Rib-and-slab ceilings are ceilings, in which the load-bearing elements (carrying loads) there are prefabricated beams with an axial distance not exceeding 90 cm (in most of the available ceilings, the beam spacing is denser and ranges from 40 do 60 cm). The ceiling beams are usually stretched towards the smaller span of the room, rests on the walls of the building and joists. Filling elements are placed between the beams – ceramic blocks, LECA blocks, gravel concrete blocks, made of lightweight concrete, gypsum or polystyrene fittings. The filling elements play the role of permanent formwork. The upper part of the rib-and-slab ceiling is a concrete slab poured at the construction site – the so-called concrete topping. Concrete poured on the ceiling forms structural ribs along the ceiling beams.
Division of rib-and-slab ceilings with regard to the method of execution:
• Monolityczne, fully concreted (including ribs) on the construction site.
• Monolityczno-prefabrykowane; the ribs are prefabricated, and at the construction site, only concrete topping is poured.
Depending on the type of the floor, the prefabricated joists have the form:
• reinforced concrete beams
• truss steel beams concreted in concrete feet
• ceramic-concrete beams (concrete beams placed in ceramic fittings).
For large-span, rib-and-slab ceilings, whose deflections may be significant, there is a risk of the so-called. "Keying" of the ceiling ribs. To prevent this from happening, transverse separating ribs are used for floors with larger spans.
Reinforced ribs are used under the partition walls that stand parallel to the ceiling joists. They can be made by placing two prefabricated beams side by side or by spreading the beams apart, laying additional reinforcement between them and concreting, thanks to which an additional reinforced concrete beam is obtained at this point.
The main advantage of ribbed ceilings is easy installation, which does not require heavy use, specialized equipment. The disadvantage is that the permissible load is limited to a certain value (depending on the type of the floor).