Hello,
I'm having a problem with cross-section optimization in RFEM 6 using the Steel Design add-on.
As you can see in the screenshot, the utilization ratio was 0.768 before optimization. After running the optimization (optimize current row), the program selected a larger cross-section and the utilization dropped to 0.164.
This is the opposite of what I need — my goal is to reduce the weight of the section, not increase it. It seems odd that the optimization would move toward a heavier profile when there was still capacity available.
Interestingly, the optimization works as expected for I-sections. It's only with equal-leg L-sections that I get this behavior, and I can't figure out why.
Does anyone know what might cause this, or whether there's a setting I'm missing for angle sections?
Thanks in advance.
Hi waelnoman,
thanks for your message!
I tested this and was not able to recreate this issue.
To analyse 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:
Then upload the file here (e.g. *.rf6, *.rs9) – this way, the community can also contribute to the solution.
Prefer not to share the file publicly? No problem – send it to me via direct message: click on my profile picture or user name → Message.
Best regards
Matthias
Hello,
Thanks for your reply here look at the cross section number 3, before optimization the utilization is 0.884. try to do optimization, RFEM will choose heavier cross section not lighter.
Best regards,
tower.rf6 (1.6 MB)
Wael
Hello, this is just kindly reminder for this topic.
Thanks so much.
Best regards,
Wael
Hi waelnoaman,
The problem is that all members with cross-section 3 have assigned effective lengths. Since cross-section 3 is an unsymmetric cross-section, the equivalent member method for stability design cannot be applied. This leads to a utilization greater than 1.0.
The optimization process is then searching for a cross-section for which the utilization is smaller than 1.0, which can never be found. Therefore, the optimization sticks with the largest cross-section.
Just unassign the effective length for all members with cross-section 3. This should fix the issue.
Best regards
Matthias
Hi Mattias,
Thanks so much. but I have a question instead of the equivalent method for the stability verifications for the unsymmetric members, which method we can use?
Best regards,
Wael
