Dear Sir,
I have experience in Ram Element (RE) for a couple of years and I have found incorrected analysis results several times.
I'm not sure that they were software's bugs or I was wrong.
Mostly, I use RE for analysis and design steel portal frame using simplified 2D analysis.
Only in-plane loads are assigned, but the result shows out-of plane bending moment that shall not occur.
Moreover, the moment diagram does not equal to zero at hinge support.
I attached Ram Element file and summary pictures shown the problems above as link below
https://www.dropbox.com/sh/08of7gs8k2nlfbv/AADIfHvJPdgQlPI4aiFXfDUma?dl=0
Please clarify and advise
Best Regards,
Thanaanan
Your model has a custom shape in it called F 2000508, try editing that section using the check box for "Laterally restrained for torsion". This forces the member forces to be in the local axes not the principal axis which might be triggering your symptom as the tapered members principal axis can change based on section depth.
The other thing to try is running it with no offsets or cardinal point changes to see if the rigid links are somehow causing it.
Dear Seth,
Firstly, thank you for your advices.
I try to investigate the symptom using a very simple model (see picture A). The result of Ram element are compared to STAAD Pro results.
The model is a wide flange with web-tapered column. No node offset, but the member is not aligned vertically, this is to make the exact column center of gravity alignment.
I try to vary the bottom end depth of column from 200mm to 400mm (The top end is fixed). The results shown that, the moment distribution shape obtained from STAAD Pro is the same for all range of the bottom end depth and no out-of-plane bending occur (See picture C). In contrast, the results yielded by Ram element is different. The result of 300mm and 400mm bottom end depths are the same as STAAD Pro, but the result of 200mm bottom end depth is strange. The moment distribution shape is different and out-of-plane bending occur (See picture B).
In my opinion, the problem may caused by Metrix stiffness or Transformation Matrix that the program (Ram Element) used for analysis.
I will inform you again If I know more.
Cheers,
Picture (A)
I
Picture (B)
Picture (C)
Did you try selecting the "Laterally restrained for torsion" option in the custom section definition? I still think that's the key to this behavior where the principle axis of the tapered section reverse as the section depth is reduced.
For more see: https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/23793/ram-elements---local-versus-principal-axis-in-unsymmetrical-shapes
If that's not it, can you use the file - save as zip feature and send the resulting .zip file for review?
Hi Seth,
Yes, I did. It's not change the result.
Please find the file in link below,
https://www.dropbox.com/s/cdfjqatpdidjgi9/For%20Review.zip?dl=0
Regards,
That's just the .etz file, it does not have the custom sections in it. The way to zip up the model with all the custom data is to use
The file is attached.
https://www.dropbox.com/s/1w6haym3ue59c3z/For%20Review_171017.zip?dl=0
If you have any additional information, please let me know.
Thanks, there is definitely something wrong. If the base of the section is increased just 1 cm to d0=21cm, then it works properly, but once it goes below that to 20cm or less the program is getting something reversed. I'll log the issue.
Defect 768763: Moments reported at hinge when member principle axis rotated