Part 67

Piers, the walls built for the support of the arches, and from which they spring as their bases. They should be built of large blocks of stone, solid throughout, and cramped together with iron, which will make the whole as one solid stone. Their faces or ends, from the base up to high-water-mark, should project sharp out with a salient angle, to divide the stream: or, perhaps the bottom of the pier should be built flat or square up to about half the height of low-water-mark, to allow a lodgement against it for the sand and mud, to go over the foundation; lest, by being kept bare, the water should in time undermine, and so ruin or injure it. The best form of the projection for dividing the stream, is the triangle; and the longer it is, or the more acute the salient angle, the better it will divide it, and the less will the force of the water be against the pier; but it may be sufficient to make that angle a right one, as it will make the work stronger; and in that case the perpendicular projection will be equal to half the breadth or thickness of the pier. In rivers, on which large heavy craft navigate and pass the arches, it may, perhaps, be better to make the ends semicircular: for, although it does not divide the water so well as the triangle, it will both better turn off and bear the shock of the craft.

The thickness of the piers should be such as will make them of weight or strength sufficient to support their interjacent arch independent of any other arches; and then, if the middle of the pier be run up to its full height, the centering may be struck to be used in another arch before the hanches are filled up. The whole theory of the piers may be seen in the third section of Professor Hutton’s Principles of Bridges.

They should be made with a broad bottom on the foundation, and gradually diminishing in thickness by off-sets up to low-water-mark.

Piles, are timbers driven into the bed of the river for various purposes, and are either round, square, or flat like planks. They may be of any wood which will not rot under water; but oak and fir are mostly used, especially the latter, on account of its length, straightness, and cheapness. They are shod with a pointed iron at the bottom, the better to penetrate into the ground, and are bound with a strong iron band or ring at top, to prevent them from being split by the violent strokes of the ram by which they are driven down.

Piles are either used to build the foundations on, or they are driven about the pier as a border of defence, or to support the centres on; and in this case, when the centreing is removed, they must either be drawn up, or sawed off very low under water; but it is better to saw them off and leave them sticking in the bottom, lest the drawing of them out should loosen the ground about the foundation of the pier. Those to build on, are either such as are cut off by the bottom of the water, or rather a few feet within the bed of the river; or else such as are cut off at low-water mark, and then they are called stilts. Those to form borders of defence, are rows driven in close by the frame of a foundation, to keep it firm, or else they are to form a case or jettée about the stilts, to keep the stones within it, that are thrown in to fill it up: in this case, the piles are grooved, driven at a little distance from each other, and plank-piles let into the grooves between them, and driven down also, till the whole space is surrounded. Besides using this for stilts, it is sometimes necessary to surround a stone pier with a sterling, or jettée, and fill it up with stones to secure an injured pier from being still more damaged, and the whole bridge ruined. The piles to support the centres may also serve as a border of piling to secure the foundation, cutting them off low enough after the centre is removed.

Pile-driver, an engine for driving down the piles. It consists of a large ram or iron sliding perpendicularly down between two guide posts; which being lifted up to the top of them, and there let fall from a great height, comes down upon the top of the pile with a violent blow. It is worked either with men or horses, and either with or without wheel-work. The bridge on Schuylkill, Philadelphia, is a master-piece of workmanship; and the new bridge at Trenton, over the Delaware, is equally bold and ingenious in its plan--in the latter the floor is suspended from the voussoirs of the arches, by stirrups of iron.

Pitch, of an arch, the perpendicular height from the spring or impost to the key stone.

Plan, of any part, as of the foundations, or piers, or superstructure, is the orthographic projection of it on a plane parallel to the horizon.

Push, of an arch. See DRIFT.

Salient angle, of a pier, the projection of the end against the stream, to divide itself. The right-lined angle best divides the stream, and the more acute, the better for that purpose; but the right angle is generally used, as making the best masonry. A semicircular end, though it does not divide the stream so well, is sometimes better in large navigable rivers, as it carries the craft the better off, or bears their shocks the better.

Shoot, of an arch. See DRIFT.

Springers, are the first or lowest stones of an arch, being those at its feet, and bearing immediately on the impost.

Sterlings, or Jettées, a kind of case made about a pier of stilts, &c. to secure it, and is particularly described under the next word, Stilts.

Stilts, a set of piles driven into the space intended for the pier, whose tops being sawed level off, above low-water mark, the pier is then raised on them. This method was formerly used when the bottom of the river could not be laid dry; and these stilts were surrounded, at a few feet distance, by a row of piles and planks, &c. close to them like a coffer-dam, and called a sterling, or jettée; after which loose stones, &c. are thrown or poured down into the space, till it is filled up to the top, by that means forming a kind of pier of rubble of loose work, and which is kept together by the sides or sterlings: this is then paved level at the top, and the arches turned upon it. This method was formerly much used, most of the large old bridges in England being erected that way, such as London bridge, Newcastle bridge, Rochester bridge, &c. But the inconveniences attending it are so great, that it is now quite disused; for, because of the loose composition of the piers, they must be made very large or broad, or else the arch must push them over, and rush down as soon as the centre was drawn; which great breadth of piers and sterlings so much contracts the passage of the water, as not only very much to incommode the navigation through the arch, from the fall and quick motion of the water; but likewise to put the bridge itself in much danger, especially in time of floods, when the water is too much for the passage. Add to this, that besides the danger there is of the pier bursting out the sterlings, they are also subject to much decay and damage by the velocity of the water and the craft passing through the arches.

Thrust. See DRIFT.

Voussoirs, the stones which immediately form the arch, their undersides constituting the intrados. The middle one, or key-stone, should be about ¹⁄₁₅th or ¹⁄₁₆th of the span, as has been observed; and the rest should increase in size all the way down to the impost: the more they increase the better, as they will the better bear the great weight which rests upon them without being crushed; and also will bind the firmer together. Their joints should also be cut perpendicular to the curve of the intrados. For more information, see Professor Hutton’s Principles of Bridges, in 8vo.

BRIDGE, in gunnery, the two pieces of timber which go between the two transoms of a gun-carriage, on which the coins are placed, for elevating the piece. See CARRIAGE.

BRIDLE-Arm Protect, a guard used by the cavalry, which consists in having the sword-hilt above the helmet; the blade crossing the back of the head, the point of the left shoulder, and the bridle-arm; its edge directed to the left, and turned a little upwards, in order to bring the mounting in a proper direction to protect the hand.

BRIDON, or BRIDOON, the snaffle and rein of a military bridle, which acts independent of the bit and curb at the pleasure of the rider.

BRIGADE, in military affairs, implies a party or division of a body of soldiers, whether horse, foot, or artillery, under the command of a brigadier. There are, properly speaking, three sorts of brigades, viz. the brigade of an army, the brigade of a troop of horse, and the brigade of artillery. A brigade of the army is either foot or dragoons, whose exact number is not fixed, but generally consists of 3, 4, 5 or 6 regiments, or battalions: a brigade of horse may consist of 8, 10 or 12 squadrons; and that of artillery, of 6, 8 or 10 pieces of cannon, with all their appurtenances. The eldest brigade takes the right of the first line, the second of the second line, and the rest in order, the youngest always possessing the centre, unless the commander deems a different arrangement expedient; and in such case mere etiquette always bends to orders. The cavalry and artillery observe the same order.

The Horse Artillery in the British service are called the horse Brigade; and consist of 6 troops, with their guns and stores. Their head-quarters are at Woolwich, where handsome barracks, detached from those of the royal artillery, have been erected for their accommodation.

A BRIGADE, in the French ordination, is the same as our Regiment; but it consists of 3 battalions, each of which is equal to one of our regiments or 1000 men; a demi brigade is half a regiment, or a French battalion.

BRIGADE-Major, an officer appointed by the brigadier, to assist him in the management of his brigade. The most experienced captains are generally nominated to this post; who act in the brigade as major-generals do in the armies, receiving their orders from their commanders.

BRIGADE-Major-General. The military commands in Great Britain being divided into districts, an office has been established for the sole transaction of brigade duties. Through this office all orders from the commander-in-chief to the generals of districts relative to corps of officers, &c. must pass. For further information on this head, see James’s Regimental Companion, 2d edition, vol. i. page 25.

BRIGADE de Boulangers, Fr. It was usual in the old French service, to brigade the bakers belonging to the army. Each brigade consisted of one master baker and three boys; the system is continued in the modern French army.

BRIGADIER, a military officer, whose rank is next above that of a colonel; appointed to command a corps, consisting of several battalions or regiments, called a brigade. This title in England is suppressed in time of peace, but revived in actual service in the field. Every brigadier marches at the head of his brigade upon duty. On the United States establishment, there is only one brigadier-general, who is chief in actual command; provision has been lately made by law for two more in case of war.

BRIGANDINE, or BRIGANTINE, in ancient military history, a coat of mail, or kind of defensive armor, consisting of tin.

BRINGERS-up, an antiquated military expression, to signify the whole rear rank of a battalion drawn up, as being the hindmost men of every file.