Most common types of floors in residential buildings
In the world of construction, there are many types of slabs, and, when referring to the most common, we mention those that we can find more frequently in residential construction. Mainly, a general classification must be made between two large groups of floors, the unidirectional and the bidirectional:
-The unidirectional floors are those that need supports at two of their ends, for example, the beams, to transmit the load to the columns, and from there to the foundation.
-Bidirectional floors do not need end supports for the loads. Still, the loads are transmitted in both directions, creating a lattice up to the columns.
Within this classification, we find different subcategories. The first to be discussed is the one-way slab of joists and vaults, which is the most used method in a residential building in Spain. In this type of floor, the joists (precast concrete elements with prestressed reinforcement) are responsible for transmitting loads from the bottom to the beams. For the transmission to be useful towards the rays, there must be a connection between the parts, for example, by inserting the joists into the beams.
The strength of this type of slab is clearly based on the joists, so the space between them is hardly relevant in terms of load-bearing capacity, so there is no need for a complete concrete mass between two joists. To eliminate the own weight of the joists, lightening elements are placed supported between two joists: the vaults. These are usually made of concrete, although they can also be used in other materials to lighten the weight further.
Another type of unidirectional slab is that of joists in situ. This is widely used in floors with complex geometries, as it can be adjusted to the centimetre, although it is more complicated to execute. Besides, since they are not precast joists, the reinforcement is not prestressed, so it does not have as much resistance.
There is also the unidirectional slab of a collaborative sheet, which is very useful in metal structures since the placement of joists and vaults can be somewhat complicated. The sheet metal has folds that give it the shape of grooves, which once filled with concrete, provide it with inertia. This system has the advantage of the speed of laying the plates and that it is a lighter slab than the traditional one. Its disadvantages include that it is necessary to place connection elements between the leaves, the use of tools for nailing the plate against the metal structure is required. The placement of holes for the passage of floors is complicated as it is not a flat surface.
Finally, it is worth mentioning the forging of hollow structural bodies, works in a lattice, so it does not need support elements at two of the opposite ends in the direction of the loads. This gives an advantage in terms of the spans that are achieved between supports since the neutral zone of the thickness of the slab is occupied by hollow recycled plastic "balls" that weigh hardly anything and prevent their volume from being occupied by concrete. The execution of this type of slab is quite fast, but the main advantage is the reduction of the structure's own weight without increasing the cost of the system used. In addition, not only the extra cost of the execution and the optimization of the amount of concrete required by calculation is saved (less weight, less foundation volume) but also the amount of concrete is saved thanks to the volume occupied by the hollow bodies. Of course, it is a more specialized calculation since the hollow balls tend to float when pouring the concrete.