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• ### For a tapered member, I get the error message "Invalid (incompatible) arrangement ...". What can I do?

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A taper describes a member or a surface with a variable cross-section. The cross-section type must be consistent, for example, I-shaped cross-sections at both member ends.

In our example, we have a member with a PRO cross-section and a QRO cross-section.

To create a tapered member here, you should use a parametric cross-section for the member start and end:

This allows you to calculate the tapered member.

• ### Does the program use different values of modulus of elasticity for different temperatures? How to activate it?

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Temperature-dependent stress-strain properties of an elastic isotropic material can be defined in a diagram or imported from [Excel]. These properties are considered for member and surface elements subjected to thermal load (changes or differences in temperature).

The Reference temperature defines stiffnesses for the members or surfaces that have no temperature loads. For example, if a reference temperature of 300 °C is set, the reduced elastic modulus of this point of the temperature curve is applied to all members and surfaces.

The Options dialog section allows you to control if the Poisson's ratios that are applied to the complete temperature diagram are identical. Clear the check box to access the Poisson's Ratio table column for individual entries.

You have to select and define the Temperature/Modulus diagram by your own.

• ### I would like to move some elements. When moving, my members are deleted, what is the reason?

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You have probably created nodes that were automatically generated by the program and thus locked.

You can unlock these nodes by selecting the nodes and then editing them. There you will find the option to unlock the nodes.

• ### A rigid member should only be able to absorb tensile forces or only compressive forces. What are the options for considering these nonlinearities in the calculation?

There are two options for defining the failure:

1. Assignment of member nonlinearity
For the member types "Beam" and "Rigid", you can define a member nonlinearity for each member. You can find the corresponding option in the "Settings" tab (see Figure 01).

2. Assignment of nonlinear member hinges
Alternatively, you can define a member end hinge with failure criterion for the member. For the desired degree of freedom, you can assign the hinge condition with nonlinearity accordingly (see Figure 02).
• ### I want to support a member along its line. When defining a fixed line support on the line of the member, the check leads to an error message regarding the undefined surface. How can I fix the problem?

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Line supports are only intended for the lines that belong to a surface. For the support of members along their line, it is necessary to define member foundations (also applies to RSTAB), see the figure.

• ### How can I consider a hole in the web that is only near the support? The parameterization can only be applied to the centrally arranged holes with the same distance.

In this case, the following options are available:

1) Corresponding division of the beam (right-click Member → Divide Member) and set the parameterization in the way that there is only one central hole for one of the beams, see Figure 01.

2) Generating surfaces from the member (right-click Member → Generate Surfaces from Member), inserting a circular opening, defining a result beam, see Figure 02.

• ### Is a load considered within the surface for "Nodal support with column"?

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The load within this area is not taken into account, which can be clearly seen in the example in Figure 01. Here, a homogeneous temperature load (Tc only) was applied, which leads to stress peaks, although the surface can freely strain.

If it is important to consider the load, you can also model the support manually. To do this, simply create an opening of the size of the column and create a new surface corresponding to the surrounding surface (see Figure 02). The values for the spring stiffnesses can be found in the dialog box (see Figure 03).

A surface loaded in this way is then also without stress in the case of a temperature load, as shown in Figure 04.

• ### After opening a duopitch roof beam from RX‑TIMBER in RFEM/RSTAB, it is displayed with a gap in the apex zone. Does this affect the calculation?

The cross-sections of members are always related to the centroidal axis in RFEM/RSTAB. The rendering is adjusted accordingly. This has no influence on the calculation.

• ### How can I transfer the effective lengths of members by using the COM interface?

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The factors for the effective lengths are transferred by using the interface for the member (IMember), which is called SetEffectiveLengths(). Use GetEffectiveLengths() to read out the data:

// get interface to running RFEM application.iApp = Marshal.GetActiveObject("RFEM5.Application") as IApplication;iApp.LockLicense();// get interface to active RFEM model.iModel = iApp.GetActiveModel();// get interface to model data.IModelData2 iModData = iModel.GetModelData() as IModelData2;// get interface to member 1IMember iMem = iModData.GetMember(1, ItemAt.AtNo);MemberEffectiveLengths memEffLen = iMem.GetEffectiveLengths();memEffLen.No = 1;memEffLen.CheckBucklingLoad = true;memEffLen.Enabled = true;memEffLen.FactorU = 1.1;memEffLen.FactorV = 1.2;memEffLen.FactorY = 1.3;memEffLen.FactorZ = 1.4;// set new effective lengths dataiModData.PrepareModification();iMem.SetEffectiveLengths(memEffLen);iModData.FinishModification();

Please note that it is only possible to read out the properties for the effective lengths (for example, EffectiveLengthY) of the MemberEffectiveLengths structure and the CriticalBucklingLoad property.

• ### How can I additionally model welds for the connection of two surfaces with a contact solid?

Since the boundary surfaces of contact solids can only be of the Null Surface type, it is necessary to model additional surfaces with a section. The following is an example for this.

There is a reinforcement of a plate with an additional plate. Both plates are connected by means of a contact solid:

In order to simulate a weld, borders are required on both plates:

You can simply create the bottom border by inserting a new rectangular surface. In this case, the program asks whether the surface should be integrated into the base surface, which must be confirmed by clicking Yes. There are then two openings in the bottom surface; one in the outermost surface where lies the surface for the border, and another in the surface for the border where lies the bottom surface of the contact solid:

For the upper border, it is also necessary to create a new surface, and the opening to the upper surface of the contact solid must be inserted manually:

After creating the borders, you can insert the actual surfaces for the weld:

If the reinforcing plate is subjected to tension now, the modeled weld transfers the tension stresses:

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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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