The floor slabs, also colloquially referred to as filigree floors or half-finished slabs, are used in residential and industrial construction.
The floor slabs are preferrably used in combination with double walls to create monolithic constructions and are characterised by their low weight. This enables the semi-finished precast parts to be installed on the construction sites, using cranes with lower load capacities.
As a result of the low weight / volume, the transport costs to the construction sites are correspondingly lower than for solid precast concrete slabs.
The floor slabs normally consist of a 40 - 60 mm thick concrete board, longitudinal and transverse reinforcement and trusses in a lateral direction. The trusses consist of welded concrete steel, the visible top member bars, two concrete cast bottom chord members and the diagonals between the top and lower members. The top surface of the slab is left in a untreated state which, in conjunction with the diagonal chairs, creates perfect bonding between the precast parts and in-situ concrete.
Mounting parts such as electric sockets, wiring, openings, etc. can be already installed in the floor slabs in the precast concrete plants. Following positioning on site, extra reinforcing bars are inserted through the support chairs.Supplementary reinforcement is required where the slabs but against each other. This lateral reinforcement must be fastened so, that it cannot be displaced during on site concreting operations. Furthermore, it must not lie directly on the finished surface, but must exhibit a concrete cover corresponding to the application for the purpose of sufficient durability to the finished part.
Empty conduits for electrical wiring are also added, after it is concreted with in-situ concrete/ concrete top layer. The floor slabs must be supported during the concrete curing process. This is classed as lost formwork and the underside of the floor slab is characterised by its high surface quality = the underside of the slab is designed for the direct applications of wallpaper and paint. Plasterwork is not required, the joints between the individual slabs (up to 3 m wide) must be filled.
Facts
Concrete board: normally 40–60 mm thick
Length: up to 10–12 m
Width: normally up to 3 m, depending on the transport possibilities to the construction site.
