Joint Link Elements vs. Connection Link Elements

[Mastropower]

Hi everybody,

I am working on a full scale roof diaphram model in SAP2000 Nonlinear 8.5.3. The model uses shells to reprensent the steel deck and frame/cable members to reprensent the actual structure below.

To join the two structures, I am trying to use Link Elements. However, I ask myself if I should use Nodal Link elements or elements linking the nodes of the two "strutures", ie the steel deck and the joists below. I am not very familiar with link elements in SAP, so any help would be much appreciated.

My nodes are one on top of the other for the frame and the steel deck. Any suggestions? This is for a linear pushover analysis by the way.

Thanks

 

[masomenos]

Is there such a thing as a linear pushover analysis?? Are you looking for composite action between deck and joists? You might try looking into using constraints which enable you to connect joints in varying degrees of freedom..in other words, you can control which degrees of freedom to link the deck joints with the joist.

 

[Mastropower]

MasoMenos

Thanks for your input, it helped a lot.

Because you seem to know a lot about constraints, I have a question: I have gap elements between the deck and the joists to prevent any movement of the deck into the frame elements. My frame element is 4" wide, thus i created 3 nodes, all seperated by 2" to reprensent the edges and centerline of the frame member. I assigned a constraint in all directions to these three nodes to simulate the fact that they are on the same frame element. I repeated this method all along the joist. Is this right? Any suggestions?

I have a model which is the same, but without any constraints, and it has a much lower stiffness than that of the previously explained model. I do not understand why this happens.

I hope this is somewhat clear... If not, I will try to insert an image in the next post.

Gracias

 

[masomenos]

Mastropower, if you need to model gaps, please understand that constraints don't have them. Think of a constraint as acting like a very rigid beam with no weight which connects between two or more joints. If you link 3 joints, then of course you are making your model stiffer.

I initially thought you were trying to simulate some sort of composite action between the deck and frame elements. If this does not answer your question, then you might try providing some sort of graphic image.