Support definition for elastic ground

[Μηχανικος]

Quick question about support definition for foundations on elastic ground.

1. I want to design the foundation beams of a one-storey RC house.

2. The superstructure was designed using fully fixed supports at column base.

3. Foundation beams will be designed using winkler springs (modified supports) at column bases

      The support definitions are:

       UX - fixed
       UY - fixed
       UZ - spring with stiffness - RELEASED
       RX - spring with stiffness - RELEASED
       RY - spring with stiffness - RELEASED
       RX - fixed

4. I used the ks calculator as shown in the picture, but i only get the one value of UZ   KZ = 65876.60kN/m

My question now is: do i also need to calculate the HX and HY values for the rotation stiffness or Robot will use the value from KZ stiffness to automatically determine the HX and HY stiffnesses?

[HoshangMustafa]

Hello

Please find the attached link:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/hx-rx-elastic-ground-reaction/m-p/485...

[Artur.Kosakowski]

Hi @Μηχανικος

Has the topic indicated by @HoshangMustafa (thank you for your help) answered your question?

[Μηχανικος]

Actually no, i am still trying to understand but before i move on i would like to make sure that the

1) Elastic foundation coefficients are calculated correctly in the Building Soils - calculations coefficients. 

2) The supports assigned at column bases are correct

3) The elastic ground assigned on the foundation beams is also correct.

This is what i did:

1) The columns of the initial model were designed using fully fixed supports at column bases.

2) Now i need to design the foundation beams therefore the supports of the model need to be changed

     1) first i removed the fully fixed supports at column bases and replaced them with winkler springs as shown below

3) i then defined elastic ground properties for the foundation beams as shown below and assigned them to all foundation beams

The fact that i used winkler springs at column bases in addition to elastic ground conditions along all foundation beams, is this correct? is this the correct way when trying to calculate the forces transferred from Columns to foundation beams?

[Artur.Kosakowski]

Hi @Μηχανικος

You shouldn't define both nodal supports and elastic supports under the bars as you 'add them up" however I don't understand your approach. IMHO if you already designed the 'upper' part of the structure then what you may consider is to define only the continuous footings (in a separate model) with loads being the reactions from the fixed support one. Mind that you would need to add rotational stiffness to the elastic ground under the beams when you have torsional moments.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Μηχανικος]

I have used nodal supports to replace the fully fixed supports at each column base.

I did not use nodal supports below the foundation beams.

I only used elastic ground condition below the foundation beams.

Is this wrong? shall i delete all supports at column bases and define only elastic ground condition below the foundation beams?

[Artur.Kosakowski]

Hi @Μηχανικος

If your columns are sitting on the foundations beams IMHO you should delete nodal support from their bottom nodes as they would sort of duplicate boundary conditions as the beams are defined till the column nodes anyway. If you have actual isolated foundations under the columns which are ten connected 'together' by the foundation beams you may want keep them both.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Μηχανικος]

Ok, i have deleted the supports at the base of the columns since the columns sit on the foundation beams.

Now i need help in order to define the parameters for the "Building soils - calculations of K coefficients" specifically dimensions A & B. and foundation type

lets say i have a foundation beam connecting two columns with cross section dimensions, height = 45cm and width = 50cm, which is A and which is B (shown in the picture attached)?

And which foundation type shall i choose for the foundation beam? I assume the strip footing, indicated with letter b??

[HoshangMustafa]

A and B doesn't relate with height of beam.

[Artur.Kosakowski]

Hi @Μηχανικος

A and B stand for a ground beam length and width.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.