Corbelling

Arch dry stones encorbellées and inclined towards outside

The stone vault encorbellées and inclined towards the outside was concretized in this type of rural architecture which are the dry stone huts. That they are huts of France or other European countries, it was systematically employed by the peasants car-manufacturers or the masons with dry stone of both or last three centuries to cover space with the lower costs in buildings being used as agricultural appendices within the farm or in pieces very distant from this one (open huts).

This type of vault, built on a basis derived from the circle, rests on two principles: the “corbelling” and the “slope towards outside”. The principle of the “ corbelling ” consists in laying out the stones of the same circular base in overhang compared to those of lower base, with the manner of corbels. It is imperative that each stone does not exceed out of its own center of gravity the subjacent stone, in order not to rock. With this intention, it is enough to give to each corbel a sufficient tail as a counterweight, and to attenuate the weight of projecting by reducing it. Another need is to cut the corbels in form of sector so that their interfaces radiate towards the center of the circle.

The principle of the “ slope towards outside ” consists in printing with the stones of each base a light slope (about 15°) towards outside (if they were posed horizontally, one would have strictly speaking, a vault in “heap-of-load”, made of sat with horizontal beds). This dip involves a horizontal jamming between the plates of the same base and the closing of a polygon of forces: each base is then clavée horizontally and holds alone, while resting on the preceding one. The horizontal thrust towards outside exerted by each base is cancelled while laying out, with the back of this one, a material mass playing a part of thrust.

Successive bases, because of the shift towards the interior, are meeting, last base being capped either with a final flagstone or several juxtaposed flagstones. No clotheshanger is necessary in this vault to horizontal effects (contrary to the traditional vault clavée which, it, is for vertical purposes). As for the final flagstone, it can be removed without causing the collapse of the vault (contrary to the key of a clavée vault, whose fall involves the collapse of the unit).

Whatever the type of dry stone vault, one will not forget the fact that it itself is covered either with a cover of flagstones or lauses which marries the form of it, or of a stone coating according to the technique known as of the “double skin”.

It is not necessary to oppose encorbellée vault and arches clavée, by qualifying the first of “blind arch” in opposition to the second, the only one to deserve to be called “vault”. In fact, the expression “blind arch” couvrement indicates only one not built (for example out of painted wood) imitating the provision and the appearance of a built vault. The encorbellée vault must be regarded as a system of voûtement with whole share, a “horizontal” vault, in opposition to the “vertical” vault.

Construction of bridges

With regard to construction in corbelling in the bridges, noncurrent works of art line up, roughly speaking, in two big families:

the mixed Viaduct S steel/concrete (standard Millau)
works any concrete.

For the first, the supports are in Reinforced concrete whereas the apron, out of metal, is generally set up by launching since one of two banks or from both, as it was the case for the Viaduc of Millau.

In the second category, the work consists of a concrete apron which is built by successive corbellings. The elements of the apron, called Voussoir S, are cast places then assembled the ones from there at the others, to constitute part of apron which one calls Fléau (as on a balance, the apron being presented, in constructive phase, like a gigantic plague in balance on its pile). In practice construction starts by the realization of the voussoir on pile (VSP) which constitutes the natural prolongation of the pile and the first element of the apron. It is a hybrid part, complexes to realize, which ensures the transition from the efforts between the apron and the pile. Once this first completed element, construction continues symmetrically compared to the pile, in order to ensure the balance of the gigantic balance, the voussoirs being concreted in full sky, often under difficult and rigorous work conditions, using a tool called moving element. As work is carried out out of mirror, at each end of plague, the progression requires a pair of moving elements which are moved once each finished voussoir. The concreting is carried out via a crane, which ensures the provisioning by bucket, the voussoirs being connected the ones to the others by prestressed in order to rigidifying the apron. Each pile sees its half-plagues thus progressing to join those of the close piles, the operation of junction of the two parts of apron, baptized Clavage, being carried out via a baptized element, logically, voussoir of keying-up.

See too

the Prieuré of Saint-Arnoult presents a frontage of XV°siécle to double corbelling.

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