I'm a student and new user of seismostruct so if you could elucidate about this question i will be grateful.

In my project i have slabs lightened (http://imgur.com/a/qdEDO) that only works in some directions as you can see on this image http://imgur.com/aH1BEd7.
My question is : What is the best way to represent this behaviour? Using Rigid Diaphragms restraint in X-Y or in Y-Z? Or there is a better way to consider this?
Best regards