Steel Design - Bug?

[RRufino]

Hello, i´m writing to discuss with you what is happening at one steel structure model.

After label all columns and join them at the same group (3-Pilares) i went to code group design where robot tells me that for this group and with HEA section i`m being conditionated by bar 44. Clicking at the result and changing at the box below "Auto" my section to HEA 220 i can see which result i had to this bar with this section.

As i wasn´t believing in that results i verified just bar 44 (with HEA220 on the model) at Member verification where it shows a very different result for the same point and same load case.

Already strange is the fact that when i go to code group verification and check group 3 the bar that is condionating results is not 44 anymore.

Can you help me to understand this.

Model and printed results in attachment.

[Artur.Kosakowski · Accepted solution]

If you look at the results of the group design you can see that what governs them is the exceeded slenderness limit rather than capacity of the particular section. You can see that when you run verification for all the bars that belong to this group the slenderness calculated for bar 39 is excessive. When you run group design Robot tries to find the section that is sufficient (ratio and slenderness limit)  for all columns that belong to the group and in this case due to slenderness issue is not able to. As you defined the buckling length as being dependent on the stiffness of the top and bottom nodes of the column the increase of the stiffness of the column itself (larger section) and keeping the original section of the beams causes the slenderness to increase. In the current version of Robot for the buckling definition with adjoining bars when you replace the section found by the group design with another and then you press Auto some of the intermediate results calculated for the section you manually replaced are still used . This is what causes the difference in results comparing with the verification of the single bar with the same section  as manually selected.

The group verification result shows the bar with the highest ratio. Try to run verification of all bars that belong to the group 3 and sort the results by ratio.

Thank you for sending this example. We will investigate it further to see if some improvements in the procedures that are currently used could be done in the future.

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.

[RRufino]

Artur, thanks by the prompt response.

Now i already understood what is happening but i cannot agree that group verification just take in account ratio and not slenderness. I could swear that in previous versions, Robot took in account both, ratio and slenderness, at group verification.
How much dangerous could be if you just watch group verification results? I think quite enough to change this, i believe that many engineers don't know this.

Thanks a lot.

[Artur.Kosakowski]

The check for slenderness limit during verification of groups (in addition to ratio) is available after installing SP1 for Robot 2012.

[RRufino]

I'm glad to hear that.

Thanks.