raft foundation

[lis2984]

Good morning

I m learning Robot 2011.

I m trying to model a raft foundation

would you please give me the steps?

[Rafal.Gaweda · Accepted solution]

ordinary plate but in thickness defintion add soil elasticity

[lis2984]

thxs!

[willjvizcaya]

Hi, im also new with the slab foundation and elastic ground..

I have made this model for a slab foundation, i hate a ellastic coefficient of 25Ton/m3 but i dont think i defined correctly the planar Kz since soil pressure in the result maps goes above 180 T/m2 ( According to soil study Max 25Ton/m2).

1) Can you pls tell me how to correctly define Kz (it ask for a load above foundation) and Kz=0 when i do it this way.

2) is it ok to define a kz manually since i have the value.

3)How can i see the soil pressure correctly, the moment and shear diagrams?? i have seen it in other models but cant find the panel cut tool.

Thank you for ur help.

Regards

[Rafal.Gaweda]

Hi, im also new with the slab foundation and elastic ground..

I have made this model for a slab foundation, i hate a ellastic coefficient of 25Ton/m3 but i dont think i defined correctly the planar Kz since soil pressure in the result maps goes above 180 T/m2 ( According to soil study Max 25Ton/m2).

1) Can you pls tell me how to correctly define Kz (it ask for a load above foundation) and Kz=0 when i do it this way.

I do not understand your model data. If you know kz = 25 T/m3 so why have you specified kz~3000 T/m3 ?

Take a look below sw of your slab is 1680 T and it gives pressure 34,46 T/m2 ; soil kz = 25 T/m3 means that if you have load of 25 T/m2 it will be displaced 1m. So in your case you get 1,34m displacement.

2) is it ok to define a kz manually since i have the value.

Yes

3)How can i see the soil pressure correctly, the moment and shear diagrams?? i have seen it in other models but cant find the panel cut tool.

Results menu \ Panel Cuts

[webcy]

It's necessary to assign supports? Or I need to delete the supports of walls and columns? Or maybe It's necessary to assign planar support for the plate? Can you help me Rafael? Thank you.

[Artur.Kosakowski]

Hi @webcy

For a raft foundation walls and columns act as objects to transfer load from the above part of a building rather than supports. The best is to define supports is to add elastic soil in the definition of the panel (raft foundation) thickness. Mind that in addition to KZ you also need some horizontal restrains (e.g. UZx and UY supports or KX and KZ in the definition of the elastic soil) to avoid instabilities.

I hope this helps.

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.

[webcy]

Thank you Arthur, one more question, how can I add some horizontal restrains (e.g. UZx and UY supports or KX and KZ in the definition of the elastic soil) to avoid instabilities? Can you help me with a screenshot of your suggested configuration please? Thank you!

[Artur.Kosakowski]

Hi @webcy

See the slide from the 16th Robot webinar on instabilities

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.

[mustafahesenow]

Hi @webcy

Fallow the picture

[webcy]

Very helpful Mustafa! So, if my KZ is for example KZ=700 KN/m3, I need to assign for Ky and Kx the value of Ky= 70 KN/m3 & Kx=70 KN/m3??? This could have an impact on calculations? 

Can you help me with another topic? I need foundation with eccentricity (foundation around a site near to other buildings) do you have any suggestion or a shortcut to avoid problems?

Thank you!

[mustafahesenow]

Hi @webcy

Very helpful Mustafa! So, if my KZ is for example KZ=700 KN/m3, I need to assign for Ky and Kx the value of Ky= 70 KN/m3 & Kx=70 KN/m3??? This could have an impact on calculations? 

yes correct there wont be  any impact on the calculation .

[webcy]

Can you help me with another topic? I need foundation with eccentricity (foundation around a site near to other buildings) do you have any suggestion or a shortcut to avoid problems?

Thanks!

[mustafahesenow]

Hi @webcy

Its my pleasure to help you my friend .

Please write it as new topic to avoid mixing between the topics and to make easy to find for  our friends when they will look at similar case.

[webcy]

Thank you Mustafa!

This is the link for the new post.

https://forums.autodesk.com/t5/robot-structural-analysis-forum/foundations-with-eccentricity-neighbo...

[fredkishawi12]

Nice topic. So if I choose to follow your first suggestion and apply my Kx and Ky in the tangent elasticity field I get a warning no supports defined. So its ok to ignore this warning @Artur.Kosakowski?

[Artur.Kosakowski]

Hi @fredkishawi12

So if I choose to follow your first suggestion and apply my Kx and Ky in the tangent elasticity field I get a warning no supports defined. So its ok to ignore this warning @Artur.Kosakowski?

Yes, it can be ignored.

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.

[hashimkhalil4]

what about Ux and Uy 

?

[me1205377]

as Mr. mustafa said you can assume Ux , Uy  to be 10% of your Kz value

[hashimkhalil4]

he talked about Ky and Kx i think .  not Ux&Uy ? 

@me1205377