# Stability proof with eigenform

**URL:** <https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792>\
**Category:** Product Support\
**Tags:** addon-steel-design, rfem-6, feature-request, set-of-members\
**Created:** [September 1, 2025, 8:08am UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792 "2025-09-01T08:08:08Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Mikalea](https://community.dlubal.com/user_avatar/community.dlubal.com/mikalea/32/74_2.png) [@Mikalea](https://community.dlubal.com/u/Mikalea)\
**Post date:** [September 1, 2025, 8:08am UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792/1 "2025-09-01T08:08:08Z")

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Hi,

I am currently calculating a steel hall with RFEM 6. I perform the stability verifications of the beams using the general method. When checking the results, I noticed that the eigenmode does not match my system.

 ![Demo Frage 3 screenshot](https://community.dlubal.com/uploads/default/original/1X/1ceb09284c115500dd799094cdf6684e498d8a33.jpeg)

From my point of view, the beam should not shift laterally in the middle of the span, since it is supported by the purlin. Have I overlooked something or found a program error?

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**Author:** ![clemens.gutmann](https://community.dlubal.com/user_avatar/community.dlubal.com/clemens.gutmann/32/1585_2.png) [@clemens.gutmann](https://community.dlubal.com/u/clemens.gutmann)\
**Post date:** [September 1, 2025, 8:09am UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792/3 "2025-09-01T08:09:17Z")

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Hi Mikalea,

Thank you for your message!

To analyze the problem more precisely, the **model file** would be very helpful:

➡ Click on _File_ → _Save As_ and choose the following settings to reduce the file size:

 ![image](https://community.dlubal.com/uploads/default/original/1X/8b1a4d47ea10737b559f12b01985d0ad3b4a8096.png)

➡ Then upload the file here (e.g., \*.rf6, \*.rs9) – this way the community can also contribute to the solution.

🦉 Don’t want to share the file publicly? No problem – send it to me via direct message: click on my _profile picture_ or my _username_ → _Message_.

Best regards  
Clemens Gutmann

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**Author:** ![clemens.gutmann](https://community.dlubal.com/user_avatar/community.dlubal.com/clemens.gutmann/32/1585_2.png) [@clemens.gutmann](https://community.dlubal.com/u/clemens.gutmann)\
**Post date:** [September 1, 2025, 9:36am UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792/5 "2025-09-01T09:36:19Z")

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Hi Mikalea,

Thank you very much for the model file.

Your observation is correct, the beam shifts laterally in the middle of the field. This is because the laterally adjacent members are not entered as intermediate supports in the boundary conditions for the general method, which is why they are not considered in the stability design.

To change this, you need to check the box for intermediate nodes, and then you can add further intermediate supports using the button on the far left (see image below). If the intermediate supports have different properties, you also need to check the corresponding box (see image below).

RFEM 6 automatically recognizes the associated nodes along the member set, even if the boundary conditions are assigned to multiple member sets. It is important that the member sets are oriented the same way and have the same number of intermediate nodes so that the definition fits all member sets. To better control this, there is a button in the window on the right that allows you to switch to the model view. In this view, the boundary conditions are displayed as violet nodal supports, so you can easily check whether they are defined correctly (see image below).

 ![image](https://community.dlubal.com/uploads/default/original/1X/1ca995e56f9a6baf490530bed8335e5321afdb7d.jpeg)

If you have any further questions, just write. I’m happy to help you 😃

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**Author:** ![Mikalea](https://community.dlubal.com/user_avatar/community.dlubal.com/mikalea/32/74_2.png) [@Mikalea](https://community.dlubal.com/u/Mikalea)\
**Post date:** [September 1, 2025, 11:08am UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792/6 "2025-09-01T11:08:53Z")

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Hi Clemens, thanks for the tip. I tried it that way, but the intermediate support is not detected automatically. Wouldn't that be a useful feature?

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**Author:** ![clemens.gutmann](https://community.dlubal.com/user_avatar/community.dlubal.com/clemens.gutmann/32/1585_2.png) [@clemens.gutmann](https://community.dlubal.com/u/clemens.gutmann)\
**Post date:** [September 1, 2025, 12:36pm UTC](https://community.dlubal.com/t/stabilitatsnachweis-mit-eigenform/1792/7 "2025-09-01T12:36:44Z")

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Yes, that would definitely be a helpful feature. I have forwarded the idea to our development team (RUS ID 5071). 🚀

Thank you very much for the feedback and the suggestion!