Robot Structural Analisys water pressure foundation slab and uplift?

[krabadavar]

Hello,

I am trying to model a office building with water pressure under.

I put springs under the foundation slab and the water is in a separate load case, but I get no moments from that load case. I have tried to model it as auxiliary but no effect.

...And further I will need to avoid the uplift, but it is saying  "No convergence .....", but I suppose I have to solve the problem with the linear load before this

I saw some possible solutions of this, but I can not understand why I am getting these zeros when I have only the foundation slab with springs.

I can not attach the model itself - I am getting the message bellow:

[Romanich]

Hi @krabadavar ,

zip the model first or share via any cloud service 

[Krzysztof_Wasik]

HI @krabadavar 

If you are using non linear analysis caused by uplift effect definition, do not calculate simple load cases. Set simple load cases as Auxiliary. Water pressure effect does not act separatelly. Regard combinations with at least dead loads combined with water pressure.

[krabadavar]

Thanks, here is the model

[Krzysztof_Wasik]

Hi @krabadavar 

With uniform (water) pressure applied to foundation, no other loads defined and only elastic foundation defined (as UZ support) for the same (loaded) foundation slabs I would not expect significant moments in the foundation.

Model is moved upward (almost uniform UZ translation for whole model) so there is no reason for foundation slab bending.

Check Dead load + water load combiantion (water will not act without dead load) for moment distribution. 

[krabadavar]

I did a manual combination with all the other loads and the water (just to see the results) and there are still these zeros, however in every other simple case there are values in the results .But you are right, the displacement are very big - the building is "flying" in that manual combination. The question is how to take these moment from the water into account. 

[Krzysztof_Wasik · Accepted solution]

Hi @krabadavar 

In your file there are Auxiliary cases which are used in combinations. When linear static is calculated auxiliary cases cannot be used in combinations (causes zero results ). Remove auxiliary definition from simple load cases when linear static is used. Then you will get non zero results for combinations.

[krabadavar]

Thanks a lot!

I will accept this as an solution, but because I never did successful calculation with an uplift, could you give me some advice to avoid "Non convergence ....". In that model I did not have an uplift, but if I remove several floors, just to see it works, it gives again  non-convergence problem.

And also if I define springs with an "Uplift" option, shall I have only manual combinations? Because it makes all the cases nonlinear, and then gives that error:

[Krzysztof_Wasik]

Hi @krabadavar 

Regarding non convergence of the model with uplift effect refer to

Non convergence for model with uplift effect defined

Regarding using automatic combinations in nonlinear model refer to

Lack of load cases message for nonlinear model