Modeling holes in diaphragms

[BubbaJ]

How do you model a hole in a floor diaphragm for a stair or elevator shaft?

Is this accomplished by merely detaching the joints around the hole from the diaphragm?

Or is it not necessary as there is no framing in the hole to transfer forces?

 

[JoshPlumSE]

Bubba -

It depends on how the diaphragm is modeled. If you are using the "rigid diaphragm" feature in RISA then you would do as you suggest and select all the joints in the hole and designate that they "detach from diaphragm". The only problem with this is that the RIGID diaphragm is very rigid as the name implies and the diaphragm will still behave rigidly... it just won't be connected to those joints.

If, however, you are more interested in the forces in the diaphragm in the vicinity of the opening then you would probably want to model the diaprhagm using plate elements. That way, you can see exactly what forces occur around the opening.