Frequently Asked Questions (FAQ)

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• In RFEM, I would like to load a circular ring, which is displayed as a member, with the load generator. However, the curved member is not taken into account. Why is that?

New FAQ 004205 EN

The function [Generate Loads → From Area Load on Members via Plane ...] requires the defined plane to be created from a polygonal chain. If a curved member is created from arcs, the plane as a polygon can not find the outer contour of the arc, because it is only an approximation. In short, curved members can not be stressed by the load generator in RFEM.

In this case, it is recommended to display the curved member by means of several straight member segments. Thus, the polygonal chain can be traversed cleanly. In order to create the corner nodes of the polygonal chain more quickly, it is recommended, for example, depending on the number of member segments in Excel. The numbering of nodes is important. The procedure is shown in the video.
• How would you best model hold down elements within panels?

New FAQ 004201 EN

In a short overview, creating hold down elements involves modeling rigid links and adding in nodal supports with non-linearity settings that allows the supports to take only tension forces. A line support is added at the bottom of the wall that only takes compression forces. The individual nodal supports connected with rigid members only take tension forces.

A more detailed look on how these elements can be model can be seen in the video below.
• Why are there no resultant support forces for result combinations?

New FAQ 004200 EN

For a resultant, a concrete combination of loads is required, which result combinations can not provide.

The following example shows the problem quickly. A single-span beam is loaded with three different load cases. For the support at node 1, the result envelope of the 6 possible load combinations results in a maximum PZ of 11.25 kN from the result of CO 2 (see Figure 01). The support at node 2 has a maximum PZ of 12 kN from the result of CO1. However, the resultant of 23.25 kN does not occur in any of the involved load combinations and is therefore too large (maximum CO 1 and CO 2 with 22.5 kN).

The situation is similar with the pure result combination from the load cases, which have the same maximum values PZ of the nodal supports 1 and 2. However, it is not apparent here that a resultant would give incorrect results.

For result combinations, resultants are not used for result combinations because the results may be incorrect.

• How can I create an imperfection via the COM interface?

New FAQ 004199 EN

An imperfection is considered load and is transferred via the interface of the load case. Provided that the interface to the model has already been fetched, the interface to the loads (ILoads) is retrieved, followed by the interface to load case 1 (ILoadCase), if it has already been created:

'set loadcasesDim iLoads As iLoadsSet iLoads = model.GetLoads        'get load case.'Dim iLc1 As ILoadCaseSet iLc1 = iLoads.GetLoadCase (1, AtNo)        'define imperfectionDim imperf As Imperfectionimperf.Comment = "test"imperf.Direction = LocalZTypeimperf.Inclination = 200imperf.no = 1imperf.ObjectList = 1imperf.Precamber = 300imperf.PrecamberActivity = ActivityAccording_EN_1993_1_1        'set imperfection'iLc1.PrepareModificationiLc1.SetImperfection imperfiLc1.FinishModification

The data of the imperfection is then filled out first, here for member 1, and then transferred within a Prepare-/FinishModification block of the load case Interfaces.

• How can I create a circular opening in a pipe?

New FAQ 004196 EN

Creating the opening by means of an intersection

To create the opening, you have to create a surface with the diameter of the opening through the pipe wall. With the "Create Intersection" function, you can create individual components that you can deactivate afterwards. The procedure is shown in the video.

Creating the opening by means of a converted intersection line

It is also possible to convert the found intersection line into a normal line. Then, the intersection can be deleted and an opening can be put into it. The inserted opening then has to be integrated manually into the surface (see the video). Please note, however, that the quality of an intersection is of a higher quality than the converted intersection line. When using the converted intersection line, discontinuities may occur in the rendering or FE mesh, depending on the model.
• How can I retroactively change a member via the COM interface?

New FAQ 004195 EN

To modify an existing element, you have to get the interface to the corresponding element, here an example of a member:

Dim iModel As RSTAB8.modelSet iModel = GetObject (, "RSTAB8.Model")iModel.GetApplication.LockLicense    Dim iModData As IModelDataSet iModData = iModel.GetModelData    Dim iMem As RSTAB8.IMemberSet iMem = iModData.GetMember (1, AtNo)

Use this code to get the interface to member 1, which must already be created. Then, you can use the .GetData () method of the interface to get the member data.

If you want to modify data (such as the member rotation here), you can subsequently transfer it to the program within a Prepare-/FinishModification block with the method .SetData ().

Dim mem As RSTAB8.Membermem = iMem.GetData    mem.Rotation.Angle = 0.5mem.Rotation.Type = RSTAB8.Angle   iModData.PrepareModificationiMem.SetData memiModData.FinishModification
• When calculating an inclined plate, I receive very high result values for the line supports at 2 edge nodes. Why is this how it works and how can this be avoided?

New FAQ 004194 EN

The default definition of surface elements assumes an isotropic material behavior. The load attempts to get to the supports as quickly as possible. The stiffness of the elements also plays a role here.
The structural behavior or the load transfer is best represented and understood with the trajectories of the principal moments α b for plates. For wall elements, consider the trajectories of the principal axial forces α m .
In this example, the load is not applied parallel to the free plate edges but almost perpendicular to the supports, because this is the shortest path of the load transfer.
At the blunt corners of the system, the load application area is larger than in the support centers, corresponds to a singularity location and thus results in large peak values.
In order to force the system to remove the load parallel to free plate edges, the following procedure is the fastest:
Definition of an orthotropic plate. The "effective thicknesses" orthotropy type is recommended. Thickness of the actual plate thickness is specified in the support direction and a very small thickness (for example 1mm) in the secondary load.
The second graphic shows the difference between both models.
• Why are imperfections taken into account in RFEM and RSTAB when calculating according to the linear static analysis, even though no component deformations are considered according to the linear static analysis?

New FAQ 004193 EN

In general, an imperfection describes the imperfection of a structure or the deviation due to its production from the ideal shape. There are different ways to simulate the imperfection. In RSTAB and RFEM, imperfections are represented as equivalent loads. The definition of equivalent loads is shown in Figure 01 and is taken from [1] . The same is described in EC3 [2] . Since these are equivalent loads that are dependent on the axial force, they are also taken into account for a calculation according to the linear static analysis. It is recommended to manage loads and imperfections in separate load cases. They can be suitably combined with each other in load combinations. For the load case general data (see Figure 02), load cases with pure imperfection loads have to be classified as the action type "Imperfection".
• How is it possible to change the steel rebars sizes from the American Standard (#3,#4..etc) to millimetres in RF-CONCRETE Members while using ACI?

New FAQ 004192 EN

You will find an option in the "Settings" of the add-on module (see picture 01).
• When exporting the additional required surface reinforcement to REVIT, the displayed graphic in REVIT and RFEM does not match, how can I correct this?

New FAQ 004190 EN

In RFEM, the graphical results are smoothed on the basis of the results at FE mesh points. The results are transferred to REVIT on the basis of the results on grid points. In RFEM, the grid for the surfaces is set to 0.5 m by default. For the surfaces, enter a fine grid here and the graphical display of the results in RFEM and REVIT is comparable.

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First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

Wind Simulation & Wind Load Generation

With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated 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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