It would help to know the context of the term in question. The most straightforward translation of the term seems rather cumbersome and I'm not entirely sure if it would be framed like that in Norwegian.

To break it down:

Monolithic - Monolittisk (something that is solid or in one piece)
Rib-and-slab - Hulldekke (a type of concrete construction with empty spaces inside the construction, like on the picture attached)
Floor - Gulv (explanation unneccessary)