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The Steel Design module in FEM-Design takes new leaps with the function Plastic Hinges

The Steel Design module in FEM-Design takes new leaps with the function Plastic Hinges

The release of FEM-Design 21 is just around the corner and a big new feature when it comes to the steel module is Plastic Hinges. With this tool, a plastic distribution of the stress across the cross section can be obtained and plastic mechanisms in the structure appear. This will also potentially affect the load distribution and provide a more realistic behavior.


This type of calculation uses a more advanced stiffness matrix for the Timoshenko beam theory, which includes a coupling part between the curvature and the axial strain. Due to this, a more nuanced behavior can be obtained, for single symmetrical profiles for example. If plasticity occurs in the cross section, the neutral axis can potentially move and consequently an axial load can cause curvature of the beam.

How does this function work practically in the program? Start by choosing whether or not you want to take plasticity into account. This is done under the "General" tab at object level. Here the user can choose whether they want to take plasticity into account in any specific load combination. Then the analysis is run with the "PL" setting selected under the settings for the load combinations (Setup by load combinations). An iterative process is now performed in which a plastic distribution of the stress across the cross section is allowed.

If the force cannot be redistributed to other parts of the structure, the calculation will stop and present the result of the last converged load step. FEM-Design also shows the first unstable position. With the help of these results, the designer gets a very good understanding of the mechanism and how it can potentially be avoided.

Under "Detailed results" for the stresses in the beam, we can see how the plastic distribution looks across the cross section.

The program uses an idealized elasto-plastic material model where the limit for plasticity is set to fy (e.g. fy = 355 for S355). Due to this, a smaller elastic part is obtained in the profile as the curvature is not infinite. This can also be seen in the picture above in the middle of the profile where the tension in the cross section is less than 355 MPa.


FEM-Design 21 is expected to be released at the end of January 2022 and it is the version with the most new features that we have released so far! Do not miss all the news that will be rolled out in the near future and feel free to take the opportunity to book a demo of the new version in your office. Just get in touch with one of our customer coaches and we will be happy to help you with this!


Sincerely
StruSoft team

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