1363

THEORY AND PRACTICE OF ENGINEERING.

Book II.

a colonello or post, in which the centre braces meet, and on the upper part of which mustbe fixed other braces, uniting with the next colonello, tying all together, and forming withthe braces m the head of the bridge a portion of a circle less than a semicircle.

Foot Bridge , over the canal of Gooda, in Holland, 45 feet span, is of very simpleconstruction ; it is formed of curved timber, framed to resemble the segment of anarch. There are two sets of ribs, on which rest the longitudinal bearers that carry aplanked floor, 4 feet 6 inches clear width between the parapets or railing: the posts intowhich the horizontal rails are mortised, by an additional length unite and hold together thecurved and straight timbers, on which the platform rests.

GOODA IN HOLLAND.

Another Foot Bridge in Holland , over the canal at Utrecht , of the same span, showsgreater strength; its clear width between the railing is 5 feet 6 inches; struts are in-troduced, held in their positions by couples or pendant binding-pieces.

UTRECHT CANAL.

Fig. ‘2227.

Mulatiere Bridge at Lyons, over the Saone , has eleven openings; the centre is 57 feet6 inches, and the others gradually diminish to 49 feet span. The piers are each formedof two rows of piles, driven parallel to each other : three horizontal pieces of timberbolt them together above the water : on the tops are framed abutments like those ofTrajan’s bridge, receiving the thrust of the principal timbers: each opening has an

Fig. 2228. MULATIERE AT LYONS.

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arch, formed of four sides of a polygon; each of these sides consists of two pieces oftimber, framed or scarfed together, one being cut like the teeth of a saw, and the otherindented to receive it: after these are fitted they are securely bolted together. Wherethe ends of these pairs of timbers unite and abut against each other are pendantbinding-pieces, to hold up and secure them to the principal longitudinal timbers whichcarry the platform: the error of this kind of construction arises in part from thependant pieces maintaining a constant humidity, which is communicated in time to thepolygonal pairs of timbers and the framed abutments, when a partial decay takes place,and a settlement follows.

The timber bridges at Kingston-upon-Thames , Walton, and many others in England,ware constructed upon this principle, and were constantly requiring repairs.