# Frequently Asked Questions (FAQ)

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

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#### Answer

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.

• ### How can I create a user-defined coordinate system via the COM interface and then assign it to a nodal support?

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#### Answer

For the programming using the COM interface, a nodal support has the "ReferenceSystem" and "UserDefinedReferenceSystem" properties. "ReferenceSystem" allows you to define the type of the user-defined coordinate system (for example, "Rotated" or "Coordinate System"), and depending on which type has been selected, this type is then defined via "UserDefinedReferenceSystem."

In the following example, the "Coordinate system" was set as the type and a user-defined coordinate system was also created for it:

//  create user defined coordinate systemIGuideObjects iGuide = iModel.GetGuideObjects();//  delete cosy No 2UserCoordinateSystem[] csList = iGuide.GetCoordinateSystems();if (csList.Length > 1){    for (int i = 0; i < csList.Length; ++i)    {        if (csList[i].No == 2)        {            iGuide.PrepareModification();            iGuide.DeleteObjects(GuideObjectType.CoordinateSystemObject, "2");            iGuide.FinishModification();        }    }}//  define new cosy No 2UserCoordinateSystem uCs = new UserCoordinateSystem();uCs.Name = "test";uCs.Comment = "test";uCs.No = 2;uCs.IsValid = true;uCs.Origin.X = 1;uCs.Origin.Y = 0;uCs.Origin.Z = 1;uCs.Point1.X = 2;uCs.Point1.Y = 0;uCs.Point1.Z = 1;uCs.Point2.X = 1;uCs.Point2.Y = 1;uCs.Point2.Z = 2;//  set cosy No 2iGuide.PrepareModification();iGuide.SetCoordinateSystem(uCs);iGuide.FinishModification();//  create nodal support with user defined cosyNodalSupport ns = new NodalSupport();ns.SupportConstantX = -1;ns.SupportConstantY = -1;ns.SupportConstantZ = -1;ns.RestraintConstantX = -1;ns.RestraintConstantY = 0;ns.RestraintConstantZ = -1;ns.Comment = "user defined cosy";ns.NodeList = "1";ns.ReferenceSystem = ReferenceSystemType.UserDefinedSystemType;ns.UserDefinedReferenceSystem.ObjectNo = 2;ns.UserDefinedReferenceSystem.Type = UserDefinedAxisSystemType.DefinedCoordinateSystemType;iModData.PrepareModification();iModData.SetNodalSupport(ns);iModData.FinishModification();

To be able to create the coordinate system, the interface for the guide objects is required: 'IGuideObjects'. With the "DeleteObjects()" function, an existing coordinate system of Number 2 is first deleted and a new one is created with "SetCoordinateSystem()." Please note the "Prepare/Finish-Modification" block to be able to transfer the new element.

The nodal support is transferred via the "IModelData" interface. Again, the "Prepare/Finish-Modification" block is required.

• ### How can I define the orientation of nodal supports in my structure to a specific member axis?

#### Answer

To adjust a nodal support to a specific member axis, proceed as follows:

• Open the "Edit Nodal Support" dialog box → activate the "User-defined axis system" option.
• Click the "Edit User-Defined Axis System" button.
• Activate the "Same as member" option.
• Select members by using the corresponding button.
• Click OK to confirm.
• ### How can I determine the orientation of a nodal support perpendicularly to a line?

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#### Answer

Each nodal support has a local axis system X', Y', and Z'. By default, it is oriented parallel to the global axes X, Y, and Z. The "User-defined axis system" option, allows you to rotate the local axis system of the support (Figure 01).

If you want to align the nodal support perpendicularly to a line, you can use the "Same as line" option (Figure 02). The "Same as line" option is only available for straight lines. The local axis system of the support is aligned parallel to the local axis system of the line. The local axis system of the line can be displayed in the Project Navigator - Display using Model → Lines → Line Axis Systems x,y,z (Figure 03). The axis system of the line can be influenced by the line direction and line rotation. To change the line direction, right-click the line and select the "Reverse Line Orientation" option in the shortcut menu (Figure 04). The line rotation can be set in the "Rotation" tab of the "Edit Line" dialog box (Figure 05).

