SAP mesh/constraint problem

[TheSage]

Hello, I am new to these forums, I came across it looking into my problem but didn't find the solution so might as well ask

I am new to SAP but have to use it for this assignment. I am doing seismic analysis of a already built building and the number of finite elements is pretty big so the calculations are really slow and it makes sap crash and give out errors. So I looked around and people are mentioning constraints for modeling symmetrical buildings that make calculation time shorter. I am attaching an image of the building in question (it is symmetrical about the y plane).

1. How should I use the constraint elements? Do i just delete half the building and put elements somewhere? Where should I do it, and what type of constraints should I use (body?) And what options should be turned on, meaning which directions should I choose, x,y,z etc.

2. What does using constraints mean for my calculation results? Should the modal analysis periods be the same as with the whole building? What about displacements?

I also have some general questions about sap:

3. Is it ok to just mesh big elements, or do I need to do it myself by dividing areas? I have done it myself but now I am wondering if that was a good idea? If SAP does it do the elements connect well to each other (floors to walls etc.) because I had a lot of problems where a wall was not connected to the floor or to another perpendicular wall so it was moving on its own in the modal analysis.

4. What size of elements should I use? I divided them to be less than 0.5 meters but don't know if that is enough/too much. Again, I didn't mesh the structure but divided it, and my model runs really slow.

5. Is there a way to look at base reactions other than in a Table? When I try opening the table I get an error saying "Error creating database file" so I can't see the reaction for the seismic load.

Thank you for your help in advance

 

[IJR]

I did not look at your jpeg but here is my advise.

-Use frame elements as much as you can, avoid shells unless necessary.
-Study a bit about constraints so that you understand what you are doing. Constraints are used to make a set of points move a certain way. There are so many of those certain ways, so be careful what constraints you are using. Your friends are probably suggesting that you use floor diaphragm constraints. If that is true, then you can choose a set of points ON A FLOOR and assign a diaphragm constraint. Make sure that no other joints are assigned that very same constraint. If you have more floors, then use a constraint for each floor separately.
-Use CSI website videos to learn about constraints

hope this helps

 

[kostast88]

1. You use constraints where you need them or where they are necessary. As IJR said, a little study is necessary on them.If what I see on this image is shell elements, then prefer a Weld constraint,which defines a master node, and all slave nodes in a user defined radius (tolerance) is forced to behave exactly like the master node (to the degrees of freedom that you define). If your model does not converge, then constraints are more than necessary.Connectivity is also defined by them.

2.Enslaving nodes to a master node for the predefined DOFs, eliminate these DOFs.Less unknowns to the equations...simpler and faster.

5. Yes, show plot functions->Baseshear.