C),/ina'rica/ or 13arrel Vaults may be regarded as part of a hollow cylin der with an arch-line in any form. All arches in a wall (for example, fig. 12) should be regarded as short, cylindrical vaults. As a ceiling, the cyl indrical vault is generally nsed in long spaces, such as corridors, or in long bays divided up by " transverse arches." A peculiarity of the cylindrical vault is that it transfers its thritst upon only two sides, while it is merely in contact with the other two walls. If there are openings in these resist ing walls, whose crown is on a higher level than the springing of the vault (that is, above the starting-point of the vault), lunettes are built in, which spread—sometimes in an oblique direction—toward a corresponding cut in the main vanit. These lunettes may find application when, like that over the stairs in Figure 17, a vault spans on arcades.
The tnaterial for the cylindrical vault, as for most vaults used for COV ering, is generally brick. The curve of the arch is obtained either by cut ting the bricks, or by making wedge-like heading joints, or by using- spe cially-formed wedge-shaped bricks. The bond will depend on the thick ness of tbe vaulting, which, when carefully carried out, will in most instances require only a half-brick for spans of about 12 feet and less. In this case the bond is a stretcher, but its direction will admit of variation, as the courses (coursing- joints) may run either parallel with or perpendicu larly or diagonally to the axis of the vault.
The Groined is to be regarded as resulting from the interpenetra tion of two cylindrical vaults, with their springings and crowns on the same level. If the lines of .both vaults are to have the satne form, the ground plan of the vault must of necessity be a square. Figure 13 (II. r) exhibits the most simple form of a groined vault of this order, over a quadratic ground-plan; the lines here are those of pointed arches, which, however, are closely akin to the semicircle of the arch-line in the transverse arch. The curved lines (elliptical in semicircular arches) on the under side of the groined vaults, caused by the intersection, are called "g,roins." As a rule, ti.yo arches crossing each other (transverse arches) are first set in the direc tion of the groins, and afterward, between them, the portions of the cylin drical vaults (sectroids); the under side of the transverse arches may either be flush with the surfaces of the vaults (that is, without projection), or, as in the case of Fig-ure 13, made visible in the form of a bead or other pro file, and provided at the crossing-point with a conspicuous keystone boss). If the groined vault be used, not over square plans, but over those which are oblong, either the arch-lines of the intersecting barrel vaults must vary in form, or, at least, if the form be the same, the smaller two portions of the vaults must have a rise toward the vertex. This may be done either
in a straight direction or in a slight curve, and is very frequently extended to all portions of the groined vault.
Groined vaults may be built over apartments which have many sides, whether they are regular or irregular. In this case it is only the number of the cylindrical portions intersecting one another that is increased, and, as regards the common vertex or intersecting point of the groins, the cen tre of g-ravity of the ground-plan is calculated therefor; where the ground plan is a reg-ular polygon, this will be the centre point. If large apart ments are to be arched, groups of groined vaults are frequently adopted, the apartments being divided into sections as nearly square as possible by means of pillars and transverse arches, as shown in Figure 14.
Lierne vaulting shown in Fig-ure tit is not a pure groined vault, but a " Herne," where the surfaces are divided not only by the diag onal ribs, but also by intermediate ribs, into numerous sections; so that the ground-plan is in the form of a star. This species of vaulting, which is very rich in effect, is often employed in the Gothic style; the one repre sented, which is an example of very bold vaulting, is taken from the l',Iarienburg- Castle, a Gothic structure in West Prussia. The Figure shows the vaulting of the Grand Hall (Routers), which has a slender supporting pillar in the centre.
In regard to the distribution of pressure in ?Joined vaults, it may be remarked that the enclosing walls, even where there is a rise toward the vertex, receive very little of it, but more is thrown on the corners; on this account the latter are often strengthened by pillars, the walls being of moderate thickness. In reference to the thickness of groincd vaults, it is stated that for spans of about 16y.,, feet the ciiagonal ribs need be only one brick wide and thick, and the sectroids only one-half brick.
The Corea' may likewise be considered as arising from the inter penetration of two or more cylindrical or barrel vaults, except that here the sections of the cylinder have another position. They present, not the span-opening, but •the abutment sides, to the enclosing- wall; and thus arise penetrations which appear as coves on the inner surface of the vault. These vaults, as they begin only above the vertex of the opening con tained in the enclosing walls, and thus require great height, are seldom employed.