Arch (structure)

“ An arch consists of a series of wedge shaped blocks, known as voussoirs, arranged in a curve, and so locking one another together that unless the abutments from which the arch springs give way, it will not only carry itself, but sustain a heavy load. ”

“ Arches are constructions built of wedge-shaped blocks, which by reason of their shape give support one to another, and to the super-imposed weight, the resulting load being transmitted through the blocks to the abutments upon which the ends of the arch rest. An arch should be composed of such materials Arches.and designed of such dimensions as to enable it to retain its proper shape and resist the crushing strain imposed upon it. ”

“ There is not the smallest necessity, because the arch is pointed, that the aperture should be so. The work of the arch is to sustain the building above; when this is once done securely, the pointed head of it may be filled in any way we choose. ”

“ The essential quality of the arch, it is elasticity. The wider it is, the broader the space which it must cross is, and the more necessary it is that it is flexible. The manufacturers of the Middle Ages followed this principle perfectly by multiplying the joints in their archs, by composing them of equal archstones, always extradossés carefully. ”

“ It is rather a heavy weight to bear, but a solid arch spans over our heads. The great Architect has built it of the best materials; and never could man have given it so wide a stretch. What are the finest arches of bridges and the arcades of cathedrals, compared with this far reaching vault, with a radius of three leagues, beneath which a wide and tempest-tossed ocean may flow at its ease? ”

“ Most of the arches are built with alternate voussoirs of brick and stone, but beyond the outside line of the brick and stone arch there is invariably a line of very thin bricks laid all round the arch, delicately defining without pretending to strengthen the main arch, just as a label does with us. ”

“ It is independent enough not to care about the holes cut in it, and does not subside into them like sand. But the theory of arches does not presume on any such condition of things; it allows itself only the shell of the arch proper; the vertebræ, carrying their marrow of resistance; and, above this shell, it assumes the wall to be in a state of flux, bearing down on the arch, like water or sand, with its whole weight. And farther, the problem which is to be solved by the arch builder is not merely to carry this weight, but to carry it with the least thickness of shell. ”

“ DISCHARGING ARCH, in architecture, an arch built over a lintel or architrave to take off the superincumbent weight. The earliest example is found in the Great Pyramid, over the lintels of the entrance passage to the tomb: it consisted of two stones only, resting one against the other. ”

“ Norman architecture is in the use of the pointed form of arch, yet in the study of the early buildings of this date it is curious to notice how evenly the balance is held between the pointed and the round arch, and how at one time it was quite an open question whether the Gothic style would be distinguished by a round or a pointed arch. ”

“ The types which I found in nature or in practice are of the stalactitic, dome, and arch,—the horseshoe arch, the tracery on the wall, the diversified colouring of that tracery, the half-globe dome upon the cube; and these, in fact, are the modifications that the architecture of Judæa received, and by which it has been converted into the Moorish.
On the material the system of architecture depended, and it is wholly different from the classic. The great styles of antiquity depended, not on the adhesion of the stones, but their form and weight, and by science alone they obtained arches. ”

“ The extra height of the arch is unnecessary as an opening, the arch being required for its strength only, not for its elevation. There is, therefore, no reason why it should not be barred across by a horizontal lintel, into which the valves may be fitted, and the triangular or semicircular arched space above the lintel may then be permanently closed, as we choose, either with bars, or glass, or stone. ”

“ Sir, so long as public approval be won, what matter for the arch? But that they are two, take this as sufficient explication——that they are too tall for doorways, too narrow for gateways; too light without, too dark within; too plain to be ornamental, and withal too fantastic to be useful. And if this be not enough, you are to note further that, were it all one arch, it must needs cut short one of those shafts which grace the Quadrangle on all sides——and that were a monstrous and unheard-of thing, in good sooth, look you. ”

“ Similarly the towers of churches and cathedrals, which are built on arches, will give away quite suddenly after standing to all appearance quite firm for hundreds of years. There is an architect's maxim which runs, "The arch never sleeps." That means that the arches on which the great weight of a church or cathedral tower rests are always in a state of strain; they are always, as it were, imperceptibly quivering; and they are always liable, if the strain on them should be increased in the slightest degree, to give way, or to resettle the weight on their shoulders in some way. ”

“ Arches.—The semicircular is the characteristic form of the Norman arch, but there are few early examples in which the pointed arch was used, supported by massive piers; they are not likely to be mistaken for those of the next style. In the transition the pointed arch is very frequently used. Sometimes the arch is brought in a little at the impost, when it is called a horse-shoe arch; and sometimes the spring of the arch is above the impost, and is carried down by straight lines. ”

“ Arches cannot be used beyond a limited span, because the strain upon the materials becomes too great for their powers of resistance to withstand. Each of the stones in an arch is squeezed by intense pressure, and there is a limit beyond which even the stoutest stones cannot be relied upon. ”

“ The continuance of these arches depends upon the resistance of the stones forming them to a crushing force. Each stone of an arch is subjected to a vast pressure, but stone is a material capable of resisting such pressure, and the arch remains. ”

“ The abacus of the capital is invariably square in plan, and has its upper edge (except in a few of the latest examples) also square in section.
In the later buildings of the Period, foliage, exhibiting considerable freedom of design, is occasionally to be seen.
The Pointed Arch first made its appearance in the Transitional Period; in the earlier buildings it is used in the Arches of Construction only, or those constituting the framework of the building, such as the Pier-arches and the Arches of the Vaulting, and of the Crossing ”

“ A true arch is formed of a series of wedge-like stones or of bricks, supporting each other, and all bound firmly together by the pressure of the centre one upon them, which latter is therefore distinguished by the name of keystone. ”

“ Some critics see nothing more than the unequal size of these arcades, when the real point is to find the architectural centre, whence the composition radiates, majestic and imperious. The topmost arches and their crowning dignify the whole structure with a completeness akin to that which is given to a long range of columns by a fine entablature and cornice. ”

“ The proportions of the internal elevation are such that, if the entire height of the wall be divided into nine parts, four go to the main arcade, two to the triforium or gallery, and three to the clerestory (Fig. 253) .
Fig. 253.—Sectional view of Nave, St. Alban’s.
The arches of each are of three orders, and are, for the most part, without shafts; the section of the jamb and arch being the same, severed only by a simple{102} impost. A broad pilaster buttress runs up the face of each pier from floor to ceiling. ”

“ The column c b, being charged with an equal weight, [on each side] will be most durable, and the other two outward columns require on the part outside of their centre as much pressure as there is inside of their centre, that is, from the centre of the column, towards the middle of the arch.
Arches which depend on chains for their support will not be very durable.
THAT ARCH WILL BE OF LONGER DURATION WHICH HAS A GOOD ABUTMENT OPPOSED TO ITS THRUST. The arch itself tends to fall. ”

“ The whole tendency, too, of the onward movement of the art was towards increased height; and, while walls and pillars might avail themselves to the full of this upward striving, it was hard that the arch—the very essence of the style—should be condemned to unalterable stuntiness. Proportion evidently claimed that the arch should have its fair share in the increasing height of the buildings, yet the inexorable semicircle said, “Nay, my proportions are fixed. You may lengthen your straight lines as you please; but by no law of science can my height exceed one-half of my width.” ”

“ What, then, will be the next easiest method of giving interest to the fillet?
§ XIII. Simply to make the incisions square instead of sharp, and to leave equal intervals of the square edge between them. Fig. LVIII. is one of the curved pieces of arch armor, with its edge thus treated; one side only being done at the bottom, to show the simplicity and ease of the work. This ornament gives force and interest to the edge of the arch, without in the least diminishing its quietness. Nothing was ever, nor could be ever invented, fitter for its purpose, or more easily cut. ”

“ Some idea of the 'Triumphal Arch' is conveyed to our mind when we learn that it was drawn on ninety-two separate blocks of wood, and that when properly joined it is ten and a half feet high and nine and a half feet wide! ”

“ It is in some degree considered as a characteristic of the Anglo-Saxon and Norman styles. The stilted arch is chiefly found in conjunction with the semicircular arch in the construction of Norman vaulting over a space in plan that of a parallelogram. The segmental arch we meet with in almost all the styles, used as an arch of construction, and for doorway and window arches; whilst the form of the horse-shoe arch seems, in many instances, to have been occasioned by the settlement and inclination of the piers from which it springs. ”

“ A comparison, for example, of the plans of the Hypostyle Hall at Karnak (Fig. 11, h) and of the Basilica of Constantine (Fig. 58) shows at once a radical difference in constructive principle between the two edifices, and hence a difference of style.
STRUCTURAL PRINCIPLES. All architecture is based on one or more of three fundamental structural principles; that of the lintel, of the arch or vault, and of the truss. The principle of the lintel is that of resistance to transverse strains, and appears in all construction in which a cross-piece or beam rests on two or more vertical supports. ”

“ Blocks of compressed rock beneath a relatively flat ceiling tend to be dislodged also by expansion due to release of pent-up pressure, until a strong self-supporting arch is formed. Release of pent-up pressure in rock walls may help also in initiating the formation of alcoves or caves in cliff faces. Man, including the ancient Greeks, Romans, Egyptians, and others, has long made use of arches in building bridges, aqueducts, temples, cathedrals, and other enduring edifices. ”

“ It was at first used for the main arch only of the greater vault. The same reason soon led to its introduction wherever great weight was to be carried, as under towers, etc.; but for all small arches the semicircle was long retained. I have alluded to the very beautiful theory that it was introduced for the side arches of oblong groins, simply as a means of obtaining arches of equal height with only half the span with those of the main vault. ”

“ The problem was ultimately solved by the introduction of the pointed arch for the transverse and wall ribs—the pointed arch had long been known and employed, on account of its much greater strength and of the less thrust it exerted on the walls. When employed for the ribs of a vault, however narrow the span might be, by adopting a pointed arch, its summit could be made to range in height with the diagonal rib ”

“ But the friction of the vaulting stones against one another prevents this instability from being a practical inconvenience; and makes an equilibrated arch to be an arch strong for practical purposes. The Theory of Arches is a portion of Mechanics which has been much cultivated, and which has led to conclusions of practical use, as well as of theoretical beauty. ”

“ We must, however, do the late builders the justice to note that, in one case, the habit grew out of a feeling of proportion, more refined than that of earlier workmen. It shows itself first in the bases of divided pillars, or arch mouldings, whose smaller shafts had originally bases formed by the continued base of the central, or other larger, columns with which they were grouped; but it being felt, when the eye of the architect became fastidious, that the dimension of moulding which was right for the base of a large shaft, was wrong for that of a small one, each shaft had an independent base ”

“ It may excite surprise that what appears to be so small a difference as that which exists between a beam, a round arch, or a pointed arch, should be employed in order to distinguish three of the four great divisions. ”

“ The Arches vary in form from a very blunt to a very sharp point, but they are generally acutely pointed, and are often richly moulded, as in Westminster Abbey. The mouldings, however, are the safest guide to the style, as the form of the pointed arch largely depends on convenience. As a rule, they are generally more acutely pointed in the cathedrals and large churches, whilst they are broader in small churches. ”