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Frequently Asked Questions (FAQ)
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AnswerA suspended, linearly supported membrane roof structure can be modeled in RFEM using the RF‑FORM‑FINDING add-on module. For this, define as follows:
- Load-bearing structure around the membrane roof
- Boundary elements of the membrane consisting of cable elements with the corresponding form-finding settings
- Membrane between the boundary elements with the corresponding form-finding settings
- Support boundary conditions for transferring the loads
- Load case with the "Form-finding" action category to describe the form-finding loads in addition to the prestress
To delete elements, there is the "DeleteObjects()" function in the model data interface. Deleting all members is then as follows:Sub test_delete_objects()Dim iApp As RFEM5.ApplicationSet iApp = GetObject(, "RFEM5.Application")iApp.LockLicenseDim iMod As RFEM5.IModel3Set iMod = iApp.GetActiveModelOn Error GoTo e' get interface for model dataDim iModData As RFEM5.IModelData2Set iModData = iMod.GetModelData' get all membersDim mems() As RFEM5.Membermems() = iModData.GetMembers' create member listDim mem_list As StringDim i As IntegerFor i = 0 To UBound(mems, 1)mem_list = mem_list & mems(i).no & ","Next' delete membersiModData.PrepareModificationiModData.DeleteObjects MemberObject, mem_listiModData.FinishModificatione:If Err.Number <> 0 Then MsgBox Err.description, vbCritical, Err.SourceiMod.GetApplication.UnlockLicenseSet iMod = NothingEnd Sub
Please note that the "DeleteObjects" function only works with the object number and not with the object index. These numbers are transferred as a string, separated by commas.
For this reason, all members had to be fetched first. Then the member field was looped through and all member numbers were entered in the string.
AnswerA tent roof with two cone tips can be modeled in RFEM using the RF‑FORM‑FINDING add-on module. For this, proceed as follows:
- For each conic area, generate a separate membrane surface around the larger boundary line.
- Integrate the opening of the cut cone tips into the base areas.
- Align the axis systems of the respective conical membrane surfaces to the center line.
- Define the "Projection" form-finding method for the conical membrane surfaces.
- Support the membrane edges sufficiently and start the form-finding process.
AnswerIn this case, the program asks if you want to create a hole in the surface and place a new surface in it. The surfaces will be rigidly connected, unless the boundary lines include line releases, for example. This arrangement is suitable for heads in a ceiling slab. You can enter a larger thickness for the inserted surface, and thus consider the larger thickness of the head.If you do not integrate the surface, the surface will be doubled at the corresponding location. If the surfaces remain in one plane, the boundary lines will be integrated, and thus the finite element mesh will be interconnected, but only at the location of the lines. Assuming the same surface thickness, the result of the interaction is negative due to the added weight.
Perhaps the input parameter for the surface is missing. In the model file of the FAQ, the axis of the surface refers to a line that has obviously been deleted before. Thus, it is not clear how to create the axis system for the surface.
There are two simple solutions:
- Select a line to which the x- or y-axis should be parallel.
Image 02 - Definition of Axes
- Switch back to the default setting.
- Select a line to which the x- or y-axis should be parallel.
The minimum of the entered shear reinforcement can be controlled by two settings:
- Window 1.4 - Reinforcement Ratios - Minimum Shear Reinforcement Ratio
- Window 1.4 - depending on the standard, for example, for DIN EN 1992-1-1 - Minimum Shear Reinforcement
Please note that the minimum shear reinforcement according to DIN EN 1992‑1‑1 refers to the width-height ratio of the entire slab. Since RF‑CONCRETE Surfaces is suitable for any surfaces and the individual FE elements are designed, this ratio must be determined and entered manually.
AnswerThe suggested default wind tunnel dimensions of the intake size are set to twice the width and height dimensions of the model. Its length is set as three times the model length with a shorter distance at the intake side.The procedure used to calculate the default wind tunnel dimensions involves complex testing process that has been optimized. The default dimensions are determined as to provide sufficiently large free space around the structure in the model, and also set as small as possible to obtain short calculation times.Although the automatic default dimensions should be sufficient, manual changes can be made by the user.
A drilling can be performed with a surface model. For this, it is first necessary to split the member (the finer is the division, the more accurate is the result) and then generate surfaces from it.
The resulting cross-section outlines can then be easily rotated. Please note that the cross-section shortening is not taken into account. The RF‑IMP add-on module provides more accurate results as it can pre-deform the FE mesh.
AnswerIn the Program Options menu, under Program tab, you can check the "Combination description according to action category" to display "D, L, W" instead of "LC1, LC2, LC3."
Yes, you can do this very quickly by using Tools → Generate Cutting Patterns from Cells.
This feature allows you to define which surfaces should be used and whether to ignore some lines.
You can then make further settings for the created cutting patterns as usual. It is possible to select the cutting patterns in the project navigator as well as graphically.
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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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