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Frequently Asked Questions (FAQ)
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For a cylinder, the load direction could be defined locally in z, but for a hopper, the load would no longer be parallel to the XY plane.
Therefore, such a load must be divided into two components (X and Y), with the "Global related to the projected area" load direction, once XP and once YP, as well as the "Linear in Z" load distribution, see the image:
The load value may have to be converted.
The "temperature difference" load type always refers to the cross-section height in RFEM and RSTAB. For a rib, however, the plate component is not taken into account for the determination of the cross-section height, which is necessary for the determination of the load size. Therefore, the rib requires to define the loads for the member and the surface separately.
- Cross-section rib → rectangle 200/200
- Surface thickness → 200 mm
- Temperature difference between the top and the bottom of the component = 200 K.
Result for the deformation when modeling the component as a T‑beam (cross‑section)
The load for the model using surfaces and rib may be composed as follows:
The temperature load of the surface is also determined according to this scheme.
In the attached model file, there are two further modeling variants, in which the temperature distribution for the plate component was designed in more realistic way. The deformations in these two model variants are slightly larger for this example than in the other models.
In the background, the profile of the turbulence intensity over the altitude is a pure factor function depending on the altitude. By multiplying the altitude-dependent factors by the entered turbulence intensity, the turbulence intensity profile applied at the wind tunnel entrance results.
The generic turbulence intensity profiles from the RFEM 5 or RSTAB‑8 environment are each referenced to the bottom edge of the wind tunnel. Therefore, the factor function at this ground location has the value of 1, and thus defines the unmodified input value of the turbulence intensity at this location. At a higher position with a factor ≠ 1, the turbulence intensity input multiplied by this factor is applied accordingly.
Yes, this is possible in RFEM. However, you have to disconnect the generated load first. The generated loads are then converted into normal member loads and can be changed as required.
After disconnecting the generated loads, you can define the load eccentricity.
As expected, the member loads generate a torsional moment if they act eccentrically to the shear center.
The options for RSTAB are described in FAQ 2361.
Perhaps is the calculation of the corresponding load case deactivated in RFEM/RSTAB, see the image.
After you activate it correspondingly, the load case should be available for selection in the add-on module.
No, the load generation, such as "Surface Load on Members via Plane" only works for straight or articulated straight members.
If necessary, curved members can be converted into polygonal members as follows:
- Divide the curved member by the desired number of intermediate nodes
(right-click the member → Divide Member).
- Select all curved members.
- In the table, change the line type from "Arc" to "Polyline."
- If necessary, use the "Show Selected Objects Only" function, see Image 01.
- Change the top line type in the table.
- Select all rows → right-click → "Set", see Image 02.
- Generate the loads.
- Divide the curved member by the desired number of intermediate nodes
A temperature load is a surface load type, and is therefore applied like all other surface loads. To do this, it is necessary to first get the interface to the model, then to the loads, and then to the special load case:Sub surface_temp_load_test()' get interface from the opened model and lock the licence/programDim iModel As RFEM5.IModel3Set iModel = GetObject(, "RFEM5.Model")iModel.GetApplication.LockLicenseOn Error GoTo eDim iModelData As RFEM5.IModelData2Set iModelData = iModel.GetModelDataDim iLoa As RFEM5.iLoadsSet iLoa = iModel.GetLoadsDim iLc As RFEM5.ILoadCaseSet iLc = iLoa.GetLoadCase(1, AtNo)Dim surfLoad As RFEM5.SurfaceLoadsurfLoad.no = 1surfLoad.Type = TemperatureTypesurfLoad.Distribution = UniformTypesurfLoad.SurfaceList = "1"surfLoad.Magnitude1 = 10surfLoad.Magnitude4 = 40iLc.PrepareModificationiLc.SetSurfaceLoad surfLoadiLc.FinishModificatione: If Err.Number <> 0 Then MsgBox Err.description, , Err.SourceSet iModelData = NothingiModel.GetApplication.UnlockLicenseSet iModel = NothingEnd Sub
For a constant temperature load, the parameters Magnitude1 and Magnitude4 are used, where Tc is Magnitude1 and dT is Magnitude4. If a variable load is applied, Magnitude2 and Magnitude3 are used for the other corner points for Tc, and Magnitude5 and Magnitude6 for dT.
Currently, there is not the available option to apply the manually adjusted wind tunnel dimensions to all wind load cases. This option is currently in development for a future update release.
In the calculation parameters of the load combinations, the calculation type according to the second-order analysis is preset by default. For example, the calculation is performed according to EN 1995‑1‑1, 2.2.2(1)P, using the design values of the stiffness property of the structural component, that is, the stiffnesses divided by the partial safety factor. For this reason, this stiffness modification is activated by default (see Image 01). For the load combinations in the serviceability limit state, there should be no reduction of the stiffness, of course.
Manual Creation of Load Combinations
If you create the load combinations manually, the load combination cannot "know" which limit state is involved. In this case, it is necessary to make the setting manually (see Image 02). This setting must also be deactivated manually when switching to the geometrically linear analysis.
Automatic Generation of Load Combinations
If the load combinations are generated automatically by the program (see Image 03), the stiffness reduction is automatically deactivated for the SLS combinations specific to timber structures. For the ULS combinations, the reduction depending on the method of analysis is considered (second-order analysis and higher) or not (geometrically linear analysis). However, this requires the definition of the calculation type in the combination expressions (see Image 04). Changing the calculation type in the calculation parameters of the CO has no impact on the stiffness.
The reason there is a difference in results between superimposing LCs in COs vs. RCs is because when you apply the loads at once in a CO you will receive a different load distribution throughout the entire structure compared to the RC where the results are what are being added together. This is based on FEA where adding all of the loading together is different compared to solving the LCs each individually and adding the results together. Can be compared to a different order of operations to put it simply. You can see the comparison in the two figures below. Figure 1 is the load cases added up in CO1 and figure 2 has the LCs added together in RC1.
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Wind Simulation & Wind Load Generation
With the stand -alone program RWIND Simulation, you can simulate wind flows around simple or complex structures by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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