صور الصفحة

one-eighth of an inch deep, first by the edge of the level, on the face of the brick, then, by the edge of the square, on the bed of the brick, in order to enter the brick-axe, and to keep the brick from spalting. The saw is also used for cutting the soffit through its breadth, in the direction of the tapering lines drawn upon the face and back edge of the brick, and also for cutting (he false joints of headers and stretehers; Fig. 24g.2i- TI'C brick-axe, Fig. 249, for axing off the soffits of bricks to the saw cuttings, and the sides to the lines drawn by the scribes. The bricks being always rubbed smooth after axing, the more truly they are axed, the less labour will be required in rubbing them; 25. The templet, used for taking the length of the stretcher and width of the header; 26. The chopping-block, for reducing bricks to their intended size and form, by axing them. It is a piece of rough wood, six or eight inches square, supported on two fourteeninch brick piers; but it varies in size according to the number of men working at it; 27. The floatstone, used for rubbing curved work smooth, such as the cylindrical backs and spherical heads of niches, to take out the axe marks. It is previously brought into a form the reverse of the surface to which it is applied.

In the raising of brick walls, it is of great importance to secure a good foundation. Trenches are dug for foundations, and the ground is tried with a crowbar or rammer, to ascertain its soundness. If it appear to shake, it must be bored with a well-sinker's tool, to ascertain whether the shaking be local or general. If the soil be firm, the looser parts, if not very deep, are dug up, until the solid bed is got at. If the ground be not very loose, it may be made good by ramming into it large stones, closely packed together; but if the ground be very bad, it must be piled and planked, and in such cases, concrete is of very great service. In rising ground, the foundation must be made to rise in a scries of steps. When the ground is loose in places over which it is intended to make windows, doors, &c., while the ground at the sides on which the piers are to stand is firm, it is usual to turn inverted arches over such intended openings, Fig. 250. This is a necessary precaution

[graphic][merged small]

piers ought to be as uniform as possible, for, although the bottom of the trench may be very firm, yet, if it vary in firmness, the piers will settle more in one place than in another, and thus occasion a vertical fracture in the superstructure. Should the solid parts of the trench be under the intended openings, and the softer parts where piers are to be built, on firm ground, arches, not inverted, must be suspended between them; in which case, attention must be paid to the insisting pier, whether it will cover the arch or not; for if the middle of the pier rest over the middle of the summit of the arch, the narrower the pier, the greater should be the curvature of the arch at its apex. When suspended arches are used, the intrados ought to be clear, that the arch may have its full effect. Here, also, the ground on which the piers are erected must be of equal firmness, lest the building be injured by unequal settling, which is much more mischievous than where the ground, from being uniformly soft, allows the piers to descend equally, in which case the building is seldom or never damaged.

In ramming foundations, the stones, previously chopped or hammered, should be laid of a breadt'n proportionate to the weight intended to rest on them, and rammed closely together with a heavy rammer. The lower bed of stones may in general project about a foot on each side of the wall: on this another course may be laid, so as to bring the upper bed of stone upon a general level with that of the trench, projecting about eight inches on cither side of the wall, or receding four inches on each side within the lower course. The joints of every upper course iuust fall as nearly as possible on the middle of the stones in the course immediately beneath it; a rule to be strictly attended to in every kind of walling; for in all the modes of laying stones or bricks, the object is to obtain the greatest lap one upon the other.

In slacking the lime for preparing the mortar for the wall, no more water should be used than is barely sufficient to reduce it to powder, and it should be covered with a layer of sand to exclnde the air. It is best to slack the lime in small quantities, about a bushel at a time. When the mortar is about to be used, it should be beaten three or four times, and turned over with the beater, so as to incorporate the lime and sand, a little water being added. In hot and dry weather the mortar may be made much softer than in winter. In dry weather, and for fine work, the bricks should be wetted or dipped in water as they are laid; a precaution not required in damp weather. This wetting causes the bricks to adhere to the mortar, which they will not do if laid dry and covered with sand or dust, in which case they may often be removed without any mortar adhering to them. In working up the wall, not more than four or five feet of any part should be built at a time; for, as all walls shrink directly after building, the part which is first raised will settle before the adjacent part is brought up to it, and the shrinking of the latter will cause the two parts to separate. Unless it be for the accommodation of the carpenter, no part

[merged small][graphic][merged small][graphic]

Fig. 253.

Fig. 252.

traduced into England about the reign of William

and Mary, consists in placing a header and a streteher alternately in the same course. The effect is more pleasing than the former, but this mode does not produce so strong a wall. The face of an upright wall in English bond is shown in Fig. 253, and that of Flemish bond in **■ "4- Fig. 251.

Fig. 255 is English bond in a nine-inch walling. Mr. Nicholson remarks that, as the length of a brick is nine inches, and its breadth 4£, it is usual, to prevent two vertical F'3'2'5' joints from running over

each other, at the end of the first streteher from the corner, to place the return corner streteher, which becomes a header in the face that the streteher is in below, and occupies half its length; a quarter brick is placed on inside, so that the two together extend fif inches, leaving a lap of 2£ inches for the next header, which lies with its middle upon the middle of the header below, and forms a continuation of the

[ocr errors]
[ocr errors]

bond. The three-quarter bat thus introduced is called a closer. A similar effect might be obtained by introducing a three-quarter bat at the corner of the stretehing course, and then the corner header being laid over it, a lap of 2£ inches will be left at the end of the stretehers below for the next header, which being laid, the joint below the stretehers will coincide with its middle, and thus form the bond.

In a fourteen-inch, or brick-and-a-half wall, Fig. 256, the stretehingcourse upon one side is laid so that the middle of the breadth of the bricks upon the opposite side falls alternately upon the middle of the stretehers and upon the joints between the stretehers.

In a two-brick wall, Fig. 257, every alternate header in the headingcourse is only half a brick thick on both sides, which breaks the joints in the core of the wall.

In a two-and-a-half brick wall, Fig. 258, the bricks are laid as shown in Fig. 259.


Flemish bond for a nine-inch wall is shown in Fig. 260, where two stretehers lie between two headers; the length of the headers and the breadth of the stretehers extending the whole thickness of the wall.

In brick-and-a-half Flemish bond, one side is laid as in Fig. 260, and the opposite side with a half-header opposite to the middle of the streteher, and the middle of the streteher opposite the middle of the end of the header.

The adoption of Flemish bond leads to the frequent splitting of walls; and to prevent it, laths, or slips ot hoop-iron, are sometimes laid in the horizontal joints between the two courses. Others have laid diagonal courses of bricks at certain heights from each other. Attempts have also been made to unite complete bond with Flemish facings, for the sake of the improved appearance which the latter gives. In Figs. 261, 262, 263, 264, the interior bricks are represented as disposed so as to unite the two methods,

[merged small][table][ocr errors][ocr errors][ocr errors][ocr errors]

the adjustment of the bricks in one course must depend upon the course beneath, which must be recollected by the bricklayer after he has covered the course with mortar. Even should he keep his attention thus alive, the work is not so strong as English bond, which, if executed with the same attention and neatness as is required by the Flemish, would be equally handsome in appearance.

Mr. Nicholson gives the following rules for forming English bond:—1. Each course is to be formed of headers and stretehers alternately; 2. Every brick in the same course must be laid in the same direction; but in no instance is a brick to be placed with its whole length alongside of another; but to be so situated that the end of one may reach to the middle of the others which lie contiguous to it, excepting the outside of the stretehing-course, where three-quarter bricks necessarily occur at the ends, to prevent a continued upright joint in the face-work; 3. A wall which crosses at a right angle with another will have all the bricks of the same level course in the same parallel direction, which completely bonds the angles, as shown by some of the preceding Figures.

In building a wall, bricks should incline slightly towards the middle of the wall, that one-half of the wall may act as a shore to the other. It was formerly the practice to build pieces of timber, called bond timbers, into the wall, running through its whole length, in order to add to its strength. This method of building walls is objectionable, because if the timber should decay, the wall may fail before any one is aware of the cause of failure. This method of bonding is now almost entirely superseded by the hoop-iron bond, which consists in laying hoop-iron flatwise between the courses. The iron should be slightly rusted, by which its adhesion to the mortar is greatly increased.

In winter it is important to preserve the unfinished wall as much as possible from the alternate effects of rain and frost, the one penetrating into the materials, and the other converting the water into ice, which by its expansion bursts, and crumbles the materials. The unfinished wall must therefore be covered with straw, or with a weather boarding in the form of a stone coping, with a body of straw under the wood.

Brick-work is measured by the rod. A rod of brick-work taken from the original standard of 16£ feet square, contained in the superficial rod 272£ square feet, but as the quarter was found troublesome in caleulation, 272 superficial feet came to be the standard for brick-work. The standard thickness of a brick wall is oue and a half brick in length, so that if 272 square feet be multiplied by 13£ inches,


the result is 306 cubic feet in the rod. A rod of standard brick-work with mortar, will require 4,500 bricks on an average, allowing for wiste, this number depending on the closeness of the joints, and the size of the bricks. The mortar in a rod of brickwork will require 1^ cwt. of chalk lime, or 1 cwt. of stone lime, and 2i loads of sand with stone lime or 2 loads with chalk lime. The weight of a rod of brick containing 4,500 stock bricks, 27 bushels of chalk lime, and 3 single loads of drift sand, is about 13 tons.

The bricklayer's labourer is paid at the rate of two-thirds of the bricklayer's wages per day. One labourer is sufficient for a bricklayer when on the ground, but as the work advances in height, more may be required. In common walling, where there are few or no interruptions by apertures or recesses, the bricklayer will lay 1,000 bricks in one day, or complete a rod in about 4£ days.

There is a method of constructing a wall with a row of posts or quarters 3 feet apart, the intervals of which are filled up with brick-work. This is called bricknogging. It is seldom more than the width of a brick in thickness, and should not be used where thickness can be obtained for a nine-inch wall.

After a wall is built, the joints of the bricks on the face are sometimes filled up with mortar, so as to present a regular and neat appearance. This is called pointing, and is of two kinds, in both of which the mortar in the joints is well raked out, and filled up again with blue mortar; but in one kind, called flat-joint pointing, the courses are simply marked with the edge of a trowel. If in addition to this, plaster be inserted in the joints with a regular projection, and neatly pared to a parallel breadth, this is called tuck-pointing or tuck-joint pointing.

Groined arches are sometimes made of brick. A groin is the angular curve formed by the intersection of two semi-cylinders or arches. They are raised on centres formed of carpentry work. The turning of a simple arch on a centre requires only care to keep the courses as close as possible, and to avoid the use of much mortar on the inner part of the joints. The difficulty of executing a brick groin arises from the peculiar mode of making proper bond at the intersection of the two circles as they gradually rise to the crown, where they form an exact point. In the meeting or intersecting of these angles, the inner rib should be perfectly straight and perpendicular to a diagonal line drawn on the plan. After the centres are set, the application of the brick to the angle will show in what direction it is to be cut. The sides are turned as in common cylindric vaults.

A variety of ornamental brick cornices may be formed by cutting and changing the position of the bricks employed. Others may be formed by chamfering only.

Niches in brick-work form the most difficult part of the bricklayer's art. The difficulty arises from the thinness to which the brick must be reduced at the inner circle, as they cannot extend beyond the thickness of oue brick at the crown or top, it being


usual as well as neatest to make all the courses standing.

The chief authority in this article has been Nicholson's New Practical Builder, London, 1823. One of the earliest treatises on Bricklaying is contained in the "Mechanick's Exereises on the doctrine of Handyworks," by Joseph Hoxon, third Edition, London, 1703. The Author in his Preface seems to think an apology necessary for writing on snch humble subjects as "Bricklayery;" but he says:— "I see no more reason why the sordidness of some workmen should be the cause of contempt upon manual operations, than that the excellent invention of a mill should be despised because a blind horse draws in it."

BRIDGE. An elevated construction upon or over a depression, and between depressed points, probably derived from the word ridg?, with the prefix be. Professor Hosking defines a bridge as "a constructed platform, supported at intervals or at remote points, for the purpose of a road-way over a strait, an inlet or arm of the sea, a river, or other stream of water, a canal, a valley, or other depression, and over another road; distinguished from a causeway, or embanked or other continuously-supported road-way, and from a raft, by being so borne at intervals or at remote points."' Aqueducts, for conveying streams of water or canals, and viaducts, for carrying roads or railways, upon the same, or nearly the same, level, over depressions, are practically considered as bridges.

One of the most important requisites in a bridge is permanence. It ought to form a portion of the solid road which it connects, so as to combine comparative ease of approach with convenience of passage and agreeableness of design. The whole depression or valley must practically be obliterated in its effect upon the road, by means of the bridge passing from one summit to the other, so that the ordinary traffic may be carried on without interruption. The bridge must also afford facility of passage under it, not only for the stream, but also for the commeree of men and merehandise which are borne along upon the waters.

But a bridge is not limited to one particular form, size, proportion, material, mode of construction, arrangement, or design, but is such as cireumstances require it to be. Where a stream or body of water occurs in the line of a great public road, so as to interrupt its continuity, some kind of bridge is necessary. In a river, estuary, strait, or arm of the sea, where the banks are wide and low, and where the navigation for vessels with lofty rigging is to be kept free, an ordinary bridge may be impossible, and a floating bridge, such as a passage-raft, or punt, may be all that can be allowed. For example, the great mail-road from the metropolis, through Bristol, into South Wales, is intereepted by the Severn: the river is wide; its banks are low; the water is sufficient for marine navigation, and the trade of the country

(I) " The Theory, Practice, and Arehitecture of Bridges of Stone, Iron, Timber, and Wire; with Examples on the principle of Suspension: IUustrated by 138 Engravings, and 92 Wood-cuts." Weale: London. 1843.

requires that its course should remain open for that purpose. Hence, the erection of a bridge is prohibited. But where the banks are high, and the channel comparatively narrow, a bridge may be thrown over, as in the case of the Wear, at Bishop's Wearmouth, by Sunderland. So, also, the Straits of the Menai are passed over by the great Holyhead road, without impeding the passage of ships through the straits.

In treating of so extensive and complicated a subject as that of bridges, the literature of which forms a library in itself, it will be desirable to divide it into sections, by bringing together, first, a few notes on the History of Bridges, chiefly of stone; secondly, some details respecting the Theory of Bridges; thirdly, the Practice of Bridge-building; fourthly, Timber-bridges; fifthly, Suspension-bridges; and lastly, Iron, Girder, and Tubular-bridges.

Section I.—Historical Notice Of Bridges.

The art of bridge-building, like all other useful arts, was of slow growth, and has shared in all the varied changes of man's social position at different periods of his history. In a rude state of society, the most obvious and simple bridge is a tree thrown across a stream; or, if the breadth of the stream be too great to be spanned by a single tree, a tree on each side of the stream bent down, and the branches twisted together in the middle. Mungo Park observed this method on the rivers in the interior of Africa. Another step in advance is to stretch across a river a number of ropes, made of rushes or leathern thongs, secured on the opposite banks between trees and posts, and connected and covered, so as to form a slight bridge. This method is practised in some of the mountainous districts of South America. The ropes are formed of thongs of ox-hide, consisting of several strands, about six or eight inches in thickness, and across these, in a transverse direction, sticks are laid, and these are covered with a flooring of branches of trees. In other cases, an ox-hide rope is extended from one side of the river to the other, and is secured to each bank by means of strong posts. On one side is a kind of wheel, or winch, to straighten or slacken the ro|'e, from which hangs, by a clue at each end, a kind of leathern hammock, capable of holding a man. A rope fastened to either clue, and extended to each side of the river, is used for drawing the hammock to the side intended. A push at its first setting-off sends it quickly to the other side. Mules are carried over in this way.

Another mode of bridge-building is to construct piers of stone, at a short distance from each other, to be spanned by single stones or slabs, or by beams of timber. When this kind of bridge is used for shallow streams, and is composed of rough stones, without mortar, the operation is simple; but in deep and rapid streams, the construction of piers of hewn stone indicates a considerable advance in the useful arts, because a proper foundation for each pier is required. The bridge over the Euphrates at Babylon was thus formed, and this method of construction is common in different parts of China.

In this singularly interesting country, also, the arch—that grand feature in a bridge—has been in use for many ages; but the Chinese—in many cases, at least—do not seem to have constructed arched bridges of sufficient strength to bear carriages. The arch, however, covers the gateways in the great wall; and Kircher speaks of stone bridges in China, three and four miles long, and of an arch of the incredible span of six hundred feet. In Egypt and India, the arch does not seem to have been known, or applied to the construction of a bridge; for although brick arches are said to have been found buried in the tombs of Thebes, yet the ancient Egyptians never built a permanent bridge across the Nile. There is no trace of the arch in the ancient works of Persia or Phoenicia; and even the Greeks, who created a school of architecture and sculpture, have a very doubtful claim to the knowledge of the arch. When Pericles adorned the city of Athens with splendid edifices, a stone bridge was not constructed over the small river Cephisus, although upon the most frequented road to that city. It is to the Romans that the western world is indebted for this useful invention. There is great uncertainty as to the time when the Romans first used the arch. If the cloaca of Rome were constructed in the time of the elder Tarquin, the use of arches must have been then well known. Some writers suppose that the Romans derived their knowledge of the arch from the Tuscans, a colony of Dorians, and hence intimately connected with Greece. Some of the ancient Roman bridges still exist. (See Fig. 265.) One of the most magnilicent was built by Augustus, near Narni, on the


Fig. 205. PONS Sf-aatorius.
(Now call'-d Sancta Maria.)

road from Rome to Loretto. It consisted of four arches, the first of 75 feet span, and 102 feet height; the spans of the other arches were 135, lit, and 142 feet, respectively. In the provinces, the Komans built many magnificent bridges. The bridge of Mcrida, on the river Guadiana, is said to have been 1,300 paces long, with 64 arches. But, perhaps, the most magnificent of all the Roman bridges, and one of the noblest monuments of antiquity, is the bridge of Aleantara, on the Tagus, consisting of 6 arches: the whole length is 670 Spanish feet, and the

height, from the bed of the river to the roadway, is 205 feet.

From the destruction of the Roman empire to the establishment of modern Europe, there are no bridges of importance, except those fine works by the Moors in Spain, particularly the bridge of Cordova, over the Guadalquiver. When the arts began to revive in Europe, they were chiefly directed to religious structures. There was little security for travellers, especially in passing rivers, where they were exposed to violent exactions by banditti and robber knights. To put a stop to these disorders, sundry persons formed themselves into fraternities, which became a religious order, under the title of the Brethren of the Bridge. The object of this institution was to build bridges, establish ferry-boats, and receive travellers into hospitals on the shores of rivers. The first establishment was upon the Durance, at a dangerous spot named Maupat; but, in consequence of the accommodation arising from this establishment, it acquired the name of Bonpas. It is related that St. Benczet, who proposed and directed the building of the bridge of Avignon, was a shepherd; and that, at the age of twelve, he was supcrnaturally commanded to quit his flock, and undertake this enterprise; that he arrived at Avignon at the time when the bishop was preaching to fortify the minds of the people against an eclipse of the sun, which was to happen t he same day. Benezet raised Iub voice in the church, and said that he was come to build a bridge. His proposal was accepted by the people with applause, but rejected by the magistrates and some others. As it was at that time an act of piety to build a bridge, and Avignon was then a popular republic, the people prevailed; and every one contributed to the good work, some by money, and some by labour, all under the direction of Benczet, aided by the Brethren. Upon the third pier was erected a chapel to St. Nicholas, protector of those who navigate rivers. This was done in 1184, after the death of Benezet, who established a conventual house and a hospital, leaving the Brethren to continue the work of the bridge. This bridge was commenced in 1176, and completed in 1188. It was composed of 18 arches. In 1385, during the contentions of the popes, some of its arches were destroyed: three others fell in 1602, from the neglect of repairing a fallen arch. In 1670, the frost was so great that the Rhone, for several weeks, bore the heaviest carriages: when the thaw followed, the piers were destroyed, except the third, which bore the chapel. The fine bridges of Lyons, of 20 arches, and St. Esprit, of 19, were erected by the surviving Brethren of the Bridge.

According to Perronet, an arch of 150 French feet (equal to 160 English feet) span was erected at Verona, in 1354; and, in 1454, one of 183.8 English feet span, and 70.6 feet of rise from the springing, at Vielle Brionde, upon the river Allier, in France. There are also many fine bridges in Italy. The finest in Venice is the Rialto, of 98£ feet span, aud 23 feet rise: it was designed bv Michael Angelo, and

« السابقةمتابعة »