Ordinary continuous direct foundations, inverted beams and slab foundations


Continuous foundations have the primary function of uniformly distributing on the ground the loads transmitted by the overlying load-bearing structures - for example reinforced concrete walls or brick or stone walls - by means of the enlargement of the support section which allows the stresses to be contained within the safety limits of the terrain.

A very important element in foundations is the lean concrete, which is a layer of lean concrete of limited thickness. This creates a clean and level support surface, which facilitates the formation of the metal reinforcement and formwork. If of adequate thickness it can perform static and load distribution functions.



fondazione continua in calcestruzzo non armato, eseguita con il getto entro casseri

If you have fairly solid ground, and if the loads to which you subject it are not excessively high, you can resort to continuous foundations of unreinforced concrete, created by casting in the formwork or in the same excavation with a fixed section (to find out more the more you see here. 

In both cases it is advisable to gradually widen the base by means of recesses set at an inclination of approximately 60°, making bending and shear stresses of little importance.

In the case of a continuous foundation in unreinforced concrete cast directly into the foundation excavation, a trapezoidal shaped section is obtained, where the smaller base will be the lower one.

The greater quantity of concrete required is compensated by the saving in the formwork required for casting.


To complete the foundation, it is recommended to create a reinforced concrete curb (the curb is a concrete element inserted throughout the entire thickness of the wall in correspondence with the imposition plane of the attic) in order to improve the connection with the base of the structure .

fondazione continua in calcestruzzo non armato, gettata nello scavo di fondazione



fondazione continua in calcestruzzo armato

The ability of reinforced concrete to resist bending stresses allows the creation of less massive foundations than non-reinforced concrete, which are called cantilever foundations (or raft foundations). They are formed by a continuous curb with two lateral brackets made of reinforced concrete, in order to absorb shear and bending stresses.


In the case of less resistant soil, it is the most suitable type of foundation, in fact it requires a smaller quantity of concrete, reducing its weight. As a counterpart, it requires more work in relation to the formation of the metal reinforcement and the formwork.



fondazioni a trave rovesce

Inverted beams are very useful structural elements, in fact they are beams made of reinforced concrete which allow the loads transmitted by the pillars to be distributed. A peculiarity of these beams is that they have an inverted T-shape, equipped with two lower slabs (or brackets), with the task of widening the surface that rests on the ground.

This type of beams are used above all in the presence of frame structures, and above all when large support surfaces are required and the ground does not have uniform resistance. 

Their implementation involves different and successive phases:

1) a first layer of lean concrete;

2) the subsequent formation of the metal armor;

3) the casting of the beam slabs;

4) once the mix has hardened, the containment sides are mounted and the upper part is cast, which is called the core.



fondazione a travi rovesce incrociate con struttura a telaio

The succession of numerous inverted beams, aligned with each other according to the rows of the pillars, produces a static scheme of continuous beams on multiple supports, which are oriented according to one of the sides of the building's plan and joined by transverse stiffening curbs.

Crossed inverted beams are formed when the stiffening stringers also become inverted beams. This happens if it is necessary to make the foundation more rigid. This allows for adequate load distribution.

It is very advantageous to create inverted beams with a high height/base ratio, which allows a reduction in the reinforcement and stresses to which the concrete is subjected.




fondazioni a platea

It is used when the ground is not able to withstand the loads deriving from the structure. In this case the inverted beams, which would be too wide, are replaced by a single reinforced concrete base slab of suitable thickness. This is called a plate foundation.

In addition, main and secondary beams can be provided between them to further stiffen the slab. They will protrude between them, forming what is called an inverted ribbed plate, with the flat surface facing downwards.

The advantages are the efficient distribution of loads and good structural continuity, and in the presence of non-uniformly yielding soils. A disadvantage is the greater quantity of material needed.

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