As an alternative, you can determine the orientation of the axis system of the nodal support by using a user-defined coordinate system or by specifying three nodes perpendicular to the line.

The three options are shown in the video. For the orientation of the support axis system using a user-defined coordinate system or the specification of three points, an auxiliary straight line is created perpendicular to the line. Thus, it is easily possible to align the axis perpendicular to the line.

• ### How can I rotate a nodal support?

#### Answer

A nodal support can be rotated as follows:

• Open the "Edit Nodal Support" dialog box, see Figure 01.

• In the "Support Axis System" section, select the "Ridig" option for "User-defined axis system."
• Click the "Edit User-Defined Axis System" button.
• In the "Edit User-Defined Axis System" dialog box, set the options for the support rotation as desired, see Figure 02.

• ### How can I use springs for nodal supports in the design of sets of members in RF‑/STEEL EC3?

#### Answer

To adjust nodal supports of sets of members, go to Window "1.7 Nodal Supports." There you can adjust the nodal supports for the set of members.

Left-click once next to the check box of the support condition that you want to adjust. A selection symbol appears where you can select the "Spring" type. Now, you can enter the spring properties.

• ### Some of my supports are rotated by 180 degrees. How can I rotate the view of a nodal support?

#### Answer

The discrepancy is probably caused by rounding differences of the nodes. Please adjust the X‑coordinates of the nodes accordingly.

The "Regenerate Model" feature could also be helpful, you can find it in Tools.
• ### I would like to define a line support with ineffective tension and apply the tension force on this line by using a nodal support instead. Why does the line support still receive a tension force?

#### Answer

If nodal supports are modeled on supported lines, this may lead to problems and incorrect definitions. Therefore, the following warning message appears in the plausibility check.

Internally, the line supports and nodal supports are treated on each FE node. If there is a nodal support located on a line support, an FE node thus receives several support definitions. If the defined directions of the supports are not equal, this is not critical and the warning message can be ignored. If the same directions are defined several times, discrepancies may occur.
In the case of a line support that is failing under the tension and a nodal support on this line, the tension force thus results in the FE node which, however, counts to the line support and to the nodal support.

To avoid this behavior, it is possible to insert a short line without a support definition in the area of each nodal support. It may also be useful to model a tension bracket by using a newly defined member. The force transmission can then be adjusted by using the support of the member, the member type itself, and the member end release.

In general, the support stiffenings should be estimated in a realistic way; in the example, rigid supports were assumed as a simplification.

• ### How can I deactivate or modify the individual nodal supports in the model by load case?

#### Answer

In RFEM 5 and RSTAB 8, there is the option to assign various stiffnesses to the individual objects, such as nodal supports, by load case. This feature can be found in the calculation parameters of the load cases and load combinations (see Figure 01).

In RFEM 5, the individual objects can also be deactivated by load case (see Figure 02).

The tab allows you to ignore certain objects of the model in the calculation. In this way, the effect of temporary members (construction supports) or supports can be analyzed, for example.
• ### I have created a 2D frame and would like to assign a lateral and torsional restraint to the ridge. Do I have to enter an intermediate lateral restraint or a nodal support in RF‑/STEEL EC3?

#### Answer

You can either define a nodal support or an intermediate lateral restraint in RF‑/STEEL EC3.

If there are already nodes in your actual RFEM or RSTAB model, we recommend you to directly enter a nodal support in Window 1.7 as in this case, you can select the nodes directly in the model See Figure 01.

If you want to consider intermediate support at a point in the beam where there is no node available in your structure, you can use an intermediate lateral restraint and specify the restraint type (for example, lateral and torsional restraint). See Figure 02.

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