Error 2809 - Modal Analysis

[Gabriela.Bercot]

Hi,

I am working a model and I am getting error 2809, it seems to be something linked to the Modal analysis as when I delete this, there's no issue. However, I need this one the analysis. I checked everything I thought.

Could someone help me with this? Not sure how to fix it.

[Krzysztof_Wasik]

Hi Model is not supported. It causes static instability. For such model program cannot calculate normal modes.

[Gabriela.Bercot]

How could I have seismic loads in this condition? I quite don't understand, I produced a model before and had Modal Analysis/Seismic before and I haven't got the same error - something I may be missing perhaps

[Krzysztof_Wasik]

HI @Gabriela.Bercot 

In my opinion supports are missing

I have deleted all load cases except load self-weight and run calculation. Refer to displacement presentation.

You have to define supports in the model. Otherwise all results will be incorrect.

[Gabriela.Bercot]

Understood, I'll try that. I supposed to have a raft foundation, how do I define this on the model as the support?

[Krzysztof_Wasik]

Hi @Gabriela.Bercot 

I would recommend defining elastic support within slab 400 thk thickness label.

Refer to

 How to apply soil elasticity on a raft foundation created as a panel in Robot Structural Analysis

Definition procedure is presented also in the following video

[Gabriela.Bercot]

Hi @Krzysztof_Wasik, thanks for your response, I added the spring values to the raft slab. However, I am still getting weird values on my bending diagrams. Any idea why that could be happening?

[Krzysztof_Wasik]

HI @Gabriela.Bercot 

Which is member number with weird results. Could you explain what you expect. 

[Gabriela.Bercot]

Hi @Krzysztof_Wasik.

I was expecting diagrams looking like the picture below as I didn't set up releases for my beams - the picture it is just an indicative from another model.

However I am getting bending (My) diagrams like this, it seems something is off with the model

[Krzysztof_Wasik · Accepted solution]

Hi @Gabriela.Bercot 

Members 44 to 48 are connected to "wall" members. Moment shows interaction with wall finite elements.