Ribbed vault

“ There was still one difficulty, however, one slight failure both practical and theoretical in the vault architecture, which for a long time much exercised the minds of the builders. The ribs of the vaulting being all of unequal length, they had to assume different curves almost immediately on rising from the impost; and as the mouldings of the ribs have to be run into each other ("mitered" is the technical term) on the impost, there not being room to receive them all separately, it was almost impossible to get them to make their divergence from each other in a completely symmetrical manner ”

“ In the earlier examples there are ribs on the angles of the groins only; at a later period the vaulting becomes more complicated, as at Westminster. There is a longitudinal rib, and a cross rib along the ridge of the cross vaults, and frequently also an intermediate rib on the surface of the vault. The bosses are rare at first, more abundant afterwards: they are generally well worked and enriched with foliage. English vaults are sometimes of wood only, as in York Minster, and the cloisters at Lincoln. A vault is, in fact, a ceil{xxi}ing, having always an outer roof over it. ”

“ VAULT [1] (Fr. voute, Ital. volta, Ger. Gavolbe) , in architecture, the term given to the covering over of a space with stone or brick in arched form, the component parts of which exert a thrust and necessitate a counter resistance. In the case of vaults built under the level of the ground, the latter gave all that was required, but, when raised aloft, various expedients had to be employed, such as great thickness of walls in the case of barrel or continuous vaults, and cross walls or buttresses when intersecting vaults were employed. ”

“ There is nothing now to indicate that the provision of a vault had been intended by the original builders of these walls. This deficiency was met by the insertion of vaulting shafts and the addition of external buttressing; for as the pressure of the flat wooden roof was exerted for the most part vertically upon its supports, that of the vault would be a strong lateral thrust as well as vertical pressure, and these were to be provided for. ”

“ Vaults were built sometimes of brick, sometimes of cut stone; in a few cases even of earthenware jars fitting into each other, and laid up in a continuous contracting spiral from the base to the crown of a dome, as in San Vitale at 123 Ravenna. Ingenious processes for building vaults without centrings were made use of—processes inherited from the drain-builders of ancient Assyria, and still in vogue in Armenia, Persia, and Asia Minor. The groined vault was common, but always approximated the form of a dome, by a longitudinal convexity upward in the intersecting vaults. ”

“ Such floors exposed the keep to be burned, and once well on fire it would certainly burn till it was gutted. The basement is now and then vaulted, but the vaulting is very rarely original, and when it is so the keep is late. The vaulting at the Tower and at Dover is modern brickwork; the Ludlow vault seems Early English; that at the lower part of Carlisle, that of Porchester, Brougham, Bowes, and Richmond, Decorated; the vaulting at Middleham, Newcastle, and Mitford may be original. ”

“ The slight increase in mass quite suffices to account in the interior for the principal roof timber which rests upon it, and, with the vaulting-shaft, to continue upward the line of the nave-pier. But if the flying buttress, necessary to transfer the thrust of the vault, were built at this point, the arcade of the exterior would be effectually interrupted, and the space between the buttresses set off into a single bay, as in the wall of the aisle below, which does, in fact, represent a vault. ”

“ The simplest kind of vault is that known as the barrel, wagon Or tunnel vault, which is generally semicircular in section, and may be regarded as a continuous arch, the length of which is in excess of its diameter; like the arch (q.v.) , the same provision is required as regards its temporary support whilst the voussoirs constituting one of its rings are being placed in position, for until the upper voussoir, or keystone, is introduced it is not self-supporting. ”

“ The groin-ribs, intersecting at the centre of the vault, divided each bay into four triangular portions, or compartments, each of which was really an independent vault which could be separately constructed upon light centrings supported by the groin-ribs themselves. This principle, though identical in essence with the Roman system of brick skeleton-ribs for concrete vaults, was, in application and detail, superior to it, both from the scientific and artistic point of view. The ribs, richly moulded, became, in the hands of the Gothic architects, important decorative features. ”

“ Their use is to strengthen the angles of the dome, and to augment its power of resistance to the weight of the lantern which crowns it. They do not support the vault as the ribs of a Gothic vault do. Being composed of very deep voussoirs, they have more strength to withstand thrusts, as well as to bear crushing weight, than the enclosing shells have, and thus to some extent they may hold these shells in. ”

“ This great space is covered by an immense vault, upheld by no central shaft; arches are thrown across the corners bringing the square to an octagon, and though not very high, it is one of the boldest Gothic vaults ever attempted; there is nowhere else a room of such a size vaulted without supporting piers, and probably none where the buttresses outside, with their small projection, look so unequal to the work they have to do, yet this vault has successfully withstood more than one earthquake. ”

“ It is the merit of groined vaulting that it emphasises the division into bays, and is capable of great richness of structural decoration. On the other hand, it involves a great loss of height, for the ridge of the vault can be little higher than the top of the clerestory windows, and it cuts off the whole space covered by the roof above it from the building which it covers. ”

“ The fluted dome over room A is bracketed across the corners of the rectangular substructure (Fig. 88) . In several cases where a barrel vault terminates not against a head wall, but against another section of barrel vault, it is adjusted to the angles of the substructure{154} by means of squinch arches (Fig. 99) . A noticeable feature of the vault construction of Ukheiḍir is the presence of masonry tubes running between the parallel barrel vaults (Fig. 100) . ”

“ Do you know that if that vault is taken by either an electric-arc or an oxy-acetylene blow-pipe, I will be suspected?”
“I didn’t think of that.”
“It is a fact! You see the police and the private agencies know a man by his work. How can we take that vault in a new way? How can I go through three layers of vanadium steel?” ”

“ Not more than three feet thick, they rise up to a height of nearly seventy feet to support a great stone vault. Four only of the six stand clear from floor to roof, for the two western are embedded at the bottom in the jambs of the gallery arches. From their capitals the vaulting ribs spread out in every direction, being constructively not unlike an English fan vault, and covering the whole roof with a network of lines. The piers are round, stand on round moulded pedestals, and are divided into narrow strips by eight small shafts. ”

“ The vaulting has wall- [114] ribs, cross-springers, and groin-ribs, and is rather high-pitched. Upon the cross-springers the mouldings are a large keeled round having on either side a hollow between fillets, while the groin-ribs are moulded as in the Markenfield Chapel. In the westernmost bay the vault has shown signs of weakness (like so many other parts of the building adjacent to the ill-fated tower) and has been strengthened by a cross-arch with a half-arch abutting against it on the west side, both springing from corbels. ”

“ Through a small opening in the outer shell, near its crown, the hand may be thrust into the void, but nothing can be reached. It is a curious form of double vault, and differs fundamentally from the great double dome of the cathedral. The scheme as a whole is structurally inconsistent; for while the inner vault has the concentrated thrusts of Gothic construction, these thrusts are met by the enclosing drum, and not by the isolated abutments that the vault logically calls for. ”

“ The Construction of enriched Stucco Vaults. When walls have reached the point where the arches of brick or light stone or tufa have to spring, it is necessary to turn a centering with planks in a close circle, over the framework of struts or boarding. The planks are fitted together according to the form of the vault, or in the shape of a boat, and this centering for the vaults must be fixed with strong props in whatever mode you wish, so that the material above does not strain it by its weight ”

“ This form of vault was of very frequent use, though{187} the exact method of filling in the spaces was not rigidly adhered to. Its disadvantages are, that it either limits the height of the walls available for windows, or runs up so high into the roof as to interfere with its construction. It is in many cases, however, a very convenient, as it is a very sightly, form of vaulting.
Even the simple form of vaulting with level ridges is not always convenient for windows, particularly in clerestories, where they have often to fill the whole space. ”

“ The line of intersection is necessarily weak, and the vault requires aid to make it perfect in construction; and this can only be given it in the form of increased thickness, which is at once obtained by altering the form of the pier from a square to a cross form, and applying to the vault the same principle of divided orders as we have done before to arches (Fig. 236) ; only that, in this case the upper order is a vault, and the lower one only an arched rib coming in to aid the{80} vault. The groined vault is thus divided into compartments, and beauty and strength at once provided for. ”

“ FAN-VAULTING. The next step in the process may be observed in the vaults of the choir of Oxford Cathedral (Christ Church) , of the retro-choir of Peterborough, of the cloisters of Gloucester, and many other examples. The diverging ribs being made of uniform curvature, the severeys (the inverted pyramidal vaulting-masses springing from each support) became a species of concave conoids, meeting at the 223 ridge in such a way as to leave a series of flat lozenge-shaped spaces at the summit of the vault (Fig. 136) . ”

“ It is always very difficult to decorate. The fifteenth century builders having for some reason or other decided on the form, and being but little accustomed to it, determined to treat it like a vault. They covered it with a network of ribs, and where these ribs met they placed bosses. They also caused these ribs, as far as possible, to take the same direction that the structure of a real vault would give to them. No doubt the ribs serve some useful purpose as a support to the roof, especially as that roof is slightly pointed and not circular, like the barrel roof proper ”

“ Q. Of what description was the Norman vaulting?
A. The bays of vaulting were generally either squares or parallelograms, though sometimes not rectangular in shape, and each was divided into four concave vaulting cells by diagonal and intersecting groins, thus forming what is called a quadripartite vault. Early in the style the diagonal [64] edges of the groins appear without ribs or mouldings; at an advanced stage they are supported by square-edged ribs of cut stone; and late in the style the ribs and groins are faced with roll or cylinder mouldings. ”

“ It should be noticed that fan-tracery vaulting is peculiarly English, the principle of it began with the earliest English Gothic style, as in the cloisters of Lincoln Cathedral, each stone of the vaulting being cut to fit its place. In France this is never done, each block of stone is oblong, as in those for the walls, and is only made to curve over in a vault by the mortar between the joints. This had the effect of making vaulting much cheaper to construct, and therefore much more abundant in France than in England, but it is always less scientific and often less beautiful ”

“ A description of the vault will be found interesting to many. The wall of the vault rests upon the natural surface of the ground, about three feet high and eight and a half feet square, the inside corners being slightly rounded; it is built in layers about four inches in thickness and varying in length upward to three feet, neither cement nor mortar being used in the joints ”

“ The most normal and readily invented vault is that of the continuous barrel or demi-cylindrical form, covering an oblong building from end to end, and the{52} most readily conceived idea, where the building has to be roofed over such a vault, is to fill in the space between the arch and the triangle of the roof solid, and make it at once the ceiling of the room and the support of the roof covering. ”

“ Within this stone inclosure was a large and roomy vault, half filled with cases, barrels, and packages, and at the upper angle was a narrow subterranean vaulted passage, barred also by an iron-bound door, which led to a succession of whitewashed chambers––dark, damp, and gloomy––and then on, in a fissure-like pathway, to another equally strongly secured outlet on the other side of the crag. Leading to the veranda was a tautly-stretched rope ladder lashed to eye-bolts let into the natural rock below, and hooked on to the edge of the floor above. ”