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Frequently Asked Questions (FAQ)
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AnswerIf you define line loads on a line that is decoupled from the overall system, that line becomes compliant. The program checks this incorrect entry and gives a hint (Fig. 1). However, there are structures where this line is kept at a different point. In this case, the program continues to calculate after the user has confirmed the note. However, since the deformation for such a decoupled line becomes very large, it is not displayed in the graphic output.We generally recommend not to load lines that are decoupled via a line release or line joint.The theoretical background will be explained in this article .
The easiest way to find the internal forces at these nodes is to print the pictures of members into the printout report.
If this solution is not an option, you can also find the values in the result table 4.1 in the printout report. Since the extreme values are only activated by default, it is still necessary to activate nodal values in the selection.
It is usually not reasonable to include the internal forces of all member in the printout report. Therefore, you can only select the members that are relevant to you.
Designs in our module RF-/JOINTS Steel - Rigid are based on the assumptions and regulations of the standard EN 1993‑1‑8. Here, bending from the main beam plane is not considered.
In RFEM, it is possible to model any rigid joint. All internal forces can then be taken into account.
RF-JOINTS performs an idealized design of a steel connection according to the standard, which cannot be easily compared with an exact FE calculation.
Thus, the following conditions must be met:
- Consideration or exclusion of friction/compression/tension within the contact solid (tab 'Solid') as well as for the bolts modelled subsequently
- Consideration of internal forces and deformations within the subsequently modelled end plates or similar, which causes redistribution of bolt forces in the FE calculation (in contrast to the idealized design in RF‑JOINTS)
This can be corrected by rigid connection objects, for example (an end plate as a rigid surface).
- Uniform load introduction into the FE model, for example, by using rigid members or rigid surfaces as described in the article 'FEM Modeling Approaches of Rigid Connections'
AnswerIn such a case, one should first look at the distortions. It is often the case that the bars at the junctions were not properly connected (minimal inaccuracies). Due to the unrealistic large resulting twists around the rod axis then arise these moments.
AnswerOften, for example, it helps to size and choose the means of connection between 2 surfaces, knowing the resultant of the results between the surfaces. The resultants for the results of line joints and line releases can be displayed via the Project Navigator results in the section "Approvals" (see Figure 1).
The easiest way to explain the differences is to use an example (see Download -> Example file). This contains the result of the comparison of non-linear calculation to linear calculation (see also Figure 1).
The left model and the middle model have linear line joints. The left model defines a compliance in u_x and u_y. At the middle model "only" in u_x direction. On the right model, the compliance is defined in u_x and u_y. However, a pressure contact between the surfaces is defined here. These surfaces can not penetrate to pressure.
If you look at the results, you can see that the left model is too soft, because the surfaces penetrate in the u_y direction because of the softness. The middle and right models, on the other hand, give identical results.
Often it makes sense to stay as linear as possible, so the middle model is probably the most appropriate for numerical investigations. Even if the right nonlinear model represents reality even better. However, the example is only a small comparison model. In reality, one probably does not use the spring in u_y / u_z, but assigns this force to a tie rod. That's why it's better to use the middle model without u_y.
The consideration of the flexibility between surfaces is also discussed in the following technical contribution of our knowledgebase:
AnswerFirst, select the National Annex "DIN" in the "1.1 General Data" window. Then, open the [Details...]. A dialog box opens where you can find the design for limiting the gaping joint which is described as "Highly eccentric loading in the core". See Figure 01.
RF-/JOINTS is divided into several joint groups. Each of these joint groups requires a separate licence key. If RF-/JOINTS detects a key, the joint group is marked with a green circle (see Figure).
In your case, you have probably selected a joint group that is not licenced. Therefore, please set the joint group that you have purchased. The message about the demo version should then disappear.
Line joints can be efficiently assigned using the function "Assign to lines graphically" (see Video 1 Graphically assigning line joints) You can call the function via the menu "Insert -> Model data -> 1.10 Line joints -> Assign to lines graphically" (see Fig 1 graphically assign line joints).
Video1-en.wmv (1.41 MB)
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