topic Re: Section check not analized despite getting forces?? in Robot Structural Analysis Forum

Section check not analized despite getting forces??

Anonymous — Thu, 12 Feb 2015 11:59:27 GMT

Hello,

I don't understand why robot doesn't analize the members. I get some warnings of instablities but robot runs the calculations. The moments diagrams and deformations are the expected ones.

I'm trying to simulate a 2span beam supported in shorts arms. Like a facade purlins.

Purlins are user section database of less than 3mm. (I Already know the program doesn't run a thin walled section check for users sections. But I just want to check as a normal section in elastic field (class 3).

Whats going on?

Thanks

Re: Section check not analized despite getting forces??

Artur.Kosakowski — Thu, 12 Feb 2015 12:30:04 GMT

Ay and Az being 0s when you have shear forces. Try to save this section in the user section database with C shape type or edit these areas entering some values.

BTW: if you ryun manual check for axial force and bending (shears as )s you will get the results).

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.

Re: Section check not analized despite getting forces??

Anonymous — Thu, 12 Feb 2015 15:39:25 GMT

Hello,
I am aware that Ay and Az are 0. But I believe that is not the issue.

Try to delete all the releases and you will find out that then robot makes the checks (also without shear áreas).

Re: Section check not analized despite getting forces??

Artur.Kosakowski — Fri, 13 Feb 2015 10:16:30 GMT

The difference is not the lack of releases but the presence of axial force. IMHO the check of section defined in this way (without assigned section type and some parameters missing e.g. thickness of web, flanges etc.) could only be done for pure tension (axial force) as FX/AX compared to resistance.

You may consider one of these two solutions:

- save this section in the user database in one of the ways described below:

http://knowledge.autodesk.com/support/robot-structural-analysis-products/troubleshooting/caas/sfdcarticles/sfdcarticles/ROBOT-STEEL-DESIGN-how-design-user-defined-thin-walled-section.html

http://knowledge.autodesk.com/support/robot-structural-analysis-products/troubleshooting/caas/sfdcarticles/sfdcarticles/Robot-Steel-Design-How-to-code-check-a-member-of-Z-or-Sigma-shaped-thin-wall-section-according-part-3-of-code-NF-EN-1993-1.html

- define section by properties and assign it the type using these dialogs

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.

Re: Section check not analized despite getting forces??

Anonymous — Fri, 13 Feb 2015 12:23:43 GMT

Hi,
Definitely the axial load plays a role here. (please have a look to the attached example).

When an axial load is applied, robot makes the verification, when there is no axial load don't. (with the same section as before, without shear áreas and other section properties).

It doesn't make sense to me.

Re: Section check not analized despite getting forces??

Artur.Kosakowski — Fri, 13 Feb 2015 14:09:04 GMT

That's what I tried to explain

My point is that for section which is defined "incorrectly" in a sense that it hasn't got all the parameters required by the Steel design module the verification may be done incorrectly (e.g. C shape verified with formulas that are not intended for C shape) and the only "reasonable" check is for pure tension. The recommend workflow is to define a section in a way it is expected by the steel design module.

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.

Re: Section check not analized despite getting forces??

Anonymous — Fri, 13 Feb 2015 14:34:24 GMT

Hello,

I've just realised that the gamma of the bar is involved in this issue.

From the attached file, I reach the conclusion that: robot doesn't perform the member check when the bar has bending moment in z axis (weak) and there is no axial load.

To me totally non sense.

Re: Section check not analized despite getting forces??

Artur.Kosakowski — Fri, 13 Feb 2015 14:41:21 GMT

Please attach your user section database with this profile.

Re: Section check not analized despite getting forces??

Anonymous — Mon, 16 Feb 2015 16:48:12 GMT

Hello,
I sent you the database privately.
Thanks

Re: Section check not analized despite getting forces??

Artur.Kosakowski — Tue, 17 Feb 2015 10:20:28 GMT

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.