
2. Member divisionsThe divisions for the graphical result diagram and the determination of the extreme value can be viewed and influenced in the FE mesh settings (see Figure 1).For cable, foundation, and tapered members or members with plastic properties, you can specify the number of internal divisions. They lead to a real division of the member by intermediate nodes. However, if a member is arranged on the boundary line of a surface or if the definition line has an FE mesh refinement, the specification has no effect.Select the 'Activate Internal Member Divisions for Large Deformation Analysis' option to divide also beams by intermediate nodes for the calculation according to large deformation analysis so that these members are calculated with higher accuracy. The number of member divisions is taken over into the input field above.If using the division even for straight members, which are not integrated into surfaces, FE nodes are generated on all free members and considered for calculations according to the linear static and second-order analysis. The length of the finite elements is either determined by the global target length l FE set in the General dialog section or entered manually.With the option 'Use Division for Members with Nodes Lying on Them', RFEM generates FE nodes on those locations of the member where end nodes of other members are lying, without having any connection existing between these members.
AnswerThe outputs of surfaces in RFEM refer to averaged internal forces. The design in RF-CONCRETE Surfaces is based exclusively on the internal forces, which have been averaged within a surface. Smoothing is not performed across the supported line. In this context, the shear force distribution shown in Figure 01 may occur.
Yes, it is possible. For this, you have to combine the members into a set of members. For continuously connected members, the type "Continuous Member" can be used. For other members, use the "Member Group". In principle, the distinction is only important for the subsequent design in add-on modules.After creating the sets of members and the structure, it is possible to output the internal forces in the result window "Sets of Members - Internal Forces" Use the filter of the tables to hide unwanted results.
The member internal forces (for example, the bending moment My) of the rib member are not only dependent on the defined member end releases, but also on the surface internal forces in the plate.When entering the rib, specify an integration width of the surface internal forces, please.The rib-related internal forces consist of the member internal forces which belong to the eccentrically connected rectangular cross-section and of the surface internal forces integrated over the integration width.Now, this means that you can get a bending moment My for a rib member, despite the input of member end releases, because the bending moment can originate from the integrated surface internal forces.In the Display navigator, you can specify whether the results including the portion from the surface internal forces have to be displayed (default setting).Or without the proportion of surface internal forcesIn order to get a 'Zero-Crossing' of the moment My in the rib member, it would be necessary to insert a line hinge in the area of the connection of the plate to the wall.
AnswerIn the fire resistance design, the acting internal forces are determined again if the thermal expansion of the concrete and the reinforcing steel and the precamber due to the temperature difference is taken into account (Figure 01).If the thermal expansions and the precamber are not taken into account, the acting internal forces should correspond to the internal forces of the calculation from RFEM or RSTAB (Figure 02).To what extent it is allowed to deactivate the thermal expansions and precambers has to be checked in connection with the underlying standard.
The difference between RFEM and RF-CONCRETE Columns is caused by the Result combination set to Max. values. If you switch to Min. or Max and Min. values, the same values are displayed as in the design module.
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
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".
To implement this in the program, you have to copy the "Temperature" load case (see Figure 01). All loads contained in the load case will be copied as well. One of the load cases is used for the Load Combinations for Ultimate Limit State (ULS), the other one for the serviceability limit state (SLS). The load in the load case for ULS is now multiplied by 1.0/1.5 = 0.667 (see Figure 02).
In order that the two load cases do not occur simultaneously, but only for the specific design situation, exceptions are determined in the respective combination rules. For ULS, it is quite simple to define the self-weight load case such that it is not combined with the Temperature User-Defined Case for SLS (see Figure 03). For SLS exactly the other way round, so load case dead weight not with temperature for ULS (see picture 04). The "Differently for each combination expression" check must be activated.
The desired load combinatorics is obtained subsequently (see Figure 05).
No, the basic reinforcement defined in RF-CONCRETE Surfaces is not considered in the determination of internal forces in RFEM. In RFEM, the internal forces are determined with the modulus of elasticity of the selected concrete. The reinforcement amount has no influence (linear-elastic calculation, state I).The situation is different if you perform a nonlinear design in state II in the serviceability limit state by means of the RF-CONCRETE NL add-on module. Here, you specify an existing basic reinforcement that you want to consider for the nonlinear calculation in state II. In nonlinear design (available only for SLS), the determination of internal forces is carried out with the effective stiffnesses (state II). Thus, the defined reinforcement has an influence on the internal forces.You can evaluate these internal forces (from state II influenced by the defined reinforcement) in the results of RF-CONCRETE Surfaces. See Figure 01 with the Results navigator of the RF-CONCRETE Surfaces add-on module.
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