2192x

2020-08-18

Question

When using a line release, I get an error message saying that the model is unstable. Why?

Answer:

Image 01 shows a model where Surface 1 and Surface 2 should rest on Member 1 and Member 2. Member 1 and Member 2 should be supported by Nodal Supports 1 and 2.

FAQ

FAQ 004632 | When using a line release, I get an error message saying that ...

Structural System

For decoupling the members from the surfaces, a line release type shown in Image 02 is defined. The displacement u_z is only released in the case of a tensile force; the other displacements u_x, u_y and the rotation φ_x are always released.

Line Release Type

Line Release 1 is defined on Line 5 and releases Member 1 (Image 03).

Line Release 1

Line Release 2 is defined on Line 14 and releases Member 2 (Image 04).

Line Release 2

Member 1 is now defined on Line 15, generated by the line release with Node 12 and Node 13, and Member 2 is defined on Line 16, generated by the line release with Node 14 and Node 15 (Image 05). Members 1 and 2 have different nodes (13 and 14) at their intersection and are not connected to them.

Lines and Nodes of Members 1 and 2

Furthermore, Nodal Supports 1 and 2 are defined at Node 5 and Node 10 and thus support the surfaces, but not the members (Image 06).

Nodal Supports

During the calculation, the instability message shown in Image 07 is displayed because the members are unsupported.

Error Message "Stiffness Matrix is Singular"

The connection of Member 1 and Member 2 can be created by defining Node 13 generated by Line Release 1 as a definition node in Line Release 2 (Image 08). Members 1 and 2 then share the same Node 13 and are connected to it.

Line Release 2 with Definition Node

Furthermore, you have to define Nodal Supports 1 and 2 at the nodes of Members 1 and 2 (Image 09).

Nodal Support on Members 1 and 2

Author

Ms. von Bloh provides technical support for our customers and is responsible for the development of the SHAPE‑THIN program as well as steel and aluminum structures.

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2024-05-15

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RFEM 6 | Students | Introduction to Steel Design

2024-05-16

Consideration of Construction Stages in RFEM 6

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Consideration of Construction Stages in RFEM 6

2024-05-23

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$Steel Structures in RFEM 6 \n Part 1: Modeling, Load Input$

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$Steel Structures in RFEM 6 \n Part 2: Combinations, Design, Documentation$

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2024-10-16

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2024-11-13

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Videos

FAQ

FAQ 004632 | When using a line release, I get an error message saying that ...

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Knowledge Base Articles

KB 001879 | Influence of Bending Stiffness of Cables

This article describes and explains the influence of bending stiffness of cables on their internal forces. Furthermore, the text provides information on how this influence can be reduced.

KB 001848 | Timber Column Design as per the 2018 NDS Standard in RFEM 6

Using the Timber Design add-on, timber column design is possible according to the 2018 NDS standard ASD method. Accurately calculating timber member compressive capacity and adjustment factors is important for safety considerations and design. The following article will verify the maximum critical buckling strength calculated by the Timber Design add-on using step-by-step analytical equations as per the NDS 2018 standard including the compressive adjustment factors, adjusted compressive design value, and final design ratio.

RWIND 2 is a program for generating wind loads based on CFD (Computational Fluid Dynamics). The wind flow numerical simulation is generated around any building, including irregular or unique geometry types, to determine the wind loads on surfaces and members. RWIND 2 can be integrated with RFEM/RSTAB for the structural analysis and design or as a stand-alone application.

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Lines and Nodes of Members 1 and 2

Nodal Supports

Error Message "Stiffness Matrix is Singular"

Line Release 2 with Definition Node

Nodal Support on Members 1 and 2

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Display extended strains of members, surfaces, and solids (for example, the important principal strains, equivalent total strains, and so on) in the Project Navigator - Results in RFEM as well as in Table 4.0.

For example, you can display governing plastic strains when performing the plastic design of connections with surface elements.

Export RFEM or RSTAB Models to *.glb or *.glTF Format

RFEM and RSTAB models can be saved as 3D glTF models (*.glb and *.glTF formats). View the models in 3D in detail with a 3D viewer from Google or Babylon. Take your VR glasses, such as Oculus, to "walk" through the structure.

You can integrate the 3D glTF models into your own websites using JavaScript according to these instructions (as on the Dlubal website Models to Download).

Frequently Asked Questions (FAQ)

Can I display node coordinates in my model?

Can I use SHAPE-THIN 9 in combination with RSTAB 8?

Has the RF-TOWER add-on module for RFEM 5 already been added to RFEM 6?

Where can I find my customer number in RFEM or RSTAB?

Is it possible to define member nonlinearities for beam members?
For example, can I define a member that absorbs all internal forces, except for the compressive axial forces?

How can I exchange data between RFEM 5 / RSTAB 8 and Tekla Structures 2023?

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