Robot Model Calculations Non-Converging When a Raft Slab is Input

[danielhagan]

Hi There,

I have been working on a model of a timber structure within Robot 2024. the model has been primarily used to find the design actions on the structure, however now I am looking to input a raft slab so that the actions within that can also be included from the Robot model.

The model has been converted from a 3D Frame to a Building Design Structure Type so that the Slab can be input. When running the model without the slab and with pinned supports, there are no errors. However, with the slab input and the supports removed the wind combinations begin to non-converge. My team believe this is likely due to uplift, but note that this should not be an issue as the uplift from the 3D Frame indicates values that should be well exceeded by the additional weight of the slab.

Currently, the solution we have found is to have a 2000mm deep slab (this means the combinations do converge), however this is not practicable. Therefore, I wonder if anyone would be able to help by potentially identifying what is causing the non-converging cases?

Model attached in Zip Folder.

Many thanks for any help!

Dan.

[Simau · Accepted solution]

Hi @danielhagan 

Dont use TH30_CONCR for the raft,. Create a new FE Thickness with foundation elasticity as in the example below:

You have to many releases in your model. Without releases, the model converges (Model attached).

Starting with this model, add releseases by step and check if there is convergence, etc...

[danielhagan]

Hi @Simau ,

Many thanks for the quick reply!

I have used the model you provided in your reply to re-add the releases step by step. The model is now demonstrating results as we would expect with the slab input.

I have attached the model with the working releases (I have amended the ground slab slightly to suit our ground conditions), if you are interested.

Do you have any thoughts as to why the previous model did not work? It was previously working with base supports to the columns, but adding the slab caused the errors. Is it recommended to always redo all releases when adding ground slabs? The first screen shot is of the original working model, the second of the new model with the slab. It seems like there are more releases.

Thanks again for your support!

Kind Regards,

Dan

[Simau]

@danielhagan 

Do you have any thoughts as to why the previous model did not work? It was previously working with base supports to the columns, but adding the slab caused the errors

The previous model with supports didn't work also as there were instabilities Type 2 and non convergences.

Is it recommended to always redo all releases when adding ground slabs?

Not necessarily, instabilities appear whatever the type of foundation (supports, rafts)

In your new model you forgot to add uplift Uz+ in foundation parameters, not a problem in your case as there in no uplift in combinations results.

[danielhagan]

Thanks for spotting that, will amend to correct.

Thank you for the help!