Analysis using door opening in shell elements ?!?

[popabf]

Hi to everyone!
I tried to analyse (static and dynamic/modal) a 3D reinforced concrete frame structure having also walls and floors.
The problems ("analysis incomplete" or "zero stiffness for joint..in direction ...") appeared when I meshed the walls. After meshing, I deleted some of the small shell elements created by meshing, in order to create a door opening.
I tried all types of constraints for joints diaphragms->auto; plate constraint; weld constraint; etc.) so I can model the behavior of the walls with openings. Always the program said : posibility of mechanism "or" stiffness is zero (for the nodes created by meshing the shells....)
What kind of constraints or other properties should I define in order to perform an analysis having openings in walls?
P.S.: I tried a simple model (2 stories, 1 bay on X and 1 bay on Y) and I defined the walls as Shell->Membrane. The analysis went well, but the results (stresses in the walls) were "general". So I meshed the walls 2x4. After that, the analysis gave me the errors presented above. When I meshed the walls 1x4, I had no errors.
It seems that SAP2000 v.8.12 can't provide me some dense meshing. Only if I define meshes like 1(horizontal) x "n"(vertical).
Thanks for reading these and patience.

 

[popabf]

It seems that only using shell->shell and not shell->membrane/plate to define the walls or floors doesn't give any errors. And I didn't use any constraints. Are they necessary, yet?

 

[shakildor]

Dear POPAUF,
To model a frame structure with slab and walls , first start with simple model using frame members only. Then Add shell members as necesary. BUt be carefull about one thing. If walls are not of concrete and are not monolithic with surrounding beams and columns, you can not model masonry walls as shell. Lets say that your walls are of concrete and monolithic with other concrete frame members.

After modelling the wall,upto this point, the SAP will assume that teh connection between shell and frame is at the end nodes only. SO the DL or LL applied on sheel will not be transfered to beams, but transfered to colomn directly as the case may be.

So, now you have to mesh the shell. You can mesh it into any numbers as you want(but remember ..increasing the numbers of shell will increase the complexity of the problem and solution may take longer ...even may 30 minutes...so usually the divide the shell so that each mesh is size of 1.0 m x 1.0 m to 1.5 m x 1.5 m ).

Now you have to divide the surrounding beams and columns also as per the adjoining nodes of the connecting shell. In SAP there is a simple command for that.

NOw only the effect of slab or wall representd by shell will be transfered to the surounding beams and columns.

If you are representing the concrete slab and shear wall, then make shell a shell (not thick plate or membrane)

Then after you can see the difference in BM and SF of surrounding frame members

Hope it will solve ur problem

 

[popabf]

Thanks, it was helpfull in order to define walls.
What about if we have windows in that walls? I have to delete some of the new small shells created by dividing 1 wall. I gave to the new nodes formed (we are talking about 1 wall)- by dividing the shell- some constraints: diaphragm or body.
Even that so, it takes a lot of time to analyse, and still gives me errors -> zero stiffness for the nodes created by dividing the wall...and periods (from Modal analysis) of 10.000 seconds or so.

 

[shakildor]

Dear POPABF
First you have created wall using several sheel elements and making these connected to surrounding beams and columns(by dividing the beams and columns also)

Then simily remove the shells to represent door or window opening, You dont have to do naything with constrains

ShakilDOR