Design of thin walled C section

[Anonymous]

Hello all

I have made 2 different thin walled sections of the same geometry but different gauges in robot. I have gone through the procedure of calculating all the section properties and then adding the section to the thin walled database and manually adding all the section proerties to it. 

I have then created the design paramters and checked thin walled section design.

The strange thing now is when the two sections are used the thicker section of the two comes out as a higher utlistation. (I have used one section with 2mm and one with 2.5mm thickness).

Looking into the calculations it seems that for the thinner section it does not calculate the effect elastic modulus (Weff,y; Weff,z) but does so for the thicker section which therefore leads to reduced section properties below that of the 2mm thickness.

Would there be a reason for this in the programs calculations? I cant undertand why there would be no calculation for reduced section properties of the thinner 2mm section. They are both set to the same deisgn parameters, experience the same forces and the section properties for both sections are correct.

Thank you for your time.

Oscar 

[Artur.Kosakowski]

Hi Oscar,

Have you followed one of these two ways of creating a thin wall section?

http://knowledge.autodesk.com/support/robot-structural-analysis-products/troubleshooting/caas/sfdcar...

http://knowledge.autodesk.com/support/robot-structural-analysis-products/troubleshooting/caas/sfdcar...

[Anonymous]

Hi Arthur

Yes I have followed what was done in the first link. I have done this quite alot and haven't come across this before. 

Thanks for the quick reply!

Oscar 

[Artur.Kosakowski]

Could you attach the both rtd file and your user section database and indicate on a screen capture what to look at please?

[Anonymous]

attached is the model file

[Anonymous]

attached below is the section databse

[Anonymous]

below are the images attached

Sorry for doing this in 3 seperate posts I have only just realised you can add more than one attachmemnt!

Thanks again

[Artur.Kosakowski · Accepted solution]

The 2.5 mm section has got the ends of C shape defined as 11 mm straight parts. Robot during the thin wall section verification checks its geometrical 'correctness' too. In case of such short reinforcement of the flange the c/b ratio is calculated to determine if it has got sufficient stiffness to be recognized as such. The check is done according to the paragraph (5.2.(2) of EN 1993-1-3 (formula 5.2a):

For the above mentioned section c/b = 11/65 = 0.169 < 0.2 therefore this vertical part is not considered as the reinforcement for the flange of the C shape meaning the flange is of class 4 becoming a cantilever rather than being supported at both ends.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Thank you Artur! You are a genius I would have never found that!

[ga137]

Is it possible to add a Double Channel section by the second method mentioned, as a thin member, and then perform cold formed steel design? I am having issues in the cold form design of some complex shapes such as double sigma section etc.