If it is a simple rectangular floor then you could create a complex profile wall or beam (beam is probably better).
The profile will be the width of your slab with all the recesses and you stretch the profile beam the length you want the slab to be.
Or maybe there is an object out there that does this - i am not aware of any in particular though.
Or just model a very thick slab.
Model smaller slabs or morphs in the shape of the voids.
Use Solid Element Operations to subtract the voids from the main slab.
Hide the void slabs/morphs in a layer that you can turn off so you don't see them.
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