Precast concrete floor without reinforced concrete topping [FC4]

Precast concrete units without reinforced concrete topping. Precast units include hollow-core slabs, solid slabs, or a system of precast concrete joists with timber or hollow concrete infill.

Precast concrete hollow core slabs (tropicalconcrete.com)

Concrete floors consisting of hollow core slabs with inadequate connections collapsed in the 2008 Wenchuan, China earthquake (J. Dai)

Precast concrete hollow floor slab supported by concrete block masonry walls, Canada (J. Adams)