Building Techniques : C6 – Barrel vault Country : Tunisia PRÉSENTATION Geographical Influence Definition Barrel vault - Horizontal framework, semi-cylindrical shape resting on load-bearing walls - For the building, use or not of a formwork or formwork supports. - Used as passage way or as roofing (in this case, the extrados is protected by a rendering). Environment One finds the barrel vault in the majority of the Mediterranean countries studied. This structure is usually used in all types of environment: urban, rural, plain, mountain or seaside. Associated floors: Barrel vaults are used for basement, intermediary and ground floors for buildings and public structures. This technique is sometimes used for construction of different floors. In Tunisia, stone barrel vaults are only found in urban environment, they are common in plains and sea side plains, exceptional in mountain. The brick barrel vault is often a standard in mountain environment. The drop vault (rear D' Fakroun) is often a standard everywhere. Associated floors: In Tunisia, this construction technique is used to build cellars, basements, cisterns (“ fesqiya ”, ground floors and first floors (“ ghorfa ”). Drop arches and brick vaults can sometimes be found on top floors. Illustrations General views : Detail close-up : This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States 1/6 C6 Tunisia – Barrel vault CONSTRUCTION PRINCIPLE Materials Illustrations Nature and availability (shape in which it is found) For the construction of barrel vaults, the most often used materials are limestone and terracotta brick in all the studied countries. Other kinds of stones are also used according to the local availability in materials ( schist and granite...). The materials added for the filling of the interstices of the extrados, or for the composition of mortars are: broken brick, lime, gypsum plaster, gravel or pieces of broken pots and coal debris. Earth and stone are the materials used in Tunisia to build stone barrel vaults, the filling materials are plaster, lime mortar and coal debris. The brick vault is built with solid terracotta, plaster, lime mortar and hollow brick. The vault in D' Fakroun is carried out with the same materials as above. Modules, Dimensions, Dose ratio The barrel vault is masonry laid in mortar: the modules are assembled one against the other according to a sloped plane determined by a radiant wire that shows the angle of each section from the bottom of the vault to the key, and from the center of the arc. The stone or brick modules which make up the vault can be cut so as to form a specific key for the vault (2 tilted Barrel vault in stone faces make up both a stone course and a bearing surface). They are often hardly outlined in flat stone: mortar catches up any irregularities showing on the surface. Type of laying Type of laying, use of a formwork, formwork supports The building of the vault is generally carried out using a wooden formwork. The latter is composed of at least two trusses (section of the vault), on which one fixes laths of wood (sole-piece), the outside shapes the intrados of the vault. The formwork can also produce a more approximate shape, which is then corrected with a bed of earth or sand... Anchored directly in the walls (cross beam, retractable) or supported by bolders (projecting stones left in place after laying ), this unit constituting " the formwork " is held by supports. Barrel vault in cave The laying of stones and bricks is made from the springer to the key by balancing the loads on Mosquee in Kasba (Sfax) both sides of the vault axis. In the Mediterranean area, some techniques are freed from this formwork system (low wood supplies? tools are considered as overly cumbersome?, particular and local know-how?...). Building without formworks is possible with regular shaped modules (terracotta brick, cut or not), well prepared mortars (adherence of bricks, hardening speed...) and with a particular laying method. The latter seeks to limit the overhang of a key stacking, by creating intermediary support joints, by slanting the laying axis (springer/key/crown) towards the walls. In Tunisia, the barrel vaults can be up to six meters long, they are laid with mortar, using a formwork "built from scratch" : this formwork is a full length structure, made with wooden elements, superimposed stone, rubble and sand to adjust the shape. The brick barrel vault one can be built without a formwork if plaster is the binding material, or with formwork if the binding material is lime mortar. The drop vault “ Dh' har Fakroun ” (literally: tortoise back), whose layout arrow is lower by half a span, is build with or without a formwork according to the nature of the binding material. Details in " Realization " section. Tools In addition to traditional mason tools, no particular tool is necessary for the building of the vault in throughout the studied countries. Physical (span...) Space covered with barrel vaults at the clothing souk. This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States 2/6 C6 Tunisia – Barrel vault CONSTRUCTION PRINCIPLE (CONTINUED) Trades Illustrations Trade, Number of people necessary The barrel vault is exclusively carried out by experts, mason, mason/stone cutter, or stone cutter helped by assistants (significant handling, mortar to prepare...), and sometimes assisted by a carpenter for the realization of the formwork. In Tunisia, the barrel vault is carried out by a mason helped by two workmen. Performances Physical (span...). This construction technique leads to span widths that range from 1 to 7 meters, for a thickness that varies from 30 to 50 centimeters and can even reach 1 meter on the edges of the vault in Tunisia. In Tunisia, the usual span of for stone barrel vaults found in various types of construction Construction principle : construction (cellars, rooms, shops, ghorfa on a higher floor) is between 2 and 3 meters. As for the technique of a vault without armature thickness of this framework, it is about 40 cm on the level of the axis of the vault and can reach 1 meter on its sides. The common span for drop vaults and brick barrel vaults is between 3 and 6 meters, for an average thickness of about 25 cm. Thermal - Acoustic. For a stone construction, limestone in particular, the thermal and acoustic performances have been reported from rather good to excellent by all the countries concerned. Considering the significant mass of the vault, its thickness, the materials used in its construction, this piece of work has remarkable thermal and acoustic insulation qualities. In Tunisia, this enormous horizontal structure is a relatively light mass thanks to the hollow bodies which fill its sides, framed by a " Nasriy a " masonry: it is laid in stone with lime mortar and ensures excellent thermal and acoustic performance. Regarded as the best technical solution in the areas concerned. Brick barrel vault without armature Construction principle : thermal - acoustic Construction principle : materials, thermal - acoustic – vertical section This project is financed by the MEDA programme of the European Union. The opinions expressed in the present document do not necessarily reflect the position of the European Union or of its member States 3/6 C6 Tunisia – Barrel vault ASPECT, PATHOLOGY Aspect Illustrations Finishing, associated roofing. The intrados of the vault is generally covered with a rendering. However, in the case of ashlar vaults or carefully laid bricks, the facing can be left bare. In the case of a vault for a passage way, the extrados of the vault generally does not get any particular processing; haunches are frequently filled with various materials (quarry rubble, building site residue), the unit gets a system to seal the ground. In the case of a roofing vault, the extrados of the vault has regular lines, and receives an elaborate waterproofing rendering. In Tunisia, the barrel vault stone is never apparent outside, it is always protected by flat a terrace known as " tah ". It is initially surrounded by an enclosing wall called " Nasriya ". One fills the wings of the vault with unusable pottery: this contributes to greatly reducing the weight of the roof terrace. One then determines the shape of the slope with three successive sand layers of wadi, lime concrete, and finally a layer of smoothed rendering. Two types of coating are reported for the brick barrel vault: either it gets a light renewal rendering, or it is completely embanked and the roof is thus transformed into a flat terrace. As for the drop vault, shape contributes to the protection and the waterproofing, allowing Ageing Pathology rainwater run-off; but this waterproofing is also ensured by two to three layers of whitewash applied on the second stone or brick layer. This is renewed each year, but one can also transform the flat roof by filling it with earth or light " quarry rubble ": one then applies the layers of mortar for the floor, or shapes the slope if this roof is used as a superstructure. Ageing pathology Linked to materials and climatic conditions : As for stone or brick masonry, pathologies related to materials originate in water (capillarity, infiltration, condensation...), which dissolves the mortars and weakens them. The control of water infiltration is more significant in the case of the vaults; Beyond the dissolution of the mortars it is necessary to note direct erosion, that can affect the rendering mortars. In Tunisia, one has seldom found a completely collapsed barrel vault, which proves its great resistance.