1450
THEORY AND PRACTICE OF ENGINEERING.
Book IT.
a large block of stone or a central key, to keep them in their place, and to lock themtogether, which would form a very solid vault, and is the principle of keyed ribs.
When four arches raised on the sides of a square, as in the compartments of a cloister,traverse each other, and unite over the centre, they are called
The Voute d Arete and Are de Cloitre , and are composed of triangular portions of a semicir-cular vault: in the first, each of these parts only rests on two of their angles, as A, while in thatof the arc de cloitre each triangular part, EDC, has for its base one of the sides, which rest
Fig. 2567.
Fig. 2571. voussoir at b.
Fig. 2572. first voussoir.
ARC DE CLOITRE ON A SQUARE PLAN.
E /A
Fig. 2573.
Fig. 2574.
Fig. 2569. voute d’arete. Fig 2570. arc de cloitre.
KEYSTONE.
on the wall throughout its whole extent: each part of the vault in the arc dc cloitre isformed by portions cut from two intersecting semicircular vaults of the correspondingvoute d’arete, that is to say, agree in figure and dimension.
Arc de Cloitre , on a square plan, having its primitive centre a semicircle, shows thejoints of the several voussoirs: the drawn lines indicate the intrados, and the dotted theextrados.
The rows of voussoirs inscribed on each other form hollow squares, subdivided by joints .perpendicular to their sides: this projection serves to find the base of the prisms inwhich each voussoir is contained. The section indicates the form of the several stones.
The four examples of development at the sides show the intrados of the voussoirs formingthe re-entering angles which characterise this kind of vault; the voussoirs are indicated onthe plan and section by the several letters, A, B, C, D, and E. The upper figure in perspec-tive is the voussoir marked B, the other is that marked A.
Fault of Arc de Cloitre with an Octangular Plan. — The general setting out is the same as inthe previous figure. The primitive centre is a semicircle, as seen on the section, which when