Chap. VI.

FRANCE.

257

Bridge of Trilport , on the Maine , projected and executed by M. Chezy, who began it in1756 and finished it in 1760; the outlay was 489,000 livres ; it consists of three ellipticalarches ; the centre is 81 feet span, the two others76 feet 9 inches. The thickness of the piers is7 feet 5 inches, that of the abutments 19 feet

2 inches. The breadth of the bridge is 32 feet. f HMl j Lj r;'j

The arches are skewed, their axes making an 1

angle of 72 degrees with that of the bridge; thefoundations are on piles and a timber framework, ^

and the water was pumped out by means of avertical chain pump and a bucket-wheel drivenby the current.

To avoid the acute angles which the joints ofthe voussoirs would have formed with the bridge,from the skewing of the arches, Chezy introducedhalf-voussoirs or comes de vache on each sideof the bridge, the breadth of which is 5 feet

3 inches at the springing, gradually diminishingto nothing at the summit of the arch ; the half-voussoir is comprised between the plane of thehead and another vertical plane. The surface ofthe intrados is described by a horizontal gene-rator, perpendicular to the plane of the head,passing through the intersection of the verticalplane just mentioned, with the vault of the arch.

The planes of the joint of the voussoir passthrough the intersections of the planes of thejoint of the vault with this same vertical plane,and through the generators of the voussoirs.

The details and working drawings of thesearches are given in a treatise by M. Bruyere, en-titled, “ Etudes relative al’Art de Construction.”

The bridge of Trilport was destroyed in 1815,the middle arch was removed, and the two piersyielded to the pressure of the lateral arches.

Bridge of Port de Piles , on the Creuse , erectedin 1747 by Bayeux: it consists of three ellip-tical arches rising one-third, and from 99 feet to103 feet 8 inches span. The voussoirs were laidon beds of mortar beaten with a mallet, and in theirjoints, to the sixth course from the key-stone, longand wide wooden wedges were introduced, bymeans of which the compression was so regulated (that when the centres were removed, the great Jarch sank only an inch, and the two others rather Vless. \\

Bridge of the Pope, on the Erieux, constructed >in 1756 by Pitot, consisting of seven arches ,nearly semicircular, 48 feet 6 inches span. It is 'of squared stone; the abutments are founded ona rock, but all the piers are built on piles. Ageneral framewurk was constructed by drivingtwo rows of piles capped both up and down thestream.

Bridge of Orleans, on the Loire, begun in 1751 / y\ IL I !

from designs by M. Hupeau. The work was / f\ wSfa ^wI 1

carried on under his orders by Soyer, and was \r jH i-li

finished in 1760. Pitrou had made a nearlysimilar design, except that the situation was alittle different, and the radius of the arches atthe springing was greater, which tended toincrease the water-way. \

It consists of nine elliptical arches rising a \fourth, from 98 feet 1 inch to 106 feet 7 inches 1in span. The piers are from 6 feet 3 inches to -

10 feet 7 inches high, and from 18 feet 2 inches ^

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Fig. 2f>2. BRIDGE OF TRILPORT ON THE MAINE.