272
HISTORY OF ENGINEERING.
Rook I.
64 feet thick, which rises to the under side of the pavement. The height of the piersis 19 feet 3 inches, and their foundations are laid in steps which project altogether 6feet 5 inches. The platform is laid 8 feet 6 inches below low water, which gives a totalheight of 27 feet 9 inches to the springings, the thickness of the arches is 4 feet 9 inches atthe summit. The breadth of the bridge is 41 feet 6 inches; the arches were turned ontrussed centres, according to Perronet’s system.
The piers are not as usual a solid mass; they, as well as the half piers attached to theabutments, are composed of two groups of columns, leaving a space of 9 feet 7 inchesbetween them. The base of the interval is formed by a reversed arch, and the top iscovered by a lunette, which penetrates the vaults of two adjacent arches. The courses ofeach column are formed by pentagonal newels, which occupies the centre, and five stonescut like wedges applied to each side of the newels ; an iron rod passing through the axisof the column traverses the newels from top to bottom ; the wedges are united to oneanother, and to the newels, by cramps ; the courses are bolted together, the five first coursesof voussoirs, the fourteenth, fifteenth, and twenty-sixth rows are entirely cramped; in theother courses, except the twenty-eighth and the keys, the faces only are cramped. Duringthe construction, advantage was taken of the force of the current to drive the piles, so thatthere were only three men to each engine, and the stones were raised by cranes.
The arch adjoining the left bank was blown up in 1814, but was not entirely destroyed.On the upper side of the bridge a zone 8 feet 6 inches wide remained, in which the voussoirs,especially at the summit, were fractured and displaced. The middle arch had suffered aslight settlement of 3 inches on the upper, and 6^ inches on the lower side, in consequenceof which the joints opened at the intrados of the summit, and the extrados of thespringings. The group of columns to the first pier have gone over J inch up the stream,and 1^ inch down it. The arch on the right bank was not injured.
After having strutted the pier, the arch was restored by constructing in succession a firstzone to the front arch, a second in the middle, and a third to the other front, replacing thatwhich remained after the explosion. Some of the voussoirs were left out to be placed afterit had settled; the whole was finished in 1816, and the details, which arc extremely in-teresting, are given in the “Etudes pour l’Art de Construction,” by M. Bruyere.
Bridge of BumiUy , on the Chcran, built in 1785 by M. Garella, consists of a semicirculararch 128 feet in diameter ; the springing is 10 feet 8 inches below low water. The widthis only 23 feet 5 inches. This is the largest semicircular arch constructed in France duringthe last century.
Bridge of Vizile, on the Romanche , constructed by INI. Roucliet, on the road fromGrenoble to Brian^on. It consists of a single elliptical arch 137 feet 5 inches in span, and38 feet 4 inches high. The thickness of the keystone is 6 feet 4 inches, and that of theabutments 32 feet.
Bridge of Lempde, on the Alagnon, built 1785, by INI. Mauricet, is an elliptical arch101 feet in span.
Bridge of Ilomps, on the Aude, constructed 1785 by M. Ducros, consisting of three seg-mental arches, one-sixth of a circle, with a span of 70 feet 2 inches; the arch on the facesis flatter than that of the centre of the vault, and small comes dc vachcs are constructed,winch terminate on the crowns of the starling.
Bridge of Chateau-Thierry , on the-Marne, begun 1765, finished 1786, after a design by!\L Perronct: it consists of three elliptical arches rising a third, 51 feet 2 inches and 47 feet
3 inches in span; the breadth is 35 feet 2 inches; the thickness of the piers is 14 feet
4 inches, and that of the abutments, which are strengthened by return walls, is 15 feet.The foundation is laid on a frame of carpentry, supported on piles 13 feet 7 inches belowthe springing of the arches ; the thickness of the keystone is 4 feet in the centre arch, and3 feet 9 inches in the two others.
Bridge of Mazeres, on the Lers, built in 1787, by M. Pcrtinchamp ; it is composed of anancient segmental arch, 70 feet 2 inches in span, and two modern semicircular arches,44 feet 7 inches and 48 feet 6 inches in span. They are decorated with an archivolt, andthe pier, which has no starlings, is faced by pilasters. The decorations have a tolerablygood effect, but the omission of starlings is in most cases attended with inconveniences.
Bridge of Chavannes , at Chalons -on-the-Saune, constructed in 1787, at the extremity ofone of the faubourgs, by M. Gauthey. It consists of seven elliptical arches, rising a third,42 feet 8 inches in span ; the height of the piers is 8 feet 6 inches, and the thickness 15 feet,the width is 32 feet.
The situation not permitting the pavement to be sufficiently elevated, high floods rise tothe key of the arches, and in order to compensate for the diminution of water-way the riverundergoes in rising, oval openings 8 feet 6 inches wide are made in the upper part of thepiers. The foundation is a coarse gravel, so compact that the piles could not be drivenmore than 4 feet 3 inches into it. Constructions raised on such soils being very liable tosettlements, a timber platform was placed under the bridge, 52 feet 6 inches wide, and3 feet 3 inches thick, the upper surface being 3 feet 3 inches below low water.