## Robot Structural Analysis

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# HELP with generating mesh for Rigid Diaphragm!!!

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Hello all, as the topic says, i have modeled a 4 storey RC building with raft foundation , the building has two core (shear ) wall and is being designed so that the shear wall can resist all the lateral load and the columns will resist gravity load, the problem is that when i define the mesh and generate it for the building only the panels assigned as shell gets generated i.e ( raft and shear walls ) but the other floor slabs assigned as rigid diaphragm dont get generated. see attached pdf file for the pic.

also i tried to define a new rigid slab with mesh element turned on and i assigned that to the floor slabs , the mesh gets generated but it gives me results of zero moment in all direction ( x &Y ) so i dont really know what im doing wrong , i tried the felixble diaphragm , it works but it gives less value of moment for core walls and the columns in that case have moments due to resisting some of the lateral load.

also attached is moment diagram of the core wall , should the moment diagram be combined togther like that for both core wall 1 and 2 ?? shouldn't they be separate diagram?? please help and thanks in advance for your answer.

NOTE : this model and the values i used for loads are just for educational purpose so dont mind the value of loads.

# Re: HELP with generating mesh for Rigid Diaphragm!!!

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, the problem is that when i define the mesh and generate it for the building only the panels assigned as shell gets generated i.e ( raft and shear walls ) but the other floor slabs assigned as rigid diaphragm dont get generated. see attached pdf file for the pic

The rigid diaphragm panel calculation model relays on rigid links rather than mesh generation

also i tried to define a new rigid slab with mesh element turned on and i assigned that to the floor slabs , the mesh gets generated but it gives me results of zero moment in all direction ( x &Y ) so i dont really know what im doing wrong

Try to replace full stiffening with with XY only as shown below:

also attached is moment diagram of the core wall , should the moment diagram be combined togther like that for both core wall 1 and 2 ?? shouldn't they be separate diagram??

I don't understand this point. Could you give some detailed description?

**Artur Kosakowski**

# Re: HELP with generating mesh for Rigid Diaphragm!!!

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thank you very much for the quick reply but i have some comments :

1 - you said in the first pic you embeded that rigid Diaphrgm rely on rigid links rather than on finit elements which is what i noticed when i was defining the calculation model for the panel so if it relies on rigid links how can i get the value of My and Mx in the panel using rigid links method ?

2 - if i would follow you second sugession which is to use stiffness in XY plane which is similar to flexible diaphragm i will get lower results for My in the core wall ( almost half the value if i would use rigid diaphragm ) and i wanted to get the worst case for designing the core wall.

so is it possible to have a full rigid diaphragm to be able to get the worst case for core wall and in the same time get results of My and Mx for the rigid floor??

3 - regarding the core wall question i was asking if that diagram for the moment of the core wall looks correct ? this is the first time i use robot to design core wall so i was thinking may be it will show each core wall seperate as a cantilever bar .

# Re: HELP with generating mesh for Rigid Diaphragm!!!

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1 - you said in the first pic you embeded that rigid Diaphrgm rely on rigid links rather than on finit elements which is what i noticed when i was defining the calculation model for the panel so if it relies on rigid links how can i get the value of My and Mx in the panel using rigid links method ?

If you decided against generating the mesh on a panel you decided that you are not interested in the slab deformation under the vertical load (you need to have mesh generated to see maps of e.g. bending).

2 - if i would follow you second sugession which is to use stiffness in XY plane which is similar to flexible diaphragm i will get lower results for My in the core wall ( almost half the value if i would use rigid diaphragm ) and i wanted to get the worst case for designing the core wall.

so is it possible to have a full rigid diaphragm to be able to get the worst case for core wall and in the same time get results of My and Mx for the rigid floor??

If you generate rigid links with all d.o.fs fixed for all nodes of a slab (including the vertical displacements) you do not allow for any bending.

3 - regarding the core wall question i was asking if that diagram for the moment of the core wall looks correct ? this is the first time i use robot to design core wall so i was thinking may be it will show each core wall seperate as a cantilever bar .

This is correct (they should look like two diagrams on a separate 'bars'). Looking at the picture you attached I can see that in fact you have such two separate diagrams but I'm not sure what you displayed - is it the envelope of results or are they the diagram for selected single load case / combination?

**Artur Kosakowski